mercurial/demandimport.py
author Brendan Cully <brendan@kublai.com>
Sat, 03 Mar 2007 18:59:54 -0800
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# demandimport.py - global demand-loading of modules for Mercurial
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#
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# Copyright 2006 Matt Mackall <mpm@selenic.com>
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#
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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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'''
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demandimport - automatic demandloading of modules
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To enable this module, do:
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  import demandimport; demandimport.enable()
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Imports of the following forms will be demand-loaded:
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  import a, b.c
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  import a.b as c
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  from a import b,c # a will be loaded immediately
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These imports will not be delayed:
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  from a import *
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  b = __import__(a)
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'''
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_origimport = __import__
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class _demandmod(object):
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    """module demand-loader and proxy"""
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    def __init__(self, name, globals, locals):
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        if '.' in name:
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            head, rest = name.split('.', 1)
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            after = [rest]
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        else:
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            head = name
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            after = []
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        object.__setattr__(self, "_data", (head, globals, locals, after))
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        object.__setattr__(self, "_module", None)
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    def _extend(self, name):
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        """add to the list of submodules to load"""
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        self._data[3].append(name)
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    def _load(self):
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        if not self._module:
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            head, globals, locals, after = self._data
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            mod = _origimport(head, globals, locals)
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            # load submodules
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            def subload(mod, p):
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                h, t = p, None
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                if '.' in p:
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                    h, t = p.split('.', 1)
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                if not hasattr(mod, h):
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                    setattr(mod, h, _demandmod(p, mod.__dict__, mod.__dict__))
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                elif t:
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                    subload(getattr(mod, h), t)
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            for x in after:
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                subload(mod, x)
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            # are we in the locals dictionary still?
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            if locals and locals.get(head) == self:
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                locals[head] = mod
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            object.__setattr__(self, "_module", mod)
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    def __repr__(self):
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        return "<unloaded module '%s'>" % self._data[0]
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    def __call__(self, *args, **kwargs):
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        raise TypeError("'unloaded module' object is not callable")
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    def __getattribute__(self, attr):
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        if attr in ('_data', '_extend', '_load', '_module'):
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            return object.__getattribute__(self, attr)
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        self._load()
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        return getattr(self._module, attr)
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    def __setattr__(self, attr, val):
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        self._load()
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        setattr(self._module, attr, val)
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def _demandimport(name, globals=None, locals=None, fromlist=None):
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    if not locals or name in ignore or fromlist == ('*',):
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        # these cases we can't really delay
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        return _origimport(name, globals, locals, fromlist)
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    elif not fromlist:
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        # import a [as b]
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        if '.' in name: # a.b
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            base, rest = name.split('.', 1)
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            # email.__init__ loading email.mime
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            if globals and globals.get('__name__', None) == base:
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                return _origimport(name, globals, locals, fromlist)
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            # if a is already demand-loaded, add b to its submodule list
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            if base in locals:
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                if isinstance(locals[base], _demandmod):
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                    locals[base]._extend(rest)
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                return locals[base]
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        return _demandmod(name, globals, locals)
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    else:
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        # from a import b,c,d
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        mod = _origimport(name, globals, locals)
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        # recurse down the module chain
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        for comp in name.split('.')[1:]:
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            mod = getattr(mod, comp)
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        for x in fromlist:
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            # set requested submodules for demand load
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            if not(hasattr(mod, x)):
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                setattr(mod, x, _demandmod(x, mod.__dict__, mod.__dict__))
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        return mod
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ignore = ['_hashlib', '_xmlplus', 'fcntl', 'win32com.gen_py']
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def enable():
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    "enable global demand-loading of modules"
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    __builtins__["__import__"] = _demandimport
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def disable():
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    "disable global demand-loading of modules"
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    __builtins__["__import__"] = _origimport
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