Function as objects in python. Help

Question

Recently i learnt that i can assign a variable the name of the funcion like this:
def hello(x):.....
greeting = hello
print(greeting(a))
and it works... but when i try to give the function the user input it doesn't work.
def subtract(x, y):.....
def add(x,y):....
operation = input("Which operation do you want to do?")
print(operation(3, 4))
How should i fix that? I'd like to rebuild a better version of simple calculator where you can choose the operation and this string becomes the name of the function that you want to call.

Answer 1

You have to distinguish between function object and function call.

If you write

x=f

you store the function. If instead you write

x=f()

you CALL the function and store what it returns (or None).

For example you can store function objects in a dict and call it from there:

d = {'function 1': f1, 'function 2': f2}

And then call it by accessing the dict.

d['function 1']()

for example calls f1.

So since you get user input as string, you can directly call it using the input.

inp=input() # say user writes 'function 1'
d[inp]()