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TypeError: can only concatenate str (not "int") to str

What it means

You used + to join a string with something that is not a string, here a whole number. Python does not turn numbers into text on its own, because "5" + 3 could mean "53" or 8. Convert the number first, or use an f-string.

1. Joining text and a number with `+`

This raises the error

Broken
age = 25
print("I am " + age + " years old")
Output
Traceback (most recent call last):
  File "<exec>", line 2, in <module>
TypeError: can only concatenate str (not "int") to str

The fix

Fixed
age = 25
print(f"I am {age} years old")
Output
I am 25 years old

An f-string puts the value into the text for you. "I am " + str(age) + " years old" works too.

Try fixing it yourself in the editor

2. A calculated amount added to text

This raises the error

Broken
price = 4.5
quantity = 3
print("Total: " + price * quantity)
Output
Traceback (most recent call last):
  File "<exec>", line 3, in <module>
TypeError: can only concatenate str (not "float") to str

The fix

Fixed
price = 4.5
quantity = 3
print(f"Total: {price * quantity:.2f}")
Output
Total: 13.50

The result of price * quantity is a float, so the message says not "float". The f-string turns it into text, and :.2f shows two decimal places.

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3. Building a string from numbers in a loop

This raises the error

Broken
digits = [3, 1, 4]
code = ""
for d in digits:
code = code + d
print(code)
Output
Traceback (most recent call last):
  File "<exec>", line 4, in <module>
TypeError: can only concatenate str (not "int") to str

The fix

Fixed
digits = [3, 1, 4]
code = ""
for d in digits:
code = code + str(d)
print(code)
Output
314

Each number must become text before it can join the string. "".join(str(d) for d in digits) does the same in one line.

Try fixing it yourself in the editor

When you see this error, check

  • Wrap numbers in str() before joining them to text with +.
  • Prefer f-strings, like f"Score: {score}".
  • print() accepts several values separated by commas and converts them itself: print("Age:", age).
  • If you meant to add numbers, convert the text instead: int("5") + 3.

Related errors

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