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5436.2.1
by Andrew Bennetts
Add bzrlib.pyutils, which has get_named_object, a wrapper around __import__. |
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# Copyright (C) 2010 Canonical Ltd
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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"""Some convenience functions for general Python, such as a wrapper around
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``_import__``.
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"""
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import sys |
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def get_named_object(module_name, member_name=None): |
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"""Get the Python object named by a given module and member name.
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This is usually much more convenient than dealing with ``__import__``
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directly.
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:param module_name: a module name, as found in sys.module. It may contain
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dots. e.g. 'sys' or 'os.path'.
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:param member_name: (optional) a name of an attribute in that module to
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return. It may contain dots. e.g. 'MyClass.some_method'. If not
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given, the named module will be returned instead.
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:raises: ImportError or AttributeError.
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"""
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# We may have just a module name, or a module name and a member name,
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# and either may contain dots. __import__'s return value is a bit
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# unintuitive, so we need to take care to always return the object
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# specified by the full combination of module name + member name.
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if member_name: |
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# Give __import__ a from_list. It will return the last module in
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# the dotted module name.
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attr_chain = member_name.split('.') |
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from_list = attr_chain[:1] |
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obj = __import__(module_name, {}, {}, from_list) |
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for attr in attr_chain: |
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obj = getattr(obj, attr) |
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else: |
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# We're just importing a module, no attributes, so we have no
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# from_list. __import__ will return the first module in the dotted
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# module name, so we look up the module from sys.modules.
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__import__(module_name, globals(), locals(), []) |
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obj = sys.modules[module_name] |
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return obj |
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def calc_parent_name(module_name, member_name=None): |
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"""Determine the 'parent' of a given dotted module name and (optional)
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member name.
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Typical use is::
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>>> parent_mod, parent_member, final_attr = calc_parent_name(
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... module_name, member_name)
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>>> parent_obj = get_named_object(parent_mod, parent_member)
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The idea is that ``getattr(parent_obj, final_attr)`` will equal
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get_named_object(module_name, member_name).
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:return: (module_name, member_name, final_attr) tuple.
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"""
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if member_name is not None: |
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split_name = member_name.rsplit('.', 1) |
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if len(split_name) == 1: |
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return (module_name, None, member_name) |
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else: |
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return (module_name, split_name[0], split_name[1]) |
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else: |
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split_name = module_name.rsplit('.', 1) |
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if len(split_name) == 1: |
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raise AssertionError( |
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'No parent object for top-level module %r' % (module_name,)) |
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else: |
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return (split_name[0], None, split_name[1]) |