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146 lines
4.5 KiB
Python
146 lines
4.5 KiB
Python
5 years ago
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# This module is from mx/DateTime/LazyModule.py and is
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# distributed under the terms of the eGenix.com Public License Agreement
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# http://www.egenix.com/products/eGenix.com-Public-License-1.1.0.pdf
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""" Helper to enable simple lazy module import.
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'Lazy' means the actual import is deferred until an attribute is
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requested from the module's namespace. This has the advantage of
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allowing all imports to be done at the top of a script (in a
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prominent and visible place) without having a great impact
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on startup time.
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Copyright (c) 1999-2005, Marc-Andre Lemburg; mailto:mal@lemburg.com
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See the documentation for further information on copyrights,
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or contact the author. All Rights Reserved.
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"""
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from __future__ import print_function
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### Constants
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_debug = 0
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###
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class LazyModule:
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""" Lazy module class.
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Lazy modules are imported into the given namespaces whenever a
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non-special attribute (there are some attributes like __doc__
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that class instances handle without calling __getattr__) is
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requested. The module is then registered under the given name
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in locals usually replacing the import wrapper instance. The
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import itself is done using globals as global namespace.
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Example of creating a lazy load module:
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ISO = LazyModule('ISO',locals(),globals())
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Later, requesting an attribute from ISO will load the module
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automatically into the locals() namespace, overriding the
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LazyModule instance:
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t = ISO.Week(1998,1,1)
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"""
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# Flag which inidicates whether the LazyModule is initialized or not
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__lazymodule_init = 0
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# Name of the module to load
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__lazymodule_name = ''
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# Flag which indicates whether the module was loaded or not
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__lazymodule_loaded = 0
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# Locals dictionary where to register the module
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__lazymodule_locals = None
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# Globals dictionary to use for the module import
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__lazymodule_globals = None
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def __init__(self, name, locals, globals=None):
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""" Create a LazyModule instance wrapping module name.
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The module will later on be registered in locals under the
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given module name.
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globals is optional and defaults to locals.
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"""
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self.__lazymodule_locals = locals
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if globals is None:
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globals = locals
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self.__lazymodule_globals = globals
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mainname = globals.get('__name__', '')
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if mainname:
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self.__name__ = mainname + '.' + name
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self.__lazymodule_name = name
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else:
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self.__name__ = self.__lazymodule_name = name
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self.__lazymodule_init = 1
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def __lazymodule_import(self):
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""" Import the module now.
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"""
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# Load and register module
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name = self.__lazymodule_name
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if self.__lazymodule_loaded:
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return self.__lazymodule_locals[name]
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if _debug:
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print('LazyModule: Loading module %r' % name)
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self.__lazymodule_locals[name] = module = __import__(
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name, self.__lazymodule_locals, self.__lazymodule_globals, '*'
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)
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# Fill namespace with all symbols from original module to
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# provide faster access.
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self.__dict__.update(module.__dict__)
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# Set import flag
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self.__dict__['__lazymodule_loaded'] = 1
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if _debug:
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print('LazyModule: Module %r loaded' % name)
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return module
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def __getattr__(self, name):
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""" Import the module on demand and get the attribute.
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"""
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if self.__lazymodule_loaded:
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raise AttributeError(name)
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if _debug:
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print(
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'LazyModule: '
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'Module load triggered by attribute %r read access' % name
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)
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module = self.__lazymodule_import()
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return getattr(module, name)
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def __setattr__(self, name, value):
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""" Import the module on demand and set the attribute.
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"""
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if not self.__lazymodule_init:
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self.__dict__[name] = value
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return
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if self.__lazymodule_loaded:
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self.__lazymodule_locals[self.__lazymodule_name] = value
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self.__dict__[name] = value
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return
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if _debug:
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print(
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'LazyModule: '
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'Module load triggered by attribute %r write access' % name
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)
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module = self.__lazymodule_import()
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setattr(module, name, value)
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def __repr__(self):
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return "<LazyModule '%s'>" % self.__name__
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