mercurial/demandload.py
author Thomas Arendsen Hein <thomas@intevation.de>
Sat, 01 Apr 2006 21:37:08 +0200
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Group changes done by the same developer on the same with --style=changelog Changeset and tags are appended to the change message for non-quiet and non-verbose output, so grouping works. Fixes last bit of issue110.
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'''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)