mirror of
https://github.com/facebook/sapling.git
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8e12396738
performance not affected. old demandload module could only import top-level modules like os and sys. with rewrite, all of following syntax is emulated perfectly: import foo, bar foo bar import foo.bar.quux foo.bar.quux from foo.bar import quux, blurfl foo.bar:quux,blurfl only thing missing is "import foo as bar". also, namespace clashes between placeholder object and demand loaded module are no longer possible.
126 lines
4.5 KiB
Python
126 lines
4.5 KiB
Python
'''Demand load modules when used, not when imported.'''
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__author__ = '''Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>.
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This software may be used and distributed according to the terms
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of the GNU General Public License, incorporated herein by reference.'''
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# this is based on matt's original demandload module. it is a
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# complete rewrite. some time, we may need to support syntax of
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# "import foo as bar".
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class _importer(object):
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'''import a module. it is not imported until needed, and is
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imported at most once per scope.'''
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def __init__(self, scope, modname, fromlist):
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'''scope is context (globals() or locals()) in which import
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should be made. modname is name of module to import.
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fromlist is list of modules for "from foo import ..."
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emulation.'''
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self.scope = scope
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self.modname = modname
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self.fromlist = fromlist
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self.mod = None
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def module(self):
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'''import the module if needed, and return.'''
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if self.mod is None:
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self.mod = __import__(self.modname, self.scope, self.scope,
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self.fromlist)
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del self.modname, self.fromlist
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return self.mod
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class _replacer(object):
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'''placeholder for a demand loaded module. demandload puts this in
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a target scope. when an attribute of this object is looked up,
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this object is replaced in the target scope with the actual
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module.
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we use __getattribute__ to avoid namespace clashes between
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placeholder object and real module.'''
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def __init__(self, importer, target):
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self.importer = importer
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self.target = target
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# consider case where we do this:
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# demandload(globals(), 'foo.bar foo.quux')
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# foo will already exist in target scope when we get to
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# foo.quux. so we remember that we will need to demandload
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# quux into foo's scope when we really load it.
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self.later = []
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def module(self):
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return object.__getattribute__(self, 'importer').module()
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def __getattribute__(self, key):
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'''look up an attribute in a module and return it. replace the
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name of the module in the caller\'s dict with the actual
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module.'''
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module = object.__getattribute__(self, 'module')()
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target = object.__getattribute__(self, 'target')
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importer = object.__getattribute__(self, 'importer')
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later = object.__getattribute__(self, 'later')
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if later:
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demandload(module.__dict__, ' '.join(later))
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importer.scope[target] = module
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return getattr(module, key)
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class _replacer_from(_replacer):
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'''placeholder for a demand loaded module. used for "from foo
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import ..." emulation. semantics of this are different than
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regular import, so different implementation needed.'''
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def module(self):
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importer = object.__getattribute__(self, 'importer')
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target = object.__getattribute__(self, 'target')
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return getattr(importer.module(), target)
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def demandload(scope, modules):
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'''import modules into scope when each is first used.
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scope should be the value of globals() in the module calling this
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function, or locals() in the calling function.
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modules is a string listing module names, separated by white
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space. names are handled like this:
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foo import foo
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foo bar import foo, bar
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foo.bar import foo.bar
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foo:bar from foo import bar
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foo:bar,quux from foo import bar, quux
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foo.bar:quux from foo.bar import quux'''
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for mod in modules.split():
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col = mod.find(':')
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if col >= 0:
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fromlist = mod[col+1:].split(',')
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mod = mod[:col]
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else:
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fromlist = []
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importer = _importer(scope, mod, fromlist)
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if fromlist:
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for name in fromlist:
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scope[name] = _replacer_from(importer, name)
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else:
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dot = mod.find('.')
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if dot >= 0:
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basemod = mod[:dot]
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val = scope.get(basemod)
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# if base module has already been demandload()ed,
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# remember to load this submodule into its namespace
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# when needed.
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if isinstance(val, _replacer):
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later = object.__getattribute__(val, 'later')
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later.append(mod[dot+1:])
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continue
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else:
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basemod = mod
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scope[basemod] = _replacer(importer, basemod)
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