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view mercurial/demandload.py @ 3239:7a3edd3f7c3e
Install all files/subdirectories below templates.
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author | Thomas Arendsen Hein <thomas@intevation.de> |
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date | Tue, 03 Oct 2006 11:53:35 +0200 |
parents | 61afc32c1a49 |
children |
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'''Demand load modules when used, not when imported.''' __author__ = '''Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>. This software may be used and distributed according to the terms of the GNU General Public License, incorporated herein by reference.''' # this is based on matt's original demandload module. it is a # complete rewrite. some time, we may need to support syntax of # "import foo as bar". class _importer(object): '''import a module. it is not imported until needed, and is imported at most once per scope.''' def __init__(self, scope, modname, fromlist): '''scope is context (globals() or locals()) in which import should be made. modname is name of module to import. fromlist is list of modules for "from foo import ..." emulation.''' self.scope = scope self.modname = modname self.fromlist = fromlist self.mod = None def module(self): '''import the module if needed, and return.''' if self.mod is None: self.mod = __import__(self.modname, self.scope, self.scope, self.fromlist) del self.modname, self.fromlist return self.mod class _replacer(object): '''placeholder for a demand loaded module. demandload puts this in a target scope. when an attribute of this object is looked up, this object is replaced in the target scope with the actual module. we use __getattribute__ to avoid namespace clashes between placeholder object and real module.''' def __init__(self, importer, target): self.importer = importer self.target = target # consider case where we do this: # demandload(globals(), 'foo.bar foo.quux') # foo will already exist in target scope when we get to # foo.quux. so we remember that we will need to demandload # quux into foo's scope when we really load it. self.later = [] def module(self): return object.__getattribute__(self, 'importer').module() def __getattribute__(self, key): '''look up an attribute in a module and return it. replace the name of the module in the caller\'s dict with the actual module.''' module = object.__getattribute__(self, 'module')() target = object.__getattribute__(self, 'target') importer = object.__getattribute__(self, 'importer') later = object.__getattribute__(self, 'later') if later: demandload(module.__dict__, ' '.join(later)) importer.scope[target] = module return getattr(module, key) class _replacer_from(_replacer): '''placeholder for a demand loaded module. used for "from foo import ..." emulation. semantics of this are different than regular import, so different implementation needed.''' def module(self): importer = object.__getattribute__(self, 'importer') target = object.__getattribute__(self, 'target') return getattr(importer.module(), target) def __call__(self, *args, **kwargs): target = object.__getattribute__(self, 'module')() return target(*args, **kwargs) def demandload(scope, modules): '''import modules into scope when each is first used. scope should be the value of globals() in the module calling this function, or locals() in the calling function. modules is a string listing module names, separated by white space. names are handled like this: foo import foo foo bar import foo, bar foo@bar import foo as bar foo.bar import foo.bar foo:bar from foo import bar foo:bar,quux from foo import bar, quux foo.bar:quux from foo.bar import quux''' for mod in modules.split(): col = mod.find(':') if col >= 0: fromlist = mod[col+1:].split(',') mod = mod[:col] else: fromlist = [] as_ = None if '@' in mod: mod, as_ = mod.split("@") importer = _importer(scope, mod, fromlist) if fromlist: for name in fromlist: scope[name] = _replacer_from(importer, name) else: dot = mod.find('.') if dot >= 0: basemod = mod[:dot] val = scope.get(basemod) # if base module has already been demandload()ed, # remember to load this submodule into its namespace # when needed. if isinstance(val, _replacer): later = object.__getattribute__(val, 'later') later.append(mod[dot+1:]) continue else: basemod = mod if not as_: as_ = basemod scope[as_] = _replacer(importer, as_)