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# Copyright (C) 2006 by Canonical Ltd
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""Functionality to create lazy evaluation objects.
This includes waiting to import a module until it is actually used.
"""
import sys
class ScopeReplacer(object):
"""A lazy object that will replace itself in the appropriate scope.
This object sits, ready to create the real object the first time it is
needed.
"""
__slots__ = ('_scope', '_factory', '_name')
def __init__(self, scope, factory, name):
"""Create a temporary object in the specified scope.
Once used, a real object will be placed in the scope.
:param scope: The scope the object should appear in
:param factory: A callable that will create the real object.
It will be passed (self, scope, name)
:param name: The variable name in the given scope.
"""
self._scope = scope
self._factory = factory
self._name = name
scope[name] = self
def _replace(self):
"""Actually replace self with other in the given scope"""
factory = object.__getattribute__(self, '_factory')
scope = object.__getattribute__(self, '_scope')
name = object.__getattribute__(self, '_name')
obj = factory(self, scope, name)
scope[name] = obj
return obj
def _cleanup(self):
"""Stop holding on to all the extra stuff"""
del self._factory
del self._scope
del self._name
def __getattribute__(self, attr):
obj = object.__getattribute__(self, '_replace')()
object.__getattribute__(self, '_cleanup')()
return getattr(obj, attr)
def __call__(self, *args, **kwargs):
obj = object.__getattribute__(self, '_replace')()
object.__getattribute__(self, '_cleanup')()
return obj(*args, **kwargs)
class ImportReplacer(ScopeReplacer):
"""This is designed to replace only a portion of an import list.
It will replace itself with a module, and then make children
entries also ImportReplacer objects.
At present, this only supports 'import foo.bar.baz' syntax.
"""
# Intentially a long semi-unique name that won't likely exist
# elsewhere. (We can't use isinstance because that accesses __class__
# which causes the __getattribute__ to trigger)
__slots__ = ('_import_replacer_children', '_member', '_module_path')
def __init__(self, scope, name, module_path, member=None, children=[]):
"""Upon request import 'module_path' as the name 'module_name'.
When imported, prepare children to also be imported.
:param scope: The scope that objects should be imported into.
Typically this is globals()
:param name: The variable name. Often this is the same as the
module_path. 'bzrlib'
:param module_path: The fully specified dotted path to the module.
'bzrlib.foo.bar'
:param member: The member inside the module to import, often this is
None, indicating the module is being imported.
:param children: Children entries to be imported later.
This should be a list of children specifications.
[('foo', 'bzrlib.foo', [('bar', 'bzrlib.foo.bar'),])]
Examples:
import foo => name='foo' module_path='foo',
member=None, children=[]
import foo.bar => name='foo' module_path='foo', member=None,
children=[('bar', 'foo.bar', [])]
from foo import bar => name='bar' module_path='foo', member='bar'
children=[]
from foo import bar, baz would get translated into 2 import
requests. On for 'name=bar' and one for 'name=baz'
"""
if member is not None:
assert not children, \
'Cannot supply both a member and children'
self._import_replacer_children = children
self._member = member
self._module_path = module_path
ScopeReplacer.__init__(self, scope=scope, name=name,
factory=ImportReplacer._import)
def _import(self, scope, name):
children = object.__getattribute__(self, '_import_replacer_children')
member = object.__getattribute__(self, '_member')
module_path = object.__getattribute__(self, '_module_path')
if member is not None:
module = __import__(module_path, scope, scope, (member,))
return getattr(module, member)
else:
module = __import__(module_path, scope, scope, None)
# Prepare the children to be imported
for child_name, child_path, grandchildren in children:
ImportReplacer(module.__dict__, name=child_name,
module_path=child_path, member=None,
children=grandchildren)
def _replace(self):
"""Actually replace self with other in the given scope"""
factory = object.__getattribute__(self, '_factory')
scope = object.__getattribute__(self, '_scope')
name = object.__getattribute__(self, '_name')
obj = factory()
scope[name] = obj
return obj
class _Importer(object):
"""Helper for importing modules, but waiting until they are used.
This also helps to ensure that existing ScopeReplacer objects are
re-used in the current scope.
"""
__slots__ = ['scope', 'modname', 'fromlist', 'mod']
def __init__(self, scope, modname, fromlist):
"""
:param scope: calling context globals() where the import should be made
:param modname: The name of the module
:param fromlist: the fromlist portion of 'from foo import bar'
"""
self.scope = scope
self.modname = modname
self.fromlist = fromlist
self.mod = None
def module(self):
"""Import a module if not imported yet, and return"""
if self.mod is None:
self.mod = __import__(self.modname, self.scope, self.scope,
self.fromlist)
if isinstance(self.mod, _replacer):
del sys.modules[self.modname]
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.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 = []
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
scope[basemod] = _replacer(importer, basemod)
def lazy_import(scope, module_name, member=None, import_as=None):
"""Lazily import a module into the correct scope.
This is meant as a possible replacement for __import__.
It will return a ScopeReplacer object, which will call the real
'__import__' at the appropriate time.
:param module_name: The dotted module name
:param member: Optional, if supplied return the sub member instead of
the base module.
:param import_as: Use this as the local object name instead of the
default name.
"""
if import_as is None:
if member is None:
module_pieces = module_name.split('.')
final_name = module_pieces[0]
def factory():
return __import__(module_name, scope, locals(), [])
else:
final_name = member
else:
raise NotImplemented('import_as is not yet implemented')
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