84 lines
2.7 KiB
Python
84 lines
2.7 KiB
Python
# Copyright (c) 2010-2012 testtools developers. See LICENSE for details.
|
|
|
|
import sys
|
|
|
|
|
|
def try_import(name, alternative=None, error_callback=None):
|
|
"""Attempt to import a module, with a fallback.
|
|
|
|
Attempt to import ``name``. If it fails, return ``alternative``. When
|
|
supporting multiple versions of Python or optional dependencies, it is
|
|
useful to be able to try to import a module.
|
|
|
|
:param name: The name of the object to import, e.g. ``os.path`` or
|
|
``os.path.join``.
|
|
:param alternative: The value to return if no module can be imported.
|
|
Defaults to None.
|
|
:param error_callback: If non-None, a callable that is passed the
|
|
ImportError when the module cannot be loaded.
|
|
"""
|
|
module_segments = name.split('.')
|
|
last_error = None
|
|
remainder = []
|
|
|
|
# module_name will be what successfully imports. We cannot walk from the
|
|
# __import__ result because in import loops (A imports A.B, which imports
|
|
# C, which calls try_import("A.B")) A.B will not yet be set.
|
|
while module_segments:
|
|
module_name = '.'.join(module_segments)
|
|
try:
|
|
__import__(module_name)
|
|
except ImportError:
|
|
last_error = sys.exc_info()[1]
|
|
remainder.append(module_segments.pop())
|
|
continue
|
|
else:
|
|
break
|
|
else:
|
|
if last_error is not None and error_callback is not None:
|
|
error_callback(last_error)
|
|
return alternative
|
|
|
|
module = sys.modules[module_name]
|
|
nonexistent = object()
|
|
for segment in reversed(remainder):
|
|
module = getattr(module, segment, nonexistent)
|
|
if module is nonexistent:
|
|
if last_error is not None and error_callback is not None:
|
|
error_callback(last_error)
|
|
return alternative
|
|
|
|
return module
|
|
|
|
|
|
def map_values(function, dictionary):
|
|
"""Map ``function`` across the values of ``dictionary``.
|
|
|
|
:return: A dict with the same keys as ``dictionary``, where the value
|
|
of each key ``k`` is ``function(dictionary[k])``.
|
|
"""
|
|
return {k: function(dictionary[k]) for k in dictionary}
|
|
|
|
|
|
def filter_values(function, dictionary):
|
|
"""Filter ``dictionary`` by its values using ``function``."""
|
|
return {k: v for k, v in dictionary.items() if function(v)}
|
|
|
|
|
|
def dict_subtract(a, b):
|
|
"""Return the part of ``a`` that's not in ``b``."""
|
|
return {k: a[k] for k in set(a) - set(b)}
|
|
|
|
|
|
def list_subtract(a, b):
|
|
"""Return a list ``a`` without the elements of ``b``.
|
|
|
|
If a particular value is in ``a`` twice and ``b`` once then the returned
|
|
list then that value will appear once in the returned list.
|
|
"""
|
|
a_only = list(a)
|
|
for x in b:
|
|
if x in a_only:
|
|
a_only.remove(x)
|
|
return a_only
|