Posted on Nov 4, 2019 • Originally published at tech.serhatteker.com on Jul 20, 2019

Python Debug Decorators

Sometimes when debugging we like to print/log out all the inputs and outputs of a method: name, args, kwargs, dict etc.

We would have some IDE debug features for this purpose but sometimes we need manual debugging.

And while manual debugging I don't want to write logger.debug(<messsage>) to every one of two lines of a module.

The solution: Python Decorators

First configure a logger. For detail go to our post Python Logging Configuration. Then crate a module for our debugger decorators

#!/usr/bin/env python3 # -*- coding: utf-8 -*-  # utils/debuggers.py  class Debugger(object): """ Debug a method and return it back""" enabled = False def __init__(self, func): self.func = func def __call__(self, *args, **kwargs): if self.enabled: logger.debug(f'Entering : {self.func.__name__}') logger.debug(f'args, kwargs : {args, kwargs}') logger.debug(f'{self.func.__name__} returned : {self.func(*args, **kwargs)}') return self.func(*args, **kwargs)

Then call it and decorate your method like below:

#!/usr/bin/env python3 # -*- coding: utf-8 -*-  # main.py  from utils.debuggers import Debugger @Debugger def my_func(a, b, c, d): return a + b + c + d if __name__ == "__main__": Debugger.enabled = True args_dict = dict( a=1, b=2, c=5, d=-10 ) my_func(**args_dict)

Output will be like:

2019-07-21 18:43:25,635 [DEBUG] __main__: Entering : my_func 2019-07-21 18:43:25,635 [DEBUG] __main__: args, kwargs: ((), {'a': 1, 'b': 2, 'c': 5, 'd': -10}) 2019-07-21 18:43:25,635 [DEBUG] __main__: my_func returned -2

If you want a function instead of a class for debugging:

#!/usr/bin/env python3 # -*- coding: utf-8 -*-  # utils/decorators.py  import functools def debugmethod(func): """ Debug a method and return it back""" @functools.wraps(func) def wrapper(*args, **kwargs): return_value = func(*args, **kwargs) logger.debug(f'Calling : {func.__name__}') logger.debug(f'args, kwargs: {args, kwargs}') logger.debug(f'{func.__name__} returned {return_value}') return return_value return wrapper

Also if you like to know the execution time of the method;

#!/usr/bin/env python3 # -*- coding: utf-8 -*-  # utils/decorators.py  import time def timerun(func): """ Calculate the execution time of a method and return it back""" @functools.wraps(func) def wrapper(*args, **kwargs): start = time.time() result = func(*args, **kwargs) duration = time.time() - start logger.debug(f"Duration of {func.__name__} function was {duration}.") return result return wrapper

Output:

2019-07-21 18:43:25,636 [DEBUG] __main__: Duration of my_func was 0.00023937225341796875.

You can combine your decorators as below:

#!/usr/bin/env python3 # -*- coding: utf-8 -*-  # main.py  from utils.debuggers import debugmethod, timerun @timerun @debugmethod def my_func(a, b, c, d): return a + b + c + d if __name__ == "__main__": Debugger.enabled = True args_dict = dict( a=1, b=2, c=5, d=-10 ) my_func(**args_dict)

Output should be like this:

2019-07-21 18:43:25,635 [DEBUG] __main__: Calling : my_func 2019-07-21 18:43:25,635 [DEBUG] __main__: args, kwargs: ((), {'a': 1, 'b': 2, 'c': 5, 'd': -10}) 2019-07-21 18:43:25,635 [DEBUG] __main__: my_func returned -2 2019-07-21 18:43:25,636 [DEBUG] __main__: Duration of my_func was 0.00023937225341796875.

OK, all done.