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# -*- coding: utf-8 -*-
This implements a hack to support packages in multiple versions running
side by side in Python. It is supported by the language and as such
should work on any conforming Python interpreter.
The downside is that this bypasses meta hooks so it will only be able
to import regular modules, c extensions and modules can can be found
with the help of a path hook.
:copyright: (c) Copyright 2011 by Armin Ronacher.
:license: BSD, see LICENSE for more details.
import os
import sys
import imp
import binascii
import weakref
from types import ModuleType
import __builtin__
actual_import = __builtin__.__import__
space = imp.new_module('')
space.__path__ = []
sys.modules[space.__name__] = space
class ModuleProxy(ModuleType):
"""Used to proxy to an actual module. This is needed because many
people do `__import__` + a lookup in sys.modules.
def __init__(self, name):
ModuleType.__init__(self, name)
def __getattr__(self, name):
mod = get_actual_module(self.__name__, stacklevel=2)
if mod is None:
raise AttributeError(name)
return getattr(mod, name)
def __setattr__(self, name, value):
mod = get_actual_module(self.__name__, stacklevel=2)
if mod is None:
raise AttributeError(name)
return setattr(mod, name, value)
def get_actual_module(name, stacklevel=1):
"""From the caller's view this returns the actual module that was
requested for a given name.
globals = sys._getframe(stacklevel).f_globals
cache_key = get_cache_key(name, globals)
if cache_key is not None:
full_name = '%s.%s' % (get_internal_name(cache_key), name)
return sys.modules[full_name]
def require_version(library, version, globals=None):
"""Has to be callde at toplevel before importing a module to notify
the multiversion system about the version that should be loaded for
this particular library.
if globals is None:
frm = sys._getframe(1)
if frm.f_globals is not frm.f_locals:
raise RuntimeError('version requirements must happen toplevel')
globals = frm.f_globals
mapping = globals.setdefault('__multiversion_mapping__', {})
if library in mapping:
raise RuntimeError('requirement already specified')
mapping[library] = version
# shortcut :)
require = require_version
def version_from_module_name(module):
"""Extracts the package and version information from the given internal
module name. If it's not a versioned library it will return `None`.
if not module.startswith(space.__name__ + '.'):
return None
result = module[len(space.__name__) + 1].split('.', 1)
if len(result) == 2 and '___' in result[1]:
return binascii.unhexlify(result[1].rsplit('___', 1)[1])
def get_cache_key(name, globals):
"""Returns the cache key for the given module. The globals dictionary
is required for the magic to work. It's used as source for the package
name. The cache key is in the format ``(package, version)``. If the
given import is not versioned it will return `None`.
mapping = globals.get('__multiversion_mapping__')
if mapping is None:
package = name.split('.', 1)[0]
version = mapping.get(package)
if version is None:
version = version_from_module_name(globals.get('__name__'))
if version is None:
return package, version
def get_internal_name(cache_key):
"""Converts a cache key into an internal space module name."""
package, version = cache_key
return '' % (package, binascii.hexlify(version))
def rewrite_import_name(name, cache_key):
"""Rewrites a whole import line according to the cache key."""
return '%s.%s' % (get_internal_name(cache_key), name)
def version_not_loaded(cache_key):
"""Checks if the given module and version was not loaded so far."""
internal_name = get_internal_name(cache_key)
return sys.modules.get(internal_name) is None
def load_version(cache_key):
"""Loads a version of a module. Will raise `ImportError` if it fails
doing so.
fs_name = '%s-%s' % cache_key
internal_name = get_internal_name(cache_key)
for path_entry in sys.path:
full_path = os.path.join(path_entry, fs_name)
if not os.path.isdir(full_path):
mod = imp.new_module(internal_name)
setattr(space, internal_name.rsplit('.', 1)[1], mod)
mod.__path__ = [full_path]
sys.modules[mod.__name__] = mod
raise ImportError('Version %r of %r not found' % cache_key[::-1])
def version_import(name, globals=None, locals=None, fromlist=None, level=-1):
"""An import hook that performs the versioned import. It can't work
on the level of the regular import hooks as it's actually renaming
if globals is None:
globals = sys._getframe(1).f_globals
if locals is None:
locals = {}
if fromlist is None:
fromlist = []
key = get_cache_key(name, globals)
actual_name = name
if key is not None:
actual_name = rewrite_import_name(actual_name, key)
if version_not_loaded(key):
if not fromlist:
fromlist = ['__name__']
rv = actual_import(actual_name, globals, locals, fromlist, level)
proxy = sys.modules.get(name)
if proxy is None:
rv.__multiversion_proxy__ = proxy = ModuleProxy(name)
def cleanup_proxy(ref):
sys.modules.pop(name, None)
except (TypeError, AttributeError):
sys.modules[name] = weakref.proxy(proxy, cleanup_proxy)
return rv
__builtin__.__import__ = version_import
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