Answer 1

A callback is a function. In Python, functions are objects, so the name of a function can be used as a variable to another function.

def add():
...

anotherfunction(add)

Functions which accept a callback(function) as an argument usually require the arguments which callback accept.

def add(a, b):
return a+b

def main(a, b, _callback=None):
print("adding {} + {}".format(a, b))
if _callback:
print("Result : ", _callback(a , b))

main(1, 2, add)

Here, I am passing add to function main. Main is called the call back function.