annotate mercurial/demandimport.py @ 11942:50a4e55aa278

demandimport: store level argument on _demandmod instances

The 'level' argument to __import__ was added in Python 2.6, and is
specified for either relative or absolute imports. The fix introduced
in e160f2312815 allowed such imports to proceed without failure, but
effectively disabled demandimport for them. This is particularly
unfortunate in Python 3.x, where *all* imports are either relative or
absolute.

The solution introduced here is to store the level argument on the
demandimport instance, and propagate it to _origimport() when its
value isn't None.

Please note that this patch hasn't been tested in Python 3.x, and thus
may not be complete. I'm worried about how sub-imports are handled; I
don't know what they are, or whether the level argument should be
modified for them. I've added 'TODO' notes to these cases; hopefully,
someone more knowledgable of these issues will deal with them.

# demandimport.py - global demand-loading of modules for Mercurial
#
# Copyright 2006, 2007 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

'''
demandimport - automatic demandloading of modules

To enable this module, do:

  import demandimport; demandimport.enable()

Imports of the following forms will be demand-loaded:

  import a, b.c
  import a.b as c
  from a import b,c # a will be loaded immediately

These imports will not be delayed:

  from a import *
  b = __import__(a)
'''

import __builtin__
_origimport = __import__

class _demandmod(object):
    """module demand-loader and proxy"""
    def __init__(self, name, globals, locals, level):
        if '.' in name:
            head, rest = name.split('.', 1)
            after = [rest]
        else:
            head = name
            after = []
        object.__setattr__(self, "_data", (head, globals, locals, after, level))
        object.__setattr__(self, "_module", None)
    def _extend(self, name):
        """add to the list of submodules to load"""
        self._data[3].append(name)
    def _load(self):
        if not self._module:
            head, globals, locals, after, level = self._data
            if level is not None:
                mod = _origimport(head, globals, locals, level)
            else:
                mod = _origimport(head, globals, locals)
            # load submodules
            def subload(mod, p):
                h, t = p, None
                if '.' in p:
                    h, t = p.split('.', 1)
                if not hasattr(mod, h):
                    # TODO: should we adjust the level here?
                    submod = _demandmod(p, mod.__dict__, mod.__dict__,
                                        level=level)
                    setattr(mod, h, submod)
                elif t:
                    subload(getattr(mod, h), t)

            for x in after:
                subload(mod, x)

            # are we in the locals dictionary still?
            if locals and locals.get(head) == self:
                locals[head] = mod
            object.__setattr__(self, "_module", mod)

    def __repr__(self):
        if self._module:
            return "<proxied module '%s'>" % self._data[0]
        return "<unloaded module '%s'>" % self._data[0]
    def __call__(self, *args, **kwargs):
        raise TypeError("%s object is not callable" % repr(self))
    def __getattribute__(self, attr):
        if attr in ('_data', '_extend', '_load', '_module'):
            return object.__getattribute__(self, attr)
        self._load()
        return getattr(self._module, attr)
    def __setattr__(self, attr, val):
        self._load()
        setattr(self._module, attr, val)

def _demandimport(name, globals=None, locals=None, fromlist=None, level=None):
    if not locals or name in ignore or fromlist == ('*',):
        # these cases we can't really delay
        if level is None:
            return _origimport(name, globals, locals, fromlist)
        else:
            return _origimport(name, globals, locals, fromlist, level)
    elif not fromlist:
        # import a [as b]
        if '.' in name: # a.b
            base, rest = name.split('.', 1)
            # email.__init__ loading email.mime
            if globals and globals.get('__name__', None) == base:
                if level is not None:
                    return _origimport(name, globals, locals, fromlist, level)
                else:
                    return _origimport(name, globals, locals, fromlist)
            # if a is already demand-loaded, add b to its submodule list
            if base in locals:
                if isinstance(locals[base], _demandmod):
                    locals[base]._extend(rest)
                return locals[base]
        return _demandmod(name, globals, locals, level=level)
    else:
        # from a import b,c,d
        if level is not None:
            mod = _origimport(name, globals, locals, level=level)
        else:
            mod = _origimport(name, globals, locals)
        # recurse down the module chain
        for comp in name.split('.')[1:]:
            if not hasattr(mod, comp):
                # TODO: should we adjust the level here?
                submod = _demandmod(comp, mod.__dict__, mod.__dict__,
                                    level=level)
                setattr(mod, comp, submod)
            mod = getattr(mod, comp)
        for x in fromlist:
            # set requested submodules for demand load
            if not(hasattr(mod, x)):
                # TODO: should we adjust the level here?
                submod = _demandmod(x, mod.__dict__, locals, level=level)
                setattr(mod, x, submod)
        return mod

ignore = [
    '_hashlib',
    '_xmlplus',
    'fcntl',
    'win32com.gen_py',
    '_winreg', # 2.7 mimetypes needs immediate ImportError
    'pythoncom',
    # imported by tarfile, not available under Windows
    'pwd',
    'grp',
    # imported by profile, itself imported by hotshot.stats,
    # not available under Windows
    'resource',
    # this trips up many extension authors
    'gtk',
    # setuptools' pkg_resources.py expects "from __main__ import x" to
    # raise ImportError if x not defined
    '__main__',
    '_ssl', # conditional imports in the stdlib, issue1964
    ]

def enable():
    "enable global demand-loading of modules"
    __builtin__.__import__ = _demandimport

def disable():
    "disable global demand-loading of modules"
    __builtin__.__import__ = _origimport