""" Routines to support optional packages """ try: import nose except ImportError: have_nose = False else: have_nose = True from .tripwire import TripWire 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. Example ------- Typical use would be something like this at the top of a module using an optional package: >>> from nibabel.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 """ # fromlist=[''] results in submodule being returned, rather than the top # level module. See help(__import__) try: pkg = __import__(name, fromlist=['']) 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_nose: raise nose.plugins.skip.SkipTest('No %s for these tests' % name) return pkg, False, setup_module