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271 lines
9.0 KiB
Python
271 lines
9.0 KiB
Python
"""Miscellaneous utility functions and classes.
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This module is used internally by Tornado. It is not necessarily expected
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that the functions and classes defined here will be useful to other
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applications, but they are documented here in case they are.
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The one public-facing part of this module is the `Configurable` class
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and its `~Configurable.configure` method, which becomes a part of the
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interface of its subclasses, including `.AsyncHTTPClient`, `.IOLoop`,
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and `.Resolver`.
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"""
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from __future__ import absolute_import, division, print_function, with_statement
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import inspect
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import sys
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import zlib
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class ObjectDict(dict):
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"""Makes a dictionary behave like an object, with attribute-style access.
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"""
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def __getattr__(self, name):
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try:
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return self[name]
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except KeyError:
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raise AttributeError(name)
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def __setattr__(self, name, value):
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self[name] = value
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class GzipDecompressor(object):
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"""Streaming gzip decompressor.
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The interface is like that of `zlib.decompressobj` (without the
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optional arguments, but it understands gzip headers and checksums.
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"""
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def __init__(self):
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# Magic parameter makes zlib module understand gzip header
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# http://stackoverflow.com/questions/1838699/how-can-i-decompress-a-gzip-stream-with-zlib
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# This works on cpython and pypy, but not jython.
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self.decompressobj = zlib.decompressobj(16 + zlib.MAX_WBITS)
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def decompress(self, value):
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"""Decompress a chunk, returning newly-available data.
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Some data may be buffered for later processing; `flush` must
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be called when there is no more input data to ensure that
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all data was processed.
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"""
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return self.decompressobj.decompress(value)
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def flush(self):
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"""Return any remaining buffered data not yet returned by decompress.
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Also checks for errors such as truncated input.
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No other methods may be called on this object after `flush`.
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"""
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return self.decompressobj.flush()
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def import_object(name):
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"""Imports an object by name.
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import_object('x') is equivalent to 'import x'.
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import_object('x.y.z') is equivalent to 'from x.y import z'.
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>>> import tornado.escape
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>>> import_object('tornado.escape') is tornado.escape
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True
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>>> import_object('tornado.escape.utf8') is tornado.escape.utf8
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True
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>>> import_object('tornado') is tornado
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True
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>>> import_object('tornado.missing_module')
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Traceback (most recent call last):
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...
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ImportError: No module named missing_module
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"""
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if name.count('.') == 0:
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return __import__(name, None, None)
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parts = name.split('.')
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obj = __import__('.'.join(parts[:-1]), None, None, [parts[-1]], 0)
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try:
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return getattr(obj, parts[-1])
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except AttributeError:
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raise ImportError("No module named %s" % parts[-1])
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# Fake unicode literal support: Python 3.2 doesn't have the u'' marker for
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# literal strings, and alternative solutions like "from __future__ import
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# unicode_literals" have other problems (see PEP 414). u() can be applied
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# to ascii strings that include \u escapes (but they must not contain
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# literal non-ascii characters).
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if type('') is not type(b''):
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def u(s):
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return s
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bytes_type = bytes
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unicode_type = str
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basestring_type = str
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else:
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def u(s):
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return s.decode('unicode_escape')
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bytes_type = str
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unicode_type = unicode
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basestring_type = basestring
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if sys.version_info > (3,):
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exec("""
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def raise_exc_info(exc_info):
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raise exc_info[1].with_traceback(exc_info[2])
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def exec_in(code, glob, loc=None):
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if isinstance(code, str):
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code = compile(code, '<string>', 'exec', dont_inherit=True)
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exec(code, glob, loc)
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""")
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else:
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exec("""
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def raise_exc_info(exc_info):
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raise exc_info[0], exc_info[1], exc_info[2]
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def exec_in(code, glob, loc=None):
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if isinstance(code, basestring):
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# exec(string) inherits the caller's future imports; compile
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# the string first to prevent that.
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code = compile(code, '<string>', 'exec', dont_inherit=True)
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exec code in glob, loc
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""")
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class Configurable(object):
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"""Base class for configurable interfaces.
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A configurable interface is an (abstract) class whose constructor
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acts as a factory function for one of its implementation subclasses.
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The implementation subclass as well as optional keyword arguments to
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its initializer can be set globally at runtime with `configure`.
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By using the constructor as the factory method, the interface
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looks like a normal class, `isinstance` works as usual, etc. This
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pattern is most useful when the choice of implementation is likely
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to be a global decision (e.g. when `~select.epoll` is available,
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always use it instead of `~select.select`), or when a
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previously-monolithic class has been split into specialized
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subclasses.
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Configurable subclasses must define the class methods
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`configurable_base` and `configurable_default`, and use the instance
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method `initialize` instead of ``__init__``.
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"""
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__impl_class = None
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__impl_kwargs = None
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def __new__(cls, **kwargs):
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base = cls.configurable_base()
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args = {}
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if cls is base:
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impl = cls.configured_class()
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if base.__impl_kwargs:
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args.update(base.__impl_kwargs)
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else:
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impl = cls
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args.update(kwargs)
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instance = super(Configurable, cls).__new__(impl)
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# initialize vs __init__ chosen for compatiblity with AsyncHTTPClient
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# singleton magic. If we get rid of that we can switch to __init__
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# here too.
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instance.initialize(**args)
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return instance
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@classmethod
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def configurable_base(cls):
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"""Returns the base class of a configurable hierarchy.
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This will normally return the class in which it is defined.
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(which is *not* necessarily the same as the cls classmethod parameter).
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"""
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raise NotImplementedError()
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@classmethod
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def configurable_default(cls):
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"""Returns the implementation class to be used if none is configured."""
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raise NotImplementedError()
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def initialize(self):
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"""Initialize a `Configurable` subclass instance.
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Configurable classes should use `initialize` instead of ``__init__``.
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"""
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@classmethod
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def configure(cls, impl, **kwargs):
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"""Sets the class to use when the base class is instantiated.
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Keyword arguments will be saved and added to the arguments passed
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to the constructor. This can be used to set global defaults for
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some parameters.
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"""
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base = cls.configurable_base()
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if isinstance(impl, (unicode_type, bytes_type)):
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impl = import_object(impl)
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if impl is not None and not issubclass(impl, cls):
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raise ValueError("Invalid subclass of %s" % cls)
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base.__impl_class = impl
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base.__impl_kwargs = kwargs
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@classmethod
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def configured_class(cls):
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"""Returns the currently configured class."""
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base = cls.configurable_base()
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if cls.__impl_class is None:
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base.__impl_class = cls.configurable_default()
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return base.__impl_class
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@classmethod
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def _save_configuration(cls):
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base = cls.configurable_base()
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return (base.__impl_class, base.__impl_kwargs)
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@classmethod
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def _restore_configuration(cls, saved):
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base = cls.configurable_base()
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base.__impl_class = saved[0]
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base.__impl_kwargs = saved[1]
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class ArgReplacer(object):
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"""Replaces one value in an ``args, kwargs`` pair.
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Inspects the function signature to find an argument by name
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whether it is passed by position or keyword. For use in decorators
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and similar wrappers.
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"""
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def __init__(self, func, name):
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self.name = name
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try:
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self.arg_pos = inspect.getargspec(func).args.index(self.name)
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except ValueError:
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# Not a positional parameter
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self.arg_pos = None
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def replace(self, new_value, args, kwargs):
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"""Replace the named argument in ``args, kwargs`` with ``new_value``.
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Returns ``(old_value, args, kwargs)``. The returned ``args`` and
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``kwargs`` objects may not be the same as the input objects, or
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the input objects may be mutated.
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If the named argument was not found, ``new_value`` will be added
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to ``kwargs`` and None will be returned as ``old_value``.
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"""
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if self.arg_pos is not None and len(args) > self.arg_pos:
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# The arg to replace is passed positionally
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old_value = args[self.arg_pos]
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args = list(args) # *args is normally a tuple
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args[self.arg_pos] = new_value
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else:
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# The arg to replace is either omitted or passed by keyword.
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old_value = kwargs.get(self.name)
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kwargs[self.name] = new_value
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return old_value, args, kwargs
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def doctests():
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import doctest
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return doctest.DocTestSuite()
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