contracts package

What follows is an API reference detailing the various functions available in code-contracts.

contracts.assertion module

Module containing code assertions.

It complements the assertions already available in the TestCase class.

contracts.assertion.contains_one_element_of_class(obj_cls, iterable_obj)

Asserts that the specified iterable object contains one and only one element of the specified class.

Parameters:

• obj_cls – the class of the object that is expected to be found in the iterable.
• iterable_obj – Iterable object.

Raises:

AssertionError if the callable does not raise an exception of the specified class.

contracts.assertion.does_not_raise(exception_cls, callable_obj, *args, **kwargs)

Asserts that the specified callable object does not raise an exception of the specified class when called.

Parameters:

• exception_cls – the class of the exception.
• callable_obj – the callable object (function or method).
• args – the positional arguments to pass to the callable.
• kwargs – the keyword arguments to pass to the callable.

Raises:

AssertionError if the callable raises an exception of the specified class.

contracts.assertion.not_called_with(mock_obj, *args, **kwargs)

Asserts that the specified mock object was never called with a specific sequence of arguments.

Acts as a complementary function, because there is no assert_not_called_with() method available in the Mock class.

Parameters:

• mock_obj – Mock object.
• args – the positional arguments to pass to the callable.
• kwargs – the keyword arguments to pass to the callable.

Raises:

AssertionError if the callable does not raise an exception of the specified class.

contracts.assertion.raises(exception_cls, callable_obj, *args, **kwargs)

Asserts that the specified callable object raises an exception of the specified class when called.

Can be used instead of assertRaises() for consistency across unit tests, especially when does_not_raise() is also used.

Parameters:

• exception_cls – the class of the exception.
• callable_obj – the callable object (function or method).
• args – the positional arguments to pass to the callable.
• kwargs – the keyword arguments to pass to the callable.

Raises:

AssertionError if the callable does not raise an exception of the specified class.

contracts.assertion.raises_with_msg(exception_cls, callable_obj, expected_exception_msg, *args, **kwargs)

Asserts that the specified callable object raises an exception of the specified type with the specified message when called.

Parameters:

• exception_cls – the class of the exception.
• callable_obj – the callable object (function or method).
• expected_exception_msg – the expected substring in the exception’s message.
• args – the positional arguments to pass to the callable.
• kwargs – the keyword arguments to pass to the callable.

Raises:

AssertionError if the callable does not raise an exception of the specified class.

contracts.contract module

Module containing code contracts.

contracts.contract.all_have_attribute(value, attribute_name)

Checks that all objects contained in value - be it a single object or an Iterable of objects - have the specified attribute.

Parameters:

• value – the value to check. It can be a single object, or an an Iterable of objects.
• attribute_name – a string containing the name of the attribute to look for.

Raises:

AttributeError if one of the objects does not contain the specified attribute.

contracts.contract.all_have_method(value, method_name)

Checks that all objects contained in value - be it a single object or an Iterable of objects - have the specified method.

Parameters:

• value – the value to check. It can be a single object, or an an Iterable of objects.
• method_name – a string containing the name of the method to look for.

Raises:

AttributeError if one of the objects does not contain the specified method.

contracts.contract.is_callable(value)

Checks that the specified value is a callable object (i.e. has a ‘__call__’ attribute).

Parameters:value – the value to check. Raises:TypeError if the value is not a callable object.

contracts.contract.is_equal(value, expected_value, expression_str=None)

Checks that the specified value is strictly equal to the expected value.

Parameters:

• value – the value to check.
• expected_value – the expected value.
• expression_str – (optional) a string representing the evaluated boolean expression (e.g. ‘len(a) == 1’).

Raises:

ValueError if the values are not strictly equal.

contracts.contract.is_equal_to_any(value, expected_values, expression_str=None)

Checks that the specified value is equal to at least one of the expected values.

Parameters:

• value – the value to check.
• expected_values – an Iterable object containing the expected values.
• expression_str – (optional) a string representing the evaluated boolean expression (e.g. ‘b > c’).

Raises:

ValueError if the value is not equal to any of the expected values.

contracts.contract.is_false(value, expression_str=None)

Checks that the specified value is equal to False.

Parameters:

• value – the value to check. It can be a standard variable’s value, or the result of an evaluated boolean expression (e.g. a or b > c).
• expression_str – (optional) a string representing the evaluated boolean expression (e.g. ‘b > c’).

Raises:

TypeError if the value is not False.

contracts.contract.is_greater_than(value, expected_value)

Checks that the specified value is greater than the expected value.

Parameters:

• value – the value to check.
• expected_value – the expected value.

Raises:

ValueError if the value is not greater than the expected value.

contracts.contract.is_greater_than_or_equal(value, expected_value)

Checks that the specified value is greater than or strictly equal to the expected value.

Parameters:

• value – the value to check.
• expected_value – the expected value.

Raises:

ValueError if the value is not greater than or strictly equal to the expected value.

contracts.contract.is_instance(value, cls)

Checks that the specified value is an instance of the given class.

Parameters:

• value – the value to check.
• cls – the expected class of the value.

Raises:

TypeError if the value is not an instance of the class.

contracts.contract.is_not_empty(value)

Checks that the specified value is not empty.

Parameters:value – the value to check. To be considered empty, it must be equal to None, or equal to “” if it’s a string. If it’s an Iterable object, its length must be equal to 0. Any other object type will never be considered empty. Raises:ValueError if the value is considered empty.

contracts.contract.is_not_none(value)

Checks that the specified value is not equal to None.

Parameters:value – the value to check. Raises:TypeError if the value is equal to None.

contracts.contract.is_true(value, expression_str=None)

Checks that the specified value is equal to True.

Parameters:

• value – the value to check. It can be a standard variable’s value, or the result of an evaluated boolean expression (e.g. a or b > c).
• expression_str – (optional) a string representing the evaluated boolean expression (e.g. ‘b > c’).

Raises:

TypeError if the value is not True.