How to change an output?-CodePudding

So my task is: Write a decorator that logs information about calls of decorated functions, the values of its arguments, keyword arguments, and execution time. The log should be written to a file.

My solution is:

``
from time import time

def log(func):
    def wrapper(*args, **kwargs):
        start_time = time()
        func(*args, **kwargs)
        end_time = time() - start_time
        with open('log.txt', 'a ') as file:
            file.write(f'{func.__name__}; args: {args}, kwargs: {kwargs}, execution time: {end_time}\n sec.')
    return wrapper
``

I have to test it with a function:

``
@log
def foo(a, b, c):
    ...

foo(1, 2, c=3)
``

And expected outcome in log.txt file must look something like this:

...
foo; args: a=1, b=2; kwargs: c=3; execution time: 0.12 sec.
...

But what I get is:

some_fun; args: (1, 2), kwargs: {'c': 3}, execution time: 0.0
sec.

How should I change my code to get an expected outcome?

CodePudding user response：

You could use signature from the inspect module (standard library) to fetch the variable names, and then use some string manipulations to get the desired output:

from inspect import signature
from time import perf_counter

def log(func):
    params = signature(func).parameters.keys()
    logmsg = func.__name__   "; args: {}; kwargs: {}; execution time: {} sec.\n"
    def wrapper(*args, **kwargs):
        start_time = perf_counter()
        func(*args, **kwargs)
        extime = perf_counter() - start_time
        with open("log.txt", "a ") as file:
            args = ", ".join(f"{name}={value}" for name, value in zip(params, args))
            kwargs = ", ".join(f"{name}={value}" for name, value in kwargs.items())
            file.write(logmsg.format(args, kwargs, extime))
    return wrapper

perf_counter is better for performance measurement.

(In case you're not aware: Your wrapper builds a function that only returns None. If func returns something that the wrapped func should also return, then use result = func(*args, **kwargs) and do return result at the end.)

As pointed out by @zvone: This doesn't capture default arguments. If that is a concern, then you could use the following adjustment (which makes it a bit more complicated):

from inspect import signature
from time import perf_counter

def log(func):
    sig = signature(func)
    logmsg = func.__name__   "; args: {}; kwargs: {}; execution time: {} sec.\n"
    def wrapper(*args, **kwargs):
        start_time = perf_counter()
        func(*args, **kwargs)
        extime = perf_counter() - start_time
        with open("log.txt", "a ") as file:
            binds = sig.bind(*args, **kwargs)
            binds.apply_defaults()
            pairs = list(binds.arguments.items())
            args_str = ", ".join(f"{n}={v}" for n, v in pairs[:len(args)])
            kwargs_str = ", ".join(f"{n}={v}" for n, v in pairs[len(args):])
            file.write(logmsg.format(args_str, kwargs_str, extime))
    return wrapper

Here the default arguments that aren't given in args or kwargs get added to kwargs with their default value (only for the purpose of logging).

CodePudding user response：

For now i think it's not possible, because what are you doing is displaying full {kwargs} and {args}, and they will only return a list.

Solution for this is, that you will write a for loop and display each item from {args} and {kwargs}, and for time, you shoul use another function not

start_time = time();

find other function in the python docs: https://docs.python.org/3/library/time.html#module-time