Simple Python Calculator

Question

Hi I am new to python and I am practicing by making a simple calculator. The program lets me input numerical values for meal, tax, and tip but when doing the calculation I get this error:

Traceback (most recent call last):
 File "C:/Users/chacha04231991/Desktop/pytuts/mealcost.py", line 5, in <module>
 meal = meal + meal * tax
TypeError: can't multiply sequence by non-int of type 'str'

The is the code:

meal = raw_input('Enter meal cost: ')
tax = raw_input('Enter tax price in decimal #: ')
tip = raw_input('Enter tip amount in decimal #: ')
meal = meal + meal * tax
meal = meal + meal * tip
total = meal
print 'your meal total is ', total

• alexvassel: result of the raw_input is str.

Answer 1

You need to convert your inputs from strings to numbers, e.g. integers:

meal = int(raw_input('Enter meal cost: '))
tax = int(raw_input('Enter tax price in decimal #: '))
tip = int(raw_input('Enter tip amount in decimal #: '))

You could also use the decimal type if you need to enter fractional monetary amounts.

from decimal import Decimal 
meal = Decimal(raw_input('Enter meal cost: '))
tax = Decimal(raw_input('Enter tax price in decimal #: '))
tip = Decimal(raw_input('Enter tip amount in decimal #: '))

I would advise you not to use floats for this because it will give rounding errors.

• codeYah: It works fine using float but when I try decimal is gives this error: Traceback (most recent call last): File "C:/Users/chacha04231991/Desktop/pytuts/mealcost.py", line 4, in <module> tax = decimal(raw_input('Enter tax price in decimal #: ')) NameError: name 'decimal' is not defined
• Mark Byers: @codeYah: decimal with a small d is the name of the module. The type Decimal has a capital D.

Answer 2

when you use raw_input, the input you get is of type str

>>> meal = raw_input('Enter meal cost: ')
Enter meal cost: 5
>>> type(meal)
<type 'str'>

you should convert it to int/float before performing action

>>> meal = int(raw_input('Enter meal cost: '))
Enter meal cost: 5
>>> type(meal)
<type 'int'>

Answer 3

Input is a string by default in python. You will have to convert it to an integer before multiplying.

int(meal)
int(tax)
int(tip)

should do the trick.

Parse String to Float or Int

Answer 4

This is simple and also I wrote this code depending on the user operand input as string..

def calculator(a, b, operand):
 result = 0
 if operand is '+':
 result = a + b
 elif operand is '-':
 result = a - b
 elif operand is '*':
 result = a * b
 elif operand is '/':
 result = a / b
 return result
calculator(2, 3, '+')
output -> 5

Answer 5

By default, python assumes all input as string value. So we need to convert string values to numbers through either float or int.

• Eric Aya: This has already been mentioned in the other answers.