from functools import partial
# This definition is only used to assist static code analyzers
def copy_ancestor_docstring(fn):
'''Copy docstring for method from superclass
For this decorator to work, the class has to use the `InheritableDocstrings`
metaclass.
'''
raise RuntimeError('Decorator can only be used in classes '
'using the `InheritableDocstrings` metaclass')
def _copy_ancestor_docstring(mro, fn):
'''Decorator to set docstring for *fn* from *mro*'''
if fn.__doc__ is not None:
raise RuntimeError('Function already has docstring')
# Search for docstring in superclass
for cls in mro:
super_fn = getattr(cls, fn.__name__, None)
if super_fn is None:
continue
fn.__doc__ = super_fn.__doc__
break
else:
raise RuntimeError("Can't inherit docstring for %s: method does not "
"exist in superclass" % fn.__name__)
return fn
class InheritableDocstrings(type):
@classmethod
def __prepare__(cls, name, bases, **kwds):
classdict = super().__prepare__(name, bases, *kwds)
# Construct temporary dummy class to figure out MRO
mro = type('K', bases, {}).__mro__[1:]
assert mro[-1] == object
mro = mro[:-1]
# Inject decorators into class namespace
classdict['copy_ancestor_docstring'] = partial(_copy_ancestor_docstring, mro)
return classdict
def __new__(cls, name, bases, classdict):
# Make sure that class definition hasn't messed with decorators
copy_impl = getattr(classdict['copy_ancestor_docstring'], 'func', None)
if copy_impl is not _copy_ancestor_docstring:
raise RuntimeError('No copy_ancestor_docstring attribute may be created '
'in classes using the InheritableDocstrings metaclass')
# Delete decorators from class namespace
del classdict['copy_ancestor_docstring']
return super().__new__(cls, name, bases, classdict)
