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# Copyright 2009 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
# $Id$
__all__ = ['lazy_import']
import sys
import types
from portage.proxy.objectproxy import ObjectProxy
class _LazyImport(ObjectProxy):
__slots__ = ('_scope', '_alias', '_name', '_target')
def __init__(self, scope, alias, name):
ObjectProxy.__init__(self)
object.__setattr__(self, '_scope', scope)
object.__setattr__(self, '_alias', alias)
object.__setattr__(self, '_name', name)
def _get_target(self):
try:
return object.__getattribute__(self, '_target')
except AttributeError:
pass
name = object.__getattribute__(self, '_name')
__import__(name)
target = sys.modules[name]
object.__setattr__(self, '_target', target)
object.__getattribute__(self, '_scope')[
object.__getattribute__(self, '_alias')] = target
return target
class _LazyImportFrom(_LazyImport):
__slots__ = ()
def _get_target(self):
try:
return object.__getattribute__(self, '_target')
except AttributeError:
pass
name = object.__getattribute__(self, '_name')
components = name.split('.')
parent_name = '.'.join(components[:-1])
__import__(parent_name)
target = getattr(sys.modules[parent_name], components[-1])
object.__setattr__(self, '_target', target)
object.__getattribute__(self, '_scope')[
object.__getattribute__(self, '_alias')] = target
return target
def lazyimport(scope, *args):
"""
Create a proxy in the given scope in order to performa a lazy import.
Syntax Result
foo import foo
foo:bar,baz from foo import bar, baz
foo:bar@baz from foo import bar as baz
@param scope: the scope in which to place the import, typically globals()
@type myfilename: dict
@param args: module names to import
@type args: strings
"""
modules = sys.modules
for s in args:
parts = s.split(':', 1)
if len(parts) == 1:
name = s
if not name or not isinstance(name, basestring):
raise ValueError(name)
components = name.split('.')
parent_scope = scope
for i in xrange(len(components)):
alias = components[i]
if i < len(components) - 1:
parent_name = ".".join(components[:i+1])
__import__(parent_name)
mod = modules.get(parent_name)
if not isinstance(mod, types.ModuleType):
# raise an exception
__import__(name)
parent_scope[alias] = mod
parent_scope = mod.__dict__
continue
already_imported = modules.get(name)
if already_imported is not None:
parent_scope[alias] = already_imported
else:
parent_scope[alias] = \
_LazyImport(parent_scope, alias, name)
else:
name, fromlist = parts
already_imported = modules.get(name)
fromlist = fromlist.split(',')
for s in fromlist:
alias = s.split('@', 1)
if len(alias) == 1:
alias = alias[0]
orig = alias
else:
orig, alias = alias
if already_imported is not None:
try:
scope[alias] = getattr(already_imported, orig)
except AttributeError:
raise ImportError('cannot import name %s' % orig)
else:
scope[alias] = _LazyImportFrom(scope, alias,
name + '.' + orig)
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