Help needed in Using Python Functions

Question

I am getting an error on line "print(operation(a, b))" as TypeError: 'str' object is not callable even when the input is either multiply or minus, however if i comment the above code and un-comment the commented code i get the desired results: 28 and -3

def multiply(x, y):
return x * y

def minus(x, y):
return x - y

a = 4
b = 7
operation = input()
print (operation)
print(operation(a, b))

#operation = multiply
#print(operation(a, b))
#operation = minus
#print(operation(a, b))

Answer 1

input() returns a string and you can't call a string. In your positive example you are assigning multiply, which is a function, to operation variable. And so, operation becomes a function, too, not a string.

Answer 2

You could try using eval(), like this:

operation = input()
print(eval(operation+'((a, b))'))

>>>
multiply
28

Answer 3

I think that is because you can't call function as user input.

Answer 4

@Nirjhar Kuba's change does what you are looking for.
@Kuba Thank you for teaching me a cool trick.

Answer 5

In first case your variable operation is string. In the section that works fine your variable is function. You can try to use built-in function type(operation) in both cases and you will understand. eval() function basically transforms string into executable code.

Answer 6

Thanks Kuba.... the eval function did the desired work:
operation = input()
print(eval(operation+'(a, b)'))

however my question still persist that why does the same Print functioncall gives error and taking input from user?

#This code gives error
operation = input()
print (operation) #user input is multiply
print(operation(a, b)) #giver error

#This code works fine
operation = multiply
print(operation(a, b))

may be i am missing out some concept.

Answer 7

Thanks @Milos