'''Demand load modules when used, not when imported.'''
__author__ = '''Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>.
This software may be used and distributed according to the terms
of the GNU General Public License, incorporated herein by reference.'''
# this is based on matt's original demandload module. it is a
# complete rewrite. some time, we may need to support syntax of
# "import foo as bar".
class _importer(object):
'''import a module. it is not imported until needed, and is
imported at most once per scope.'''
def __init__(self, scope, modname, fromlist):
'''scope is context (globals() or locals()) in which import
should be made. modname is name of module to import.
fromlist is list of modules for "from foo import ..."
emulation.'''
self.scope = scope
self.modname = modname
self.fromlist = fromlist
self.mod = None
def module(self):
'''import the module if needed, and return.'''
if self.mod is None:
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 as 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 = []
as_ = None
if '@' in mod:
mod, as_ = mod.split("@")
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
if not as_:
as_ = basemod
scope[as_] = _replacer(importer, as_)