UnavailableClass

(function from pyomo.common.dependencies)

pyomo.common.dependencies.UnavailableClass(unavailable_module)

Function to generate an “unavailable” base class

This function returns a custom class that wraps the ModuleUnavailable instance returned by attempt_import() when the target module is not available. Any attempt to instantiate this class (or a class derived from it) or access a class attribute will raise the DeferredImportError from the wrapped ModuleUnavailable object.

Parameters:

unavailable_module (ModuleUnavailable) – The ModuleUnavailable instance (from attempt_import()) to use to generate the DeferredImportError.

Example

Declaring a class that inherits from an optional dependency:

>>> from pyomo.common.dependencies import attempt_import, UnavailableClass
>>> bogus, bogus_available = attempt_import('bogus_unavailable_class')
>>> class MyPlugin(bogus.plugin if bogus_available else UnavailableClass(bogus)):
...     pass

Attempting to instantiate the derived class generates an exception when the module is unavailable:

>>> MyPlugin()
Traceback (most recent call last):
   ...
pyomo.common.dependencies.DeferredImportError: The class 'MyPlugin' cannot be
created because a needed optional dependency was not found (import raised
ModuleNotFoundError: No module named 'bogus_unavailable_class')

As does attempting to access class attributes on the derived class:

>>> MyPlugin.create_instance()
Traceback (most recent call last):
   ...
pyomo.common.dependencies.DeferredImportError: The class attribute
'MyPlugin.create_instance' is not available because a needed optional
dependency was not found (import raised ModuleNotFoundError: No module
named 'bogus_unavailable_class')