Making a calculator in python

Question

So i Tried using this chunk of code to create a calculator in python, since I have just started learning. Thing is, it always says I enter an invalid option, passing through all my if-else statements, even when I do enter a valid option. What did I do wrong ?

    #!/usr/bin/env python

def add():
    return float(input ("Enter a number: ")) + float(input ("Enter another number: "))

def subt():
    return float(input ("Enter a number: ")) - float(input ("Enter another number: "))

def mult():
    return float(input ("Enter a number: ")) * float(input ("Enter another number: "))

def power():
    return float(input ("Enter a number: ")) ** float(input ("Enter another number: "))

def division():
    return float (input ("Enter a number: ")) / float (input ("Enter another number: "))

s = input("Add, Subtract, Multiply, Divide or Power two Numbers: ")
if s == "add":
    print(add ())
elif s == "subtract":
    print(subt ())
elif s == "multiply":
    print(mult ())
elif s == "power":
    print(power ())
elif s == "division":
    print(division ())
else:
    print ("Enter a valid option")

Answer 1

If sounds like you're using Python2. In that case, use raw_input instead of input, otherwise it tries to locate a variable/function by the users string input and place the object-name in s. Where as raw_input takes a user input as a string and places the string s.

This is the short answer of the difference between the two.

#!/usr/bin/env python

def add():
    return float(input ("Enter a number: ")) + float(input ("Enter another number: "))

def subt():
    return float(input ("Enter a number: ")) - float(input ("Enter another number: "))

def mult():
    return float(input ("Enter a number: ")) * float(input ("Enter another number: "))

def power():
    return float(input ("Enter a number: ")) ** float(input ("Enter another number: "))

def division():
    return float (input ("Enter a number: ")) / float (input ("Enter another number: "))

s = raw_input("Add, Subtract, Multiply, Divide or Power two Numbers: ")
if s == "add":
    print(add())
elif s == "subtract":
    print(subt())
elif s == "multiply":
    print(mult())
elif s == "power":
    print(power())
elif s == "division":
    print(division())
else:
    print("Enter a valid option")

There's a lot of differences in Python2 and Python3, specifying which one you're using helps a lot. It either says it at the top of your terminal when you enter the python interpreter or if you execute python --version.