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900 lines
30 KiB
Python
900 lines
30 KiB
Python
"""
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Binary serialization
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NPY format
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==========
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A simple format for saving numpy arrays to disk with the full
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information about them.
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The ``.npy`` format is the standard binary file format in NumPy for
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persisting a *single* arbitrary NumPy array on disk. The format stores all
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of the shape and dtype information necessary to reconstruct the array
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correctly even on another machine with a different architecture.
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The format is designed to be as simple as possible while achieving
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its limited goals.
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The ``.npz`` format is the standard format for persisting *multiple* NumPy
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arrays on disk. A ``.npz`` file is a zip file containing multiple ``.npy``
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files, one for each array.
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Capabilities
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------------
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- Can represent all NumPy arrays including nested record arrays and
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object arrays.
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- Represents the data in its native binary form.
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- Supports Fortran-contiguous arrays directly.
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- Stores all of the necessary information to reconstruct the array
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including shape and dtype on a machine of a different
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architecture. Both little-endian and big-endian arrays are
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supported, and a file with little-endian numbers will yield
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a little-endian array on any machine reading the file. The
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types are described in terms of their actual sizes. For example,
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if a machine with a 64-bit C "long int" writes out an array with
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"long ints", a reading machine with 32-bit C "long ints" will yield
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an array with 64-bit integers.
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- Is straightforward to reverse engineer. Datasets often live longer than
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the programs that created them. A competent developer should be
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able to create a solution in their preferred programming language to
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read most ``.npy`` files that he has been given without much
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documentation.
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- Allows memory-mapping of the data. See `open_memmep`.
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- Can be read from a filelike stream object instead of an actual file.
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- Stores object arrays, i.e. arrays containing elements that are arbitrary
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Python objects. Files with object arrays are not to be mmapable, but
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can be read and written to disk.
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Limitations
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-----------
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- Arbitrary subclasses of numpy.ndarray are not completely preserved.
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Subclasses will be accepted for writing, but only the array data will
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be written out. A regular numpy.ndarray object will be created
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upon reading the file.
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.. warning::
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Due to limitations in the interpretation of structured dtypes, dtypes
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with fields with empty names will have the names replaced by 'f0', 'f1',
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etc. Such arrays will not round-trip through the format entirely
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accurately. The data is intact; only the field names will differ. We are
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working on a fix for this. This fix will not require a change in the
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file format. The arrays with such structures can still be saved and
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restored, and the correct dtype may be restored by using the
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``loadedarray.view(correct_dtype)`` method.
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File extensions
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---------------
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We recommend using the ``.npy`` and ``.npz`` extensions for files saved
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in this format. This is by no means a requirement; applications may wish
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to use these file formats but use an extension specific to the
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application. In the absence of an obvious alternative, however,
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we suggest using ``.npy`` and ``.npz``.
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Version numbering
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-----------------
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The version numbering of these formats is independent of NumPy version
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numbering. If the format is upgraded, the code in `numpy.io` will still
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be able to read and write Version 1.0 files.
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Format Version 1.0
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------------------
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The first 6 bytes are a magic string: exactly ``\\x93NUMPY``.
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The next 1 byte is an unsigned byte: the major version number of the file
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format, e.g. ``\\x01``.
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The next 1 byte is an unsigned byte: the minor version number of the file
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format, e.g. ``\\x00``. Note: the version of the file format is not tied
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to the version of the numpy package.
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The next 2 bytes form a little-endian unsigned short int: the length of
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the header data HEADER_LEN.
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The next HEADER_LEN bytes form the header data describing the array's
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format. It is an ASCII string which contains a Python literal expression
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of a dictionary. It is terminated by a newline (``\\n``) and padded with
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spaces (``\\x20``) to make the total of
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``len(magic string) + 2 + len(length) + HEADER_LEN`` be evenly divisible
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by 64 for alignment purposes.
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The dictionary contains three keys:
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"descr" : dtype.descr
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An object that can be passed as an argument to the `numpy.dtype`
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constructor to create the array's dtype.
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"fortran_order" : bool
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Whether the array data is Fortran-contiguous or not. Since
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Fortran-contiguous arrays are a common form of non-C-contiguity,
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we allow them to be written directly to disk for efficiency.
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"shape" : tuple of int
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The shape of the array.
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For repeatability and readability, the dictionary keys are sorted in
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alphabetic order. This is for convenience only. A writer SHOULD implement
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this if possible. A reader MUST NOT depend on this.
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Following the header comes the array data. If the dtype contains Python
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objects (i.e. ``dtype.hasobject is True``), then the data is a Python
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pickle of the array. Otherwise the data is the contiguous (either C-
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or Fortran-, depending on ``fortran_order``) bytes of the array.
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Consumers can figure out the number of bytes by multiplying the number
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of elements given by the shape (noting that ``shape=()`` means there is
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1 element) by ``dtype.itemsize``.
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Format Version 2.0
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------------------
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The version 1.0 format only allowed the array header to have a total size of
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65535 bytes. This can be exceeded by structured arrays with a large number of
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columns. The version 2.0 format extends the header size to 4 GiB.
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`numpy.save` will automatically save in 2.0 format if the data requires it,
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else it will always use the more compatible 1.0 format.
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The description of the fourth element of the header therefore has become:
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"The next 4 bytes form a little-endian unsigned int: the length of the header
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data HEADER_LEN."
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Format Version 3.0
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------------------
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This version replaces the ASCII string (which in practice was latin1) with
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a utf8-encoded string, so supports structured types with any unicode field
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names.
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Notes
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-----
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The ``.npy`` format, including motivation for creating it and a comparison of
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alternatives, is described in the `"npy-format" NEP
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<https://www.numpy.org/neps/nep-0001-npy-format.html>`_, however details have
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evolved with time and this document is more current.
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"""
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from __future__ import division, absolute_import, print_function
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import numpy
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import sys
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import io
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import warnings
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from numpy.lib.utils import safe_eval
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from numpy.compat import (
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isfileobj, long, os_fspath, pickle
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)
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MAGIC_PREFIX = b'\x93NUMPY'
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MAGIC_LEN = len(MAGIC_PREFIX) + 2
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ARRAY_ALIGN = 64 # plausible values are powers of 2 between 16 and 4096
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BUFFER_SIZE = 2**18 # size of buffer for reading npz files in bytes
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# difference between version 1.0 and 2.0 is a 4 byte (I) header length
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# instead of 2 bytes (H) allowing storage of large structured arrays
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_header_size_info = {
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(1, 0): ('<H', 'latin1'),
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(2, 0): ('<I', 'latin1'),
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(3, 0): ('<I', 'utf8'),
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}
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def _check_version(version):
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if version not in [(1, 0), (2, 0), (3, 0), None]:
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msg = "we only support format version (1,0), (2,0), and (3,0), not %s"
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raise ValueError(msg % (version,))
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def magic(major, minor):
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""" Return the magic string for the given file format version.
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Parameters
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----------
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major : int in [0, 255]
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minor : int in [0, 255]
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Returns
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-------
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magic : str
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Raises
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------
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ValueError if the version cannot be formatted.
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"""
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if major < 0 or major > 255:
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raise ValueError("major version must be 0 <= major < 256")
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if minor < 0 or minor > 255:
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raise ValueError("minor version must be 0 <= minor < 256")
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if sys.version_info[0] < 3:
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return MAGIC_PREFIX + chr(major) + chr(minor)
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else:
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return MAGIC_PREFIX + bytes([major, minor])
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def read_magic(fp):
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""" Read the magic string to get the version of the file format.
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Parameters
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----------
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fp : filelike object
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Returns
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-------
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major : int
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minor : int
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"""
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magic_str = _read_bytes(fp, MAGIC_LEN, "magic string")
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if magic_str[:-2] != MAGIC_PREFIX:
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msg = "the magic string is not correct; expected %r, got %r"
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raise ValueError(msg % (MAGIC_PREFIX, magic_str[:-2]))
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if sys.version_info[0] < 3:
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major, minor = map(ord, magic_str[-2:])
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else:
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major, minor = magic_str[-2:]
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return major, minor
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def dtype_to_descr(dtype):
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"""
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Get a serializable descriptor from the dtype.
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The .descr attribute of a dtype object cannot be round-tripped through
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the dtype() constructor. Simple types, like dtype('float32'), have
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a descr which looks like a record array with one field with '' as
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a name. The dtype() constructor interprets this as a request to give
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a default name. Instead, we construct descriptor that can be passed to
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dtype().
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Parameters
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----------
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dtype : dtype
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The dtype of the array that will be written to disk.
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Returns
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-------
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descr : object
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An object that can be passed to `numpy.dtype()` in order to
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replicate the input dtype.
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"""
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if dtype.names is not None:
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# This is a record array. The .descr is fine. XXX: parts of the
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# record array with an empty name, like padding bytes, still get
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# fiddled with. This needs to be fixed in the C implementation of
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# dtype().
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return dtype.descr
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else:
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return dtype.str
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def descr_to_dtype(descr):
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'''
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descr may be stored as dtype.descr, which is a list of
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(name, format, [shape]) tuples where format may be a str or a tuple.
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Offsets are not explicitly saved, rather empty fields with
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name, format == '', '|Vn' are added as padding.
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This function reverses the process, eliminating the empty padding fields.
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'''
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if isinstance(descr, str):
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# No padding removal needed
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return numpy.dtype(descr)
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elif isinstance(descr, tuple):
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# subtype, will always have a shape descr[1]
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dt = descr_to_dtype(descr[0])
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return numpy.dtype((dt, descr[1]))
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fields = []
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offset = 0
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for field in descr:
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if len(field) == 2:
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name, descr_str = field
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dt = descr_to_dtype(descr_str)
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else:
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name, descr_str, shape = field
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dt = numpy.dtype((descr_to_dtype(descr_str), shape))
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# Ignore padding bytes, which will be void bytes with '' as name
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# Once support for blank names is removed, only "if name == ''" needed)
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is_pad = (name == '' and dt.type is numpy.void and dt.names is None)
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if not is_pad:
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fields.append((name, dt, offset))
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offset += dt.itemsize
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names, formats, offsets = zip(*fields)
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# names may be (title, names) tuples
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nametups = (n if isinstance(n, tuple) else (None, n) for n in names)
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titles, names = zip(*nametups)
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return numpy.dtype({'names': names, 'formats': formats, 'titles': titles,
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'offsets': offsets, 'itemsize': offset})
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def header_data_from_array_1_0(array):
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""" Get the dictionary of header metadata from a numpy.ndarray.
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Parameters
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----------
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array : numpy.ndarray
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Returns
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-------
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d : dict
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This has the appropriate entries for writing its string representation
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to the header of the file.
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"""
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d = {'shape': array.shape}
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if array.flags.c_contiguous:
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d['fortran_order'] = False
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elif array.flags.f_contiguous:
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d['fortran_order'] = True
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else:
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# Totally non-contiguous data. We will have to make it C-contiguous
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# before writing. Note that we need to test for C_CONTIGUOUS first
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# because a 1-D array is both C_CONTIGUOUS and F_CONTIGUOUS.
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d['fortran_order'] = False
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d['descr'] = dtype_to_descr(array.dtype)
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return d
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def _wrap_header(header, version):
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"""
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Takes a stringified header, and attaches the prefix and padding to it
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"""
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import struct
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assert version is not None
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fmt, encoding = _header_size_info[version]
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if not isinstance(header, bytes): # always true on python 3
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header = header.encode(encoding)
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hlen = len(header) + 1
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padlen = ARRAY_ALIGN - ((MAGIC_LEN + struct.calcsize(fmt) + hlen) % ARRAY_ALIGN)
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try:
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header_prefix = magic(*version) + struct.pack(fmt, hlen + padlen)
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except struct.error:
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msg = "Header length {} too big for version={}".format(hlen, version)
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raise ValueError(msg)
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# Pad the header with spaces and a final newline such that the magic
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# string, the header-length short and the header are aligned on a
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# ARRAY_ALIGN byte boundary. This supports memory mapping of dtypes
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# aligned up to ARRAY_ALIGN on systems like Linux where mmap()
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# offset must be page-aligned (i.e. the beginning of the file).
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return header_prefix + header + b' '*padlen + b'\n'
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def _wrap_header_guess_version(header):
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"""
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Like `_wrap_header`, but chooses an appropriate version given the contents
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"""
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try:
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return _wrap_header(header, (1, 0))
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except ValueError:
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pass
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try:
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ret = _wrap_header(header, (2, 0))
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except UnicodeEncodeError:
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pass
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else:
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warnings.warn("Stored array in format 2.0. It can only be"
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"read by NumPy >= 1.9", UserWarning, stacklevel=2)
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return ret
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header = _wrap_header(header, (3, 0))
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warnings.warn("Stored array in format 3.0. It can only be"
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"read by NumPy >= 1.17", UserWarning, stacklevel=2)
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return header
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def _write_array_header(fp, d, version=None):
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""" Write the header for an array and returns the version used
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Parameters
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----------
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fp : filelike object
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d : dict
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This has the appropriate entries for writing its string representation
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to the header of the file.
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version: tuple or None
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None means use oldest that works
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explicit version will raise a ValueError if the format does not
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allow saving this data. Default: None
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"""
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header = ["{"]
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for key, value in sorted(d.items()):
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# Need to use repr here, since we eval these when reading
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header.append("'%s': %s, " % (key, repr(value)))
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header.append("}")
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header = "".join(header)
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header = _filter_header(header)
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if version is None:
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header = _wrap_header_guess_version(header)
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else:
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header = _wrap_header(header, version)
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fp.write(header)
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def write_array_header_1_0(fp, d):
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""" Write the header for an array using the 1.0 format.
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|
Parameters
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----------
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fp : filelike object
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d : dict
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This has the appropriate entries for writing its string
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representation to the header of the file.
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"""
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_write_array_header(fp, d, (1, 0))
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|
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def write_array_header_2_0(fp, d):
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""" Write the header for an array using the 2.0 format.
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The 2.0 format allows storing very large structured arrays.
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.. versionadded:: 1.9.0
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|
Parameters
|
|
----------
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fp : filelike object
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d : dict
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This has the appropriate entries for writing its string
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representation to the header of the file.
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"""
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_write_array_header(fp, d, (2, 0))
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def read_array_header_1_0(fp):
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"""
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Read an array header from a filelike object using the 1.0 file format
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version.
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This will leave the file object located just after the header.
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|
Parameters
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----------
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fp : filelike object
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A file object or something with a `.read()` method like a file.
|
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|
|
Returns
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-------
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shape : tuple of int
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The shape of the array.
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fortran_order : bool
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The array data will be written out directly if it is either
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C-contiguous or Fortran-contiguous. Otherwise, it will be made
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|
contiguous before writing it out.
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dtype : dtype
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The dtype of the file's data.
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|
Raises
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|
------
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|
ValueError
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If the data is invalid.
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"""
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return _read_array_header(fp, version=(1, 0))
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|
|
def read_array_header_2_0(fp):
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"""
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|
Read an array header from a filelike object using the 2.0 file format
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|
version.
|
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This will leave the file object located just after the header.
|
|
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|
.. versionadded:: 1.9.0
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|
Parameters
|
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----------
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fp : filelike object
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A file object or something with a `.read()` method like a file.
|
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|
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Returns
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-------
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shape : tuple of int
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The shape of the array.
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fortran_order : bool
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The array data will be written out directly if it is either
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C-contiguous or Fortran-contiguous. Otherwise, it will be made
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|
contiguous before writing it out.
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dtype : dtype
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|
The dtype of the file's data.
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|
|
Raises
|
|
------
|
|
ValueError
|
|
If the data is invalid.
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"""
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return _read_array_header(fp, version=(2, 0))
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|
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def _filter_header(s):
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"""Clean up 'L' in npz header ints.
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|
Cleans up the 'L' in strings representing integers. Needed to allow npz
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headers produced in Python2 to be read in Python3.
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Parameters
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----------
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s : string
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Npy file header.
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Returns
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-------
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header : str
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Cleaned up header.
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"""
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|
import tokenize
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|
if sys.version_info[0] >= 3:
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|
from io import StringIO
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|
else:
|
|
from StringIO import StringIO
|
|
|
|
tokens = []
|
|
last_token_was_number = False
|
|
# adding newline as python 2.7.5 workaround
|
|
string = s + "\n"
|
|
for token in tokenize.generate_tokens(StringIO(string).readline):
|
|
token_type = token[0]
|
|
token_string = token[1]
|
|
if (last_token_was_number and
|
|
token_type == tokenize.NAME and
|
|
token_string == "L"):
|
|
continue
|
|
else:
|
|
tokens.append(token)
|
|
last_token_was_number = (token_type == tokenize.NUMBER)
|
|
# removing newline (see above) as python 2.7.5 workaround
|
|
return tokenize.untokenize(tokens)[:-1]
|
|
|
|
|
|
def _read_array_header(fp, version):
|
|
"""
|
|
see read_array_header_1_0
|
|
"""
|
|
# Read an unsigned, little-endian short int which has the length of the
|
|
# header.
|
|
import struct
|
|
hinfo = _header_size_info.get(version)
|
|
if hinfo is None:
|
|
raise ValueError("Invalid version {!r}".format(version))
|
|
hlength_type, encoding = hinfo
|
|
|
|
hlength_str = _read_bytes(fp, struct.calcsize(hlength_type), "array header length")
|
|
header_length = struct.unpack(hlength_type, hlength_str)[0]
|
|
header = _read_bytes(fp, header_length, "array header")
|
|
header = header.decode(encoding)
|
|
|
|
# The header is a pretty-printed string representation of a literal
|
|
# Python dictionary with trailing newlines padded to a ARRAY_ALIGN byte
|
|
# boundary. The keys are strings.
|
|
# "shape" : tuple of int
|
|
# "fortran_order" : bool
|
|
# "descr" : dtype.descr
|
|
header = _filter_header(header)
|
|
try:
|
|
d = safe_eval(header)
|
|
except SyntaxError as e:
|
|
msg = "Cannot parse header: {!r}\nException: {!r}"
|
|
raise ValueError(msg.format(header, e))
|
|
if not isinstance(d, dict):
|
|
msg = "Header is not a dictionary: {!r}"
|
|
raise ValueError(msg.format(d))
|
|
keys = sorted(d.keys())
|
|
if keys != ['descr', 'fortran_order', 'shape']:
|
|
msg = "Header does not contain the correct keys: {!r}"
|
|
raise ValueError(msg.format(keys))
|
|
|
|
# Sanity-check the values.
|
|
if (not isinstance(d['shape'], tuple) or
|
|
not numpy.all([isinstance(x, (int, long)) for x in d['shape']])):
|
|
msg = "shape is not valid: {!r}"
|
|
raise ValueError(msg.format(d['shape']))
|
|
if not isinstance(d['fortran_order'], bool):
|
|
msg = "fortran_order is not a valid bool: {!r}"
|
|
raise ValueError(msg.format(d['fortran_order']))
|
|
try:
|
|
dtype = descr_to_dtype(d['descr'])
|
|
except TypeError as e:
|
|
msg = "descr is not a valid dtype descriptor: {!r}"
|
|
raise ValueError(msg.format(d['descr']))
|
|
|
|
return d['shape'], d['fortran_order'], dtype
|
|
|
|
def write_array(fp, array, version=None, allow_pickle=True, pickle_kwargs=None):
|
|
"""
|
|
Write an array to an NPY file, including a header.
|
|
|
|
If the array is neither C-contiguous nor Fortran-contiguous AND the
|
|
file_like object is not a real file object, this function will have to
|
|
copy data in memory.
|
|
|
|
Parameters
|
|
----------
|
|
fp : file_like object
|
|
An open, writable file object, or similar object with a
|
|
``.write()`` method.
|
|
array : ndarray
|
|
The array to write to disk.
|
|
version : (int, int) or None, optional
|
|
The version number of the format. None means use the oldest
|
|
supported version that is able to store the data. Default: None
|
|
allow_pickle : bool, optional
|
|
Whether to allow writing pickled data. Default: True
|
|
pickle_kwargs : dict, optional
|
|
Additional keyword arguments to pass to pickle.dump, excluding
|
|
'protocol'. These are only useful when pickling objects in object
|
|
arrays on Python 3 to Python 2 compatible format.
|
|
|
|
Raises
|
|
------
|
|
ValueError
|
|
If the array cannot be persisted. This includes the case of
|
|
allow_pickle=False and array being an object array.
|
|
Various other errors
|
|
If the array contains Python objects as part of its dtype, the
|
|
process of pickling them may raise various errors if the objects
|
|
are not picklable.
|
|
|
|
"""
|
|
_check_version(version)
|
|
_write_array_header(fp, header_data_from_array_1_0(array), version)
|
|
|
|
if array.itemsize == 0:
|
|
buffersize = 0
|
|
else:
|
|
# Set buffer size to 16 MiB to hide the Python loop overhead.
|
|
buffersize = max(16 * 1024 ** 2 // array.itemsize, 1)
|
|
|
|
if array.dtype.hasobject:
|
|
# We contain Python objects so we cannot write out the data
|
|
# directly. Instead, we will pickle it out
|
|
if not allow_pickle:
|
|
raise ValueError("Object arrays cannot be saved when "
|
|
"allow_pickle=False")
|
|
if pickle_kwargs is None:
|
|
pickle_kwargs = {}
|
|
pickle.dump(array, fp, protocol=3, **pickle_kwargs)
|
|
elif array.flags.f_contiguous and not array.flags.c_contiguous:
|
|
if isfileobj(fp):
|
|
array.T.tofile(fp)
|
|
else:
|
|
for chunk in numpy.nditer(
|
|
array, flags=['external_loop', 'buffered', 'zerosize_ok'],
|
|
buffersize=buffersize, order='F'):
|
|
fp.write(chunk.tobytes('C'))
|
|
else:
|
|
if isfileobj(fp):
|
|
array.tofile(fp)
|
|
else:
|
|
for chunk in numpy.nditer(
|
|
array, flags=['external_loop', 'buffered', 'zerosize_ok'],
|
|
buffersize=buffersize, order='C'):
|
|
fp.write(chunk.tobytes('C'))
|
|
|
|
|
|
def read_array(fp, allow_pickle=False, pickle_kwargs=None):
|
|
"""
|
|
Read an array from an NPY file.
|
|
|
|
Parameters
|
|
----------
|
|
fp : file_like object
|
|
If this is not a real file object, then this may take extra memory
|
|
and time.
|
|
allow_pickle : bool, optional
|
|
Whether to allow writing pickled data. Default: False
|
|
|
|
.. versionchanged:: 1.16.3
|
|
Made default False in response to CVE-2019-6446.
|
|
|
|
pickle_kwargs : dict
|
|
Additional keyword arguments to pass to pickle.load. These are only
|
|
useful when loading object arrays saved on Python 2 when using
|
|
Python 3.
|
|
|
|
Returns
|
|
-------
|
|
array : ndarray
|
|
The array from the data on disk.
|
|
|
|
Raises
|
|
------
|
|
ValueError
|
|
If the data is invalid, or allow_pickle=False and the file contains
|
|
an object array.
|
|
|
|
"""
|
|
version = read_magic(fp)
|
|
_check_version(version)
|
|
shape, fortran_order, dtype = _read_array_header(fp, version)
|
|
if len(shape) == 0:
|
|
count = 1
|
|
else:
|
|
count = numpy.multiply.reduce(shape, dtype=numpy.int64)
|
|
|
|
# Now read the actual data.
|
|
if dtype.hasobject:
|
|
# The array contained Python objects. We need to unpickle the data.
|
|
if not allow_pickle:
|
|
raise ValueError("Object arrays cannot be loaded when "
|
|
"allow_pickle=False")
|
|
if pickle_kwargs is None:
|
|
pickle_kwargs = {}
|
|
try:
|
|
array = pickle.load(fp, **pickle_kwargs)
|
|
except UnicodeError as err:
|
|
if sys.version_info[0] >= 3:
|
|
# Friendlier error message
|
|
raise UnicodeError("Unpickling a python object failed: %r\n"
|
|
"You may need to pass the encoding= option "
|
|
"to numpy.load" % (err,))
|
|
raise
|
|
else:
|
|
if isfileobj(fp):
|
|
# We can use the fast fromfile() function.
|
|
array = numpy.fromfile(fp, dtype=dtype, count=count)
|
|
else:
|
|
# This is not a real file. We have to read it the
|
|
# memory-intensive way.
|
|
# crc32 module fails on reads greater than 2 ** 32 bytes,
|
|
# breaking large reads from gzip streams. Chunk reads to
|
|
# BUFFER_SIZE bytes to avoid issue and reduce memory overhead
|
|
# of the read. In non-chunked case count < max_read_count, so
|
|
# only one read is performed.
|
|
|
|
# Use np.ndarray instead of np.empty since the latter does
|
|
# not correctly instantiate zero-width string dtypes; see
|
|
# https://github.com/numpy/numpy/pull/6430
|
|
array = numpy.ndarray(count, dtype=dtype)
|
|
|
|
if dtype.itemsize > 0:
|
|
# If dtype.itemsize == 0 then there's nothing more to read
|
|
max_read_count = BUFFER_SIZE // min(BUFFER_SIZE, dtype.itemsize)
|
|
|
|
for i in range(0, count, max_read_count):
|
|
read_count = min(max_read_count, count - i)
|
|
read_size = int(read_count * dtype.itemsize)
|
|
data = _read_bytes(fp, read_size, "array data")
|
|
array[i:i+read_count] = numpy.frombuffer(data, dtype=dtype,
|
|
count=read_count)
|
|
|
|
if fortran_order:
|
|
array.shape = shape[::-1]
|
|
array = array.transpose()
|
|
else:
|
|
array.shape = shape
|
|
|
|
return array
|
|
|
|
|
|
def open_memmap(filename, mode='r+', dtype=None, shape=None,
|
|
fortran_order=False, version=None):
|
|
"""
|
|
Open a .npy file as a memory-mapped array.
|
|
|
|
This may be used to read an existing file or create a new one.
|
|
|
|
Parameters
|
|
----------
|
|
filename : str or path-like
|
|
The name of the file on disk. This may *not* be a file-like
|
|
object.
|
|
mode : str, optional
|
|
The mode in which to open the file; the default is 'r+'. In
|
|
addition to the standard file modes, 'c' is also accepted to mean
|
|
"copy on write." See `memmap` for the available mode strings.
|
|
dtype : data-type, optional
|
|
The data type of the array if we are creating a new file in "write"
|
|
mode, if not, `dtype` is ignored. The default value is None, which
|
|
results in a data-type of `float64`.
|
|
shape : tuple of int
|
|
The shape of the array if we are creating a new file in "write"
|
|
mode, in which case this parameter is required. Otherwise, this
|
|
parameter is ignored and is thus optional.
|
|
fortran_order : bool, optional
|
|
Whether the array should be Fortran-contiguous (True) or
|
|
C-contiguous (False, the default) if we are creating a new file in
|
|
"write" mode.
|
|
version : tuple of int (major, minor) or None
|
|
If the mode is a "write" mode, then this is the version of the file
|
|
format used to create the file. None means use the oldest
|
|
supported version that is able to store the data. Default: None
|
|
|
|
Returns
|
|
-------
|
|
marray : memmap
|
|
The memory-mapped array.
|
|
|
|
Raises
|
|
------
|
|
ValueError
|
|
If the data or the mode is invalid.
|
|
IOError
|
|
If the file is not found or cannot be opened correctly.
|
|
|
|
See Also
|
|
--------
|
|
memmap
|
|
|
|
"""
|
|
if isfileobj(filename):
|
|
raise ValueError("Filename must be a string or a path-like object."
|
|
" Memmap cannot use existing file handles.")
|
|
|
|
if 'w' in mode:
|
|
# We are creating the file, not reading it.
|
|
# Check if we ought to create the file.
|
|
_check_version(version)
|
|
# Ensure that the given dtype is an authentic dtype object rather
|
|
# than just something that can be interpreted as a dtype object.
|
|
dtype = numpy.dtype(dtype)
|
|
if dtype.hasobject:
|
|
msg = "Array can't be memory-mapped: Python objects in dtype."
|
|
raise ValueError(msg)
|
|
d = dict(
|
|
descr=dtype_to_descr(dtype),
|
|
fortran_order=fortran_order,
|
|
shape=shape,
|
|
)
|
|
# If we got here, then it should be safe to create the file.
|
|
with open(os_fspath(filename), mode+'b') as fp:
|
|
_write_array_header(fp, d, version)
|
|
offset = fp.tell()
|
|
else:
|
|
# Read the header of the file first.
|
|
with open(os_fspath(filename), 'rb') as fp:
|
|
version = read_magic(fp)
|
|
_check_version(version)
|
|
|
|
shape, fortran_order, dtype = _read_array_header(fp, version)
|
|
if dtype.hasobject:
|
|
msg = "Array can't be memory-mapped: Python objects in dtype."
|
|
raise ValueError(msg)
|
|
offset = fp.tell()
|
|
|
|
if fortran_order:
|
|
order = 'F'
|
|
else:
|
|
order = 'C'
|
|
|
|
# We need to change a write-only mode to a read-write mode since we've
|
|
# already written data to the file.
|
|
if mode == 'w+':
|
|
mode = 'r+'
|
|
|
|
marray = numpy.memmap(filename, dtype=dtype, shape=shape, order=order,
|
|
mode=mode, offset=offset)
|
|
|
|
return marray
|
|
|
|
|
|
def _read_bytes(fp, size, error_template="ran out of data"):
|
|
"""
|
|
Read from file-like object until size bytes are read.
|
|
Raises ValueError if not EOF is encountered before size bytes are read.
|
|
Non-blocking objects only supported if they derive from io objects.
|
|
|
|
Required as e.g. ZipExtFile in python 2.6 can return less data than
|
|
requested.
|
|
"""
|
|
data = bytes()
|
|
while True:
|
|
# io files (default in python3) return None or raise on
|
|
# would-block, python2 file will truncate, probably nothing can be
|
|
# done about that. note that regular files can't be non-blocking
|
|
try:
|
|
r = fp.read(size - len(data))
|
|
data += r
|
|
if len(r) == 0 or len(data) == size:
|
|
break
|
|
except io.BlockingIOError:
|
|
pass
|
|
if len(data) != size:
|
|
msg = "EOF: reading %s, expected %d bytes got %d"
|
|
raise ValueError(msg % (error_template, size, len(data)))
|
|
else:
|
|
return data
|