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TypeError: unsupported operand type(s) for +: 'int' and 'str'

What it means

You used an operator such as +, -, * or / on two values that cannot be combined that way. The message names the operator and the two types in order: here a number on the left and a string on the right.

1. A number stored as text

This raises the error

Broken
price = 10
tax = "2" # the quotes make this text
print(price + tax)
Output
Traceback (most recent call last):
  File "<exec>", line 3, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'str'

The fix

Fixed
price = 10
tax = "2"
print(price + int(tax))
Output
12

int() turns the text "2" into the number 2. Values read from files, forms and input() are text until you convert them.

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2. Adding up a list of strings with `sum()`

This raises the error

Broken
line = "4 8 15 16"
numbers = line.split()
print(sum(numbers))
Output
Traceback (most recent call last):
  File "<exec>", line 3, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'str'

The fix

Fixed
line = "4 8 15 16"
numbers = [int(n) for n in line.split()]
print(sum(numbers))
Output
43

split() gives a list of strings. sum() starts from 0 and adds each item, so every item must be a number first.

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3. A function that prints instead of returning

This raises the error

Broken
def add(a, b):
print(a + b)
total = add(2, 3) + 10
print(total)
Output
5
Traceback (most recent call last):
  File "<exec>", line 4, in <module>
TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'

The fix

Fixed
def add(a, b):
return a + b
total = add(2, 3) + 10
print(total)
Output
15

print() only shows a value. return hands it back to the caller. Without return the function gives None, and the message says 'NoneType' and 'int'.

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When you see this error, check

  • Read the two types in the message: they tell you which side to convert.
  • Convert text to numbers with int() or float() before doing math.
  • Print type(x) for each value on the failing line.
  • If one of the types is NoneType, a function is missing its return.

Related errors

All Python errors · How to read a traceback · Step through your code