decorators.rst

Decorators

A functools.wraps() equivalent, but for classes

Preconditions and postconditions

Sometimes you need to specify conditions that parameter to your function will need to obey. You can use the following decorator for this:

And here are some helper functions for it:

has_keys asserts that a dictionary has all the keys necessary.

Use it like this:

>>> @precondition(has_keys(['a', 'b']))
>>> def function(keys):
>>>     ...
>>> function({'a': 5, 'b': 3})
>>> self.assertRaises(PreconditionError, lambda: function({'a': 5}))

short_none is particularly useful with preconditions, or functions that accept a None value as well.

Example:

>>> @precondition(short_none('x == 2'))
>>> def expect_two(x):
>>>     ...
>>> expect_two(None)
>>> expect_two(2)
>>> self.assertRaises(PreconditionError, lambda: expect_two(3))

You can also check the return value with