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Python - Passing a function into another function

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How do you pass a function to another function in Python?

A function name can become a variable name (and thus be passed as an argument) by dropping the parentheses. A variable name can become a function name by adding the parentheses. In your example, equate the variable rules to one of your functions, leaving off the parentheses and the mention of the argument.

Can you pass a function to another function?

Functions can be passed into other functions Functions, like any other object, can be passed as an argument to another function.

How do you pass a function call as an argument in Python?

To pass a function as an argument to another function, write the name of the function without parenthesis in the function call statement (just like what we do with variables) and accept the reference of the function as a parameter in the called function.

Can you call a function in another function Python?

In Python, any written function can be called by another function. Note that this could be the most elegant way of breaking a problem into chunks of small problems.


Just pass it in like any other parameter:

def a(x):
    return "a(%s)" % (x,)

def b(f,x):
    return f(x)

print b(a,10)

Treat function as variable in your program so you can just pass them to other functions easily:

def test ():
   print "test was invoked"

def invoker(func):
   func()

invoker(test)  # prints test was invoked

For passing both a function, and any arguments to the function:

from typing import Callable    

def looper(fn: Callable, n:int, *args, **kwargs):
    """
    Call a function `n` times

    Parameters
    ----------
    fn: Callable
        Function to be called.
    n: int
        Number of times to call `func`.
    *args
        Positional arguments to be passed to `func`.
    **kwargs
        Keyword arguments to be passed to `func`.

    Example
    -------
    >>> def foo(a:Union[float, int], b:Union[float, int]):
    ...    '''The function to pass'''
    ...    print(a+b)
    >>> looper(foo, 3, 2, b=4)
    6
    6
    6       
    """
    for i in range(n):
        fn(*args, **kwargs)

Depending on what you are doing, it could make sense to define a decorator, or perhaps use functools.partial.


Just pass it in, like this:

Game(list_a, list_b, Rule1)

and then your Game function could look something like this (still pseudocode):

def Game(listA, listB, rules=None):
    if rules:
        # do something useful
        # ...
        result = rules(variable) # this is how you can call your rule
    else:
        # do something useful without rules

A function name can become a variable name (and thus be passed as an argument) by dropping the parentheses. A variable name can become a function name by adding the parentheses.

In your example, equate the variable rules to one of your functions, leaving off the parentheses and the mention of the argument. Then in your game() function, invoke rules( v ) with the parentheses and the v parameter.

if puzzle == type1:
    rules = Rule1
else:
    rules = Rule2

def Game(listA, listB, rules):
    if rules( v ) == True:
        do...
    else:
        do...