How can Interceptor in python be applied

Question

I need to know when a function is called and do something after calling the function. It seems Interceptor can do it.

How can I use Interceptor in python ?

Answer 1

This can be done using decorators:

from functools import wraps


def iterceptor(func):
    print('this is executed at function definition time (def my_func)')

    @wraps(func)
    def wrapper(*args, **kwargs):
        print('this is executed before function call')
        result = func(*args, **kwargs)
        print('this is executed after function call')
        return result

    return wrapper


@iterceptor
def my_func(n):
    print('this is my_func')
    print('n =', n)


my_func(4)

Output:

this is executed at function definition time (def my_func)
this is executed before function call
this is my_func
n = 4
this is executed after function call

@iterceptor replaces my_func with the result of execution of the iterceptor function, that is with wrapper function. wrapper wraps the given function in some code, usually preserving the arguments and execution result of wrappee, but adds some additional behavior.

@wraps(func) is there to copy the signature/docstring data of the function func onto the newly created wrapper function.

More info:

• http://python-3-patterns-idioms-test.readthedocs.io/en/latest/PythonDecorators.html
• https://www.python.org/dev/peps/pep-0318/