1
# Copyright (c) 2010 Jonathan M. Lange. See LICENSE for details.
9
def try_import(name, alternative=None):
10
"""Attempt to import `name`. If it fails, return `alternative`.
12
When supporting multiple versions of Python or optional dependencies, it
13
is useful to be able to try to import a module.
15
:param name: The name of the object to import, e.g. 'os.path' or
17
:param alternative: The value to return if no module can be imported.
20
module_segments = name.split('.')
21
while module_segments:
22
module_name = '.'.join(module_segments)
24
module = __import__(module_name)
32
nonexistent = object()
33
for segment in name.split('.')[1:]:
34
module = getattr(module, segment, nonexistent)
35
if module is nonexistent:
40
_RAISE_EXCEPTION = object()
41
def try_imports(module_names, alternative=_RAISE_EXCEPTION):
42
"""Attempt to import modules.
44
Tries to import the first module in `module_names`. If it can be
45
imported, we return it. If not, we go on to the second module and try
46
that. The process continues until we run out of modules to try. If none
47
of the modules can be imported, either raise an exception or return the
48
provided `alternative` value.
50
:param module_names: A sequence of module names to try to import.
51
:param alternative: The value to return if no module can be imported.
52
If unspecified, we raise an ImportError.
53
:raises ImportError: If none of the modules can be imported and no
54
alternative value was specified.
56
module_names = list(module_names)
57
for module_name in module_names:
58
module = try_import(module_name)
61
if alternative is _RAISE_EXCEPTION:
63
"Could not import any of: %s" % ', '.join(module_names))