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

You're writing a Python script to generate a summary message. You have a user's name (text) and their score (a number), and you want to combine them into a friendly sentence:

Python

user_name = "Alice"
user_score = 150

# Attempt to combine them
message = "Hello, " + user_name + "! Your score is: " + user_score + " points."

print(message)

You run the code, expecting Hello, Alice! Your score is: 150 points., but instead, your program crashes with a TypeError:

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

This error message is a classic head-scratcher for beginners. Why can't Python just combine a number and text? It seems so obvious to a human. This isn't Python being difficult; it's Python being precise about data types, a fundamental concept we touched on in What Happens When You Ask an AI to Add "Popsicles" + 3?.

The Problem: Adding Apples and Oranges

Python is a strongly-typed language. This means it cares deeply about the "type" of data you are working with (e.g., is it a string (text), an int (whole number), a float (decimal number), etc.?).

The + operator has different meanings depending on the data types:

• For numbers (int, float): + means mathematical addition.

  5 + 10 equals 15.

• For strings (str): + means concatenation (joining strings end-to-end).

  "Hello" + "World" equals "HelloWorld".

When you try to combine a string with an int using +, Python doesn't know which operation you intend. Do you want to try to add the number to the string (which makes no sense mathematically)? Or do you want to join them as text (which requires the number to become text first)? Because it can't guess, it throws a TypeError to prevent an ambiguous operation from producing unexpected results.

The error can only concatenate str (not "int") to str is Python's way of saying, "Hey, I was trying to join strings together, but you gave me an integer. I can only join strings with other strings!"

The Solution: Convert Numbers to Strings

To fix this, you need to explicitly convert the number into a string before trying to combine it with other strings. Python provides the str() function for exactly this purpose.

Method 1: Using str() for Concatenation

Convert any non-string items to strings before using + for joining.

Python

user_name = "Alice"
user_score = 150

# Convert user_score to a string using str()
message = "Hello, " + user_name + "! Your score is: " + str(user_score) + " points."

print(message)
# Output: Hello, Alice! Your score is: 150 points.

This works perfectly because now all parts being "added" with + are strings.

Method 2: Using f-strings (The Modern Pythonic Way)

While str() works, the most modern, readable, and often preferred way to embed variables (of any type) into strings is using f-strings (formatted string literals). They make your code much cleaner.

An f-string starts with an f before the opening quote. You can then put any Python expression (including variables) directly inside curly braces {} within the string. Python automatically converts them to their string representation.

Python

user_name = "Alice"
user_score = 150

# Using an f-string
message = f"Hello, {user_name}! Your score is: {user_score} points."

print(message)
# Output: Hello, Alice! Your score is: 150 points.

This is by far the cleanest and most recommended method for string formatting in Python 3.6 and above.

Method 3: Using .format() (Still Common, Less Concise)

The .format() method is an older (but still widely used) way to achieve the same result.

Python

user_name = "Alice"
user_score = 150

# Using .format()
message = "Hello, {}! Your score is: {} points.".format(user_name, user_score)

print(message)
# Output: Hello, Alice! Your score is: 150 points.

Frequently Asked Questions (FAQs)

1. Can I convert a string to a number?

Yes, if the string actually represents a number. Use int() for whole numbers and float() for decimal numbers.

age_str = "30"

age_int = int(age_str)

2. What if my string isn't a valid number (e.g., "hello")?

Trying to convert "hello" to an int will cause a ValueError. You'll need to use try-except blocks to handle such cases gracefully, which we'll cover in a future post!

3. When should I use + for strings versus f-strings?

For simple joining of two or three literal strings, + is fine. For embedding variables or expressions into a sentence, f-strings are almost always the best choice due to their readability and flexibility.

Conclusion: Type Precision for Clearer Code

The TypeError when concatenating strings and numbers is a powerful lesson in Python's precision. It forces you to be explicit about your intentions, preventing potential bugs down the line. By using str() for explicit conversion or, even better, embracing the simplicity of f-strings, you can seamlessly combine different data types into clear, human-readable messages.

You've learned to speak Python's language more fluently, leading to cleaner code and fewer unexpected errors.