How to parse user input as a number

Question

I am making a calculator program in my Python, following a tutorial. Here is my code:

print ("This is a calculator program, press Enter to continue")
a = input()
while a == "":
 print("Enter 1 for option 1 which adds")
 print("Enter 2 for option 2 which subtracts")
 print("Enter 3 for option 3 which multiply")
 print("Enter 4 for option 4 which divides")
 print("Enter 5 for option 5 which quits",)
 Option = input("Enter an option number:")
 int(Option)
 if Option == 1:
 Number1 = input("Enter number 1")
 Number2 = input("Enter number 2")
 int(Number1,Number2)
 print(Result = Number1 + Number2)
 if Option == 2:
 Number1 = input("Enter number 1")
 Number2 = input("Enter number 2")
 int(Number1,Number2)
 print(Result = Number1 - Number2)
 if Option == 3:
 Number1 = input("Enter number 1")
 Number2 = input("Enter number 2")
 int(Number1,Number2)
 print(Result = Number1 * Number2)
 if Option == 4:
 Number1 = input("Enter number 1")
 Number2 = input("Enter number 2")
 int(Number1,Number2)
 print(Result = Number1 / Number2)
 if Option == 5:
 break

It is very basic, it gets up to the point of printing all the option numbers and then asks me to pick one. So I enter "1" as a string, parsing it to an integer 1. However it doesn't go straight to option 1 and instead loops again which is fine I will sort that out later. But again it doesn't go to any option when I enter 1-5. I think I typed in the wrong code to parse it or something?

• agconti: your not saving out the int function. try you_var =int(Number1,Number2)
• Gabi Purcaru: a = input() should be inside the while loop, and also instead of print(Result = Number1 + Number2) you should print(Number1 + Number2) (similarly for the other options)
• Martijn Pieters: You should really use a better title. Almost every beginner in Python just started learning, but that doesn't mean that your question would be useful to them.
• Gabi Purcaru: also Number1 = int(input(...))
• Paulo Bu: I think your main problem is the comparison Option = 1. Option will be a str and 1 is an int. It'll always return false.

Answer 1

input() converts the input to a string, so if you need to read an int, you have to cast it.

In the if condition, you could cast the input() result (a string) to int:

Number1 = int(input("Enter number 1"))

then create a variable, let's say result and assign it the sum of the numbers:

result = Number1 + Number2

and finally print the result

print "Result = " + str(result)

The final code should look like this:

print ("This is a calculator program, press Enter to continue")
a = input()
while a == "":
 print
 print("Enter 1 for option 1 which adds")
 print("Enter 2 for option 2 which subtracts")
 print("Enter 3 for option 3 which multiply")
 print("Enter 4 for option 4 which divides")
 print("Enter 5 for option 5 which quits",)
 Option = input("Enter an option number:")
 if Option == 1:
 Number1 = int(input("Enter number 1"))
 Number2 = int(input("Enter number 2"))
 result = Number1 + Number2
 print "Result = " + str(result) # To print you have to cast to `str`
 elif Option == 2:
 ...
 elif Option == 3:
 ...
 elif Option == 4:
 ...
 else:
 break

Notes:

• You could use an if-elif-else as the structure, so if Option == 1, the following conditions won't be checked.

• I would also recommend you to follow Python naming convention. Your variable Number1 should be called number1 and so on.

• senshin: There is no raw_input in Python 3, which OP seems to be using. Python 3 input behaves like Python 2 raw_input, and there is no Python 3 equivalent of Python 2's input.

Answer 2

Result of input function is a string, you need to convert it to int, using int type .

>>> foo = "3"
>>> foo
'3'
>>> int(foo)
3

Your misconception might come from that python is a dynamically typed language. But remember that despite variables themselves are untyped, variable values have types.

>>> type(foo)
<class 'str'>
>>> type(int(foo))
<class 'int'>

Answer 3

Your code should look more like this:

print("This is a calculator program. Press Enter to continue.")
while True:
 _ = input()
 print("Enter 1 for option 1 which adds")
 print("Enter 2 for option 2 which subtracts")
 print("Enter 3 for option 3 which multiply")
 print("Enter 4 for option 4 which divides")
 print("Enter 5 for option 5 which quits")
 option = int(input("Enter an option number: "))
 if option == 5:
 break
 else:
 number1 = int(input("Enter number 1: "))
 number2 = int(input("Enter number 2: "))
 if option == 1:
 result = number1 + number2
 elif option == 2:
 result = number1 - number2
 elif option == 3:
 result = number1 * number2
 elif option == 4:
 result = number1 / number2
 print(result)

Salient points:

• You aren't doing anything with a. So I got rid of it, and put a call to input that stores its result in _, which is the standard name for a variable whose value you don't care about.
• You must explicitly convert option to an int. Python will not implicitly convert for you, and so '1' != 1.
• You cannot convert to an int in-place - writing int(number1) does nothing. You must write number1 = int(number1) or similar.
• You cannot convert multiple strings to an int in a single statement of the form int(number1, number2). What you're actually doing here is calling int(x, base), where you convert x into an int, interpreted as being in base base.
• I refactored your if statements to be more concise
• Variable names are typically lowercase in Python.
• You cannot assign to a variable inside a print statement.

• Foysal94: Hey do you know where you said Option = int(input("Enter an option number:")), is it possible to do it like this Option = input("Enter an option number") /newline int(Option)? I forgot to put that in my orignal post, the one line of code.

Answer 4

that code posted contains several errors, below is the corrected code:

print ("This is a calculator program, press Enter to continue")
a = input()
while a == "":
 print("Enter 1 for option 1 which adds")
 print("Enter 2 for option 2 which subtracts")
 print("Enter 3 for option 3 which multiply")
 print("Enter 4 for option 4 which divides")
 print("Enter 5 for option 5 which quits",)
 Option = int(input("Enter an option number:"))
 if Option == 1:
 Number1 = int(input("Enter number 1"))
 Number2 = int(input("Enter number 2"))
 # int(Number1,Number2)
 Result = Number1 + Number2
 if Option == 2:
 Number1 = int(input("Enter number 1"))
 Number2 = int(input("Enter number 2"))
 # int(Number1,Number2)
 Result = Number1 - Number2
 if Option == 3:
 Number1 = int(input("Enter number 1"))
 Number2 = int(input("Enter number 2"))
 # int(Number1,Number2)
 Result = Number1 * Number2
 if Option == 4:
 Number1 = int(input("Enter number 1"))
 Number2 = int(input("Enter number 2"))
 # int(Number1,Number2)
 Result = Number1 / Number2
 print(Result)
 if Option == 5:
 break

• Foysal94: Hey do you know where you said Option = int(input("Enter an option number:")), is it possible to do it like this Option = input("Enter an option number") /newline int(Option)?
• zhangxaochen: @user3216729, yes but you need to do Option=int(Option)
• Foysal94: ah right ty, I come from C# so thats why I would do it like that. I tend to go for 1 or 2 more lines instead of doing all in one line for me personally, jsut helps me look over it.Thanks!
• zhangxaochen: @user3216729, you could upvote or accept it if you like this answer. ;)
• Foysal94: C# is the only language I know so far, and in C# I would do it this way Console.Write("Enter an option number") /newline string option = Console.ReadLine() /newline optionnumber = int.Parse(option). Is an input() just the same as a Console.Write()/Console.WriteLine()? It doesnt let me upvote :/

Answer 5

I corrected your code.

_ = input("This is a calculator program, press Enter to continue")
print ("""Enter 1 for option 1 which adds
 Enter 2 for option 2 which subtracts
 Enter 3 for option 3 which multiplies
 Enter 4 for option 4 which divides
 Enter 5 for option 5 which quits""")
while True:
 Option = input("Enter an option number: ")
 if Option == '1':
 Number1 = int(input("Enter number 1: "))
 Number2 = int(input("Enter number 2: "))
 print("The Result is {0}".format(Number1 + Number2))
 elif Option == '2':
 Number1 = int(input("Enter number 1: "))
 Number2 = int(input("Enter number 2: "))
 print("The Result is {0}".format(Number1 - Number2))
 elif Option == '3':
 Number1 = int(input("Enter number 1: "))
 Number2 = int(input("Enter number 2: "))
 print("The Result is {0}".format(Number1 * Number2))
 elif Option == '4':
 Number1 = int(input("Enter number 1: "))
 Number2 = int(input("Enter number 2: "))
 print("The Result is {0}".format(Number1 / Number2))
 else:
 break

Notes:

1. Triple quote syntax is good for long multiline strings.
2. The pythonic way of formatting a printed string is the str.format method.

Good luck learning!