The code below is an example that shows that we can do design by contract in python without any non-standard module.
Python, 30 lines
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def function(a, b): # description and test """Adds an integer and a float and returns a str. >>> function(1, 3.0) '4.0' """ # precondition assert isinstance(a, int), 'a argument should be int' assert isinstance(b, float), 'b argument should be float' #implementation try: c = str(a + b) return c # postcondition finally: assert isinstance(c, str), 'c variable should be str' # run all docstring test on debug mode if __debug__: import doctest doctest.testmod() if __name__ == '__main__': # do something pass
This pattern can be used in function definitions, class definitions, modules and in the same places where you can use documentation strings, try/finally statement and assert statement.
Tags: demo, design_pattern, productivity
Note that this code is not a good example of using assertions. I recommend reading the tutorial When to use assert made by Steven D'Aprano.
Did you read the tutorial that you referenced? "assertions should be used for: [...] * checking contracts (e.g. pre-conditions and post-conditions);" I would say that this is a good example of using assertions.