Why Can't I Add a String and a Number in Python?

You're writing one of your first Python programs. Maybe you're trying to display a player's score or a user's age. You write a line that seems perfectly logical:

print("Your score is: " + 95)

You hit run, expecting to see "Your score is: 95". But instead, your program crashes and you get this cryptic, angry-red message:

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

This single error is one of the most common and frustrating roadblocks for new Python developers. It feels like the computer is being difficult on purpose. Why can’t it just understand what you mean? This post will not only show you how to fix this error but, more importantly, explain the simple reason why it happens so you'll never be stuck on it again.

The Real Problem: Python's Two Meanings for "+"

The core of the problem is that the + symbol has two completely different jobs in Python, and it needs you to be clear about which job it should be doing.

1. For Numbers (Integers/Floats): The + symbol means mathematical addition.

   5 + 10 equals 15. This is the addition you learned in school.

2. For Text (Strings): The + symbol means concatenation (a fancy word for "joining together").

   "hello" + "world" equals "helloworld".

When you write "Your score is: " + 95, you are mixing these two worlds. You're giving Python a string and a number and telling it to use the + operator. Python freezes because it has a conflict: "Should I perform addition or concatenation? I can't do both at the same time."

To avoid making the wrong choice, Python simply stops and gives you the TypeError, telling you it only knows how to concatenate a string with another string, not with an integer.

The Solution: How to Combine Text and Numbers

To fix this, you need to be explicit. You have to tell Python to treat your number as a piece of text before you join it. Here are the two best ways to do it.

Solution 1: The str() Function (The Old Way)

You can manually convert your number into a string using the built-in str() function. This function takes a number (or any other data type) and returns its text representation.

The Broken Code:

Python

score = 95
print("Your score is: " + score) # This will cause the TypeError

The Fixed Code:

Python

score = 95
print("Your score is: " + str(score)) # Now it works!

By wrapping score in str(), you tell Python, "Hey, don't think of this as the number 95. Think of it as the text characters '9' and '5'." Now that both sides of the + are strings, Python knows its job is to concatenate, and the code runs perfectly.

Solution 2: F-Strings (The Modern, Better Way)

While str() works, there's a much cleaner and more powerful way to do this in modern Python: Formatted String Literals, or "f-strings" for short.

An f-string lets you embed variables directly inside a string. You just put the letter f before the opening quote and place your variables inside curly braces {}.

The F-String Solution:

Python

score = 95
print(f"Your score is: {score}") # This is the best way!

This code is cleaner, easier to read, and Python automatically handles the conversion for you behind the scenes. There's no need for str() or multiple + symbols. This is the method you should use in your projects.

Frequently Asked Questions (FAQs)

1. What does "concatenate" actually mean?

It's just a formal programming term for joining strings together, end-to-end.

2. Can I do the reverse? Can I convert a string into a number?

Yes! Python provides the int() and float() functions to do this. For example, int("100") will give you the number 100. This is crucial when you get input from a user, which is always read as a string.

3. Which method is better, str() concatenation or f-strings?

For combining text and variables, f-strings are almost always better. They are more efficient and make your code significantly easier to read, especially when you have multiple variables to include.

4. Does this TypeError happen with other operations?

No, this specific conflict is unique to the + operator because of its dual role. Operators like -, *, and / are only for numbers, so Python will give you a different TypeError if you try to use them with strings that aren't numbers.

Conclusion: You've Mastered a Core Concept

This TypeError isn't just a random error; it's Python's way of teaching you a fundamental rule about data types. By fixing it, you haven't just solved a bug—you've learned that you must be deliberate about how you combine different types of information.

You now understand that the + operator is context-sensitive and that you can use tools like str() and f-strings to control that context. This single piece of knowledge will save you countless hours of frustration on your coding journey.

What other Python error messages have you found confusing? Share them in the comments!