Routines to support optional packages

optional_package(name[, trip_msg, min_version])

Return package-like thing and module setup for package name


nibabel.optpkg.optional_package(name, trip_msg=None, min_version=None)

Return package-like thing and module setup for package name


package name

trip_msgNone or str

message to give when someone tries to use the return package, but we could not import it at an acceptable version, and have returned a TripWire object instead. Default message if None.

min_versionNone or str or LooseVersion or callable

If None, do not specify a minimum version. If str, convert to a distutils.version.LooseVersion. If str or LooseVersion` compare to version of package name with min_version <= pkg.__version__. If callable, accepts imported pkg as argument, and returns value of callable is True for acceptable package versions, False otherwise.

pkg_likemodule or TripWire instance

If we can import the package, return it. Otherwise return an object raising an error when accessed


True if import for package was successful, false otherwise


callable usually set as setup_module in calling namespace, to allow skipping tests.


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


>>> pkg.some_function() 
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')

Or a submodule if that’s what we asked for

>>> subpkg, _, _ = optional_package('os.path')
>>> hasattr(subpkg, 'dirname')