Create a decorator in Python, which remembers last output of the function

Question

I need to create a decorator which remembers last call result of the function which it decorates. For example, I have a function:

def summarize(*args):
    result = ""
    for i in args:
        result += i
    print('New result = ', result)
    return result

And I need to use decorator (without any classes or smth), to make it like that:

summarize("he", "llo")
>>> "Previous result = 'None'"
>>> "New result = 'hello'"
summarize("good", "bye")
>>> "Previous result = 'hello'"
>>> "New result = 'goodbye'"

I’m new to decorators and now I don’t have any idea how to make it like that. I get needed result only when I try to call the function twice in one run.

Asked By: stupid_beaver

||

Source

Answer 1

See below :

def historic_results(func):
    # retrive historic outputs from hitoric_outputs.txt file if it exists
    with open('historic_outputs.txt', "r") as f:
        try:
           previous_outputs = f.readlines()
        except:
           previous_outputs = []

    def inner(*args, **kwargs):
        
        if not previous_outputs : print("Previous Result:", None)
        if previous_outputs: 
            for item in previous_outputs: print("Previous Result:", item)

        # append the output in the historic outputs txt file
        with open('historic_outputs.txt', 'a') as f:
            f.write(func(*args, **kwargs) + "n")
        
        print("New Result", func(*args, **kwargs))

        return func(*args, **kwargs)

    return inner


@historic_results
def summarize(*args):
    result = ""
    for i in args:
        result += i
    return result

Test :

summarize("hel", "lo")
summarize("Ami", "ne")
summarize("stupid", "_beaver")

Output:

Previous Result: None
New Result hello

Previous Result: hello
New Result Amine

Previous Result: hello
Previous Result: Amine
New Result stupid_beaver

Answered By: AmineBTG

Answer 2

prev_result = None

def remember_result(func):

    def wrapper(*args):
        global prev_result
        print(f"Prev result = '{prev_result}'")
        prev_result = func(*args)
    return wrapper

@remember_result
def summarize(*args):
    result = ""
    for i in args:
        result += i
    print('New result = ', result)
    return result

Answered By: Yurij Halibey

Create a decorator in Python, which remembers last output of the function

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