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# Copyright (C) 2010 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
"""General Python convenience functions."""
from __future__ import absolute_import
import sys
def get_named_object(module_name, member_name=None):
"""Get the Python object named by a given module and member name.
This is usually much more convenient than dealing with ``__import__``
directly::
>>> doc = get_named_object('bzrlib.pyutils', 'get_named_object.__doc__')
>>> doc.splitlines()[0]
'Get the Python object named by a given module and member name.'
:param module_name: a module name, as would be found in sys.modules if
the module is already imported. It may contain dots. e.g. 'sys' or
'os.path'.
:param member_name: (optional) a name of an attribute in that module to
return. It may contain dots. e.g. 'MyClass.some_method'. If not
given, the named module will be returned instead.
:raises: ImportError or AttributeError.
"""
# We may have just a module name, or a module name and a member name,
# and either may contain dots. __import__'s return value is a bit
# unintuitive, so we need to take care to always return the object
# specified by the full combination of module name + member name.
if member_name:
# Give __import__ a from_list. It will return the last module in
# the dotted module name.
attr_chain = member_name.split('.')
from_list = attr_chain[:1]
obj = __import__(module_name, {}, {}, from_list)
for attr in attr_chain:
obj = getattr(obj, attr)
else:
# We're just importing a module, no attributes, so we have no
# from_list. __import__ will return the first module in the dotted
# module name, so we look up the module from sys.modules.
__import__(module_name, globals(), locals(), [])
obj = sys.modules[module_name]
return obj
def calc_parent_name(module_name, member_name=None):
"""Determine the 'parent' of a given dotted module name and (optional)
member name.
The idea is that ``getattr(parent_obj, final_attr)`` will equal
get_named_object(module_name, member_name).
:return: (module_name, member_name, final_attr) tuple.
"""
# +SKIP is not recognized by python2.4
# Typical use is::
#
# >>> parent_mod, parent_member, final_attr = calc_parent_name(
# ... module_name, member_name) # doctest: +SKIP
# >>> parent_obj = get_named_object(parent_mod, parent_member)
# ... # doctest: +SKIP
if member_name is not None:
split_name = member_name.rsplit('.', 1)
if len(split_name) == 1:
return (module_name, None, member_name)
else:
return (module_name, split_name[0], split_name[1])
else:
split_name = module_name.rsplit('.', 1)
if len(split_name) == 1:
raise AssertionError(
'No parent object for top-level module %r' % (module_name,))
else:
return (split_name[0], None, split_name[1])
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