"""Routines to support optional packages."""
import importlib
try:
import pytest
except ImportError:
have_pytest = False
else:
have_pytest = True
class TripWireError(AttributeError):
"""Exception if trying to use TripWire object."""
def is_tripwire(obj):
"""Return True if `obj` appears to be a TripWire object.
Examples
--------
>>> is_tripwire(object())
False
>>> is_tripwire(TripWire('some message'))
True
"""
try:
obj.any_attribute
except TripWireError:
return True
except Exception:
pass
return False
class TripWire(object):
"""Class raising error if used.
Standard use is to proxy modules that we could not import
Examples
--------
>>> try:
... import silly_module_name
... except ImportError:
... silly_module_name = TripWire('We do not have silly_module_name')
>>> silly_module_name.do_silly_thing('with silly string') #doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
TripWireError: We do not have silly_module_name
"""
def __init__(self, msg):
self._msg = msg
def __getattr__(self, attr_name):
"""Raise informative error accessing attributes."""
raise TripWireError(self._msg)
def __call__(self, *args, **kwargs):
"""Raise informative error while calling."""
raise TripWireError(self._msg)
[docs]def optional_package(name, trip_msg=None):
"""Return package-like thing and module setup for package `name`.
Parameters
----------
name : str
package name
trip_msg : None or str
message to give when someone tries to use the return package, but we
could not import it, and have returned a TripWire object instead.
Default message if None.
Returns
-------
pkg_like : module or ``TripWire`` instance
If we can import the package, return it. Otherwise return an object
raising an error when accessed
have_pkg : bool
True if import for package was successful, false otherwise
module_setup : function
callable usually set as ``setup_module`` in calling namespace, to allow
skipping tests.
Examples
--------
Typical use would be something like this at the top of a module using an
optional package:
>>> from fury.optpkg import optional_package
>>> pkg, have_pkg, setup_module = optional_package('not_a_package')
Of course in this case the package doesn't exist, and so, in the module:
>>> have_pkg
False
and
>>> pkg.some_function() #doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
TripWireError: We need package not_a_package for these functions, but
``import not_a_package`` raised an ImportError
If the module does exist - we get the module
>>> pkg, _, _ = optional_package('os')
>>> hasattr(pkg, 'path')
True
Or a submodule if that's what we asked for
>>> subpkg, _, _ = optional_package('os.path')
>>> hasattr(subpkg, 'dirname')
True
"""
try:
pkg = importlib.import_module(name)
except ImportError:
pass
else: # import worked
# top level module
return pkg, True, lambda: None
if trip_msg is None:
trip_msg = ('We need package %s for these functions, but '
'``import %s`` raised an ImportError'
% (name, name))
pkg = TripWire(trip_msg)
def setup_module():
if have_pytest:
pytest.mark.skip('No {0} for these tests'.format(name))
return pkg, False, setup_module