The error message:
TypeError: can only concatenate str (not "int") to str
occurs when you try to combine a string (str) with an integer (int) using the + operator.
1. Causes and Solutions
Cause 1: Trying to Concatenate a String and an Integer
Python does not allow direct concatenation of a string and an integer.
Incorrect Code:
age = 25
message = "I am " + age + " years old" # Error: Cannot concatenate str and int
Error Output:
TypeError: can only concatenate str (not "int") to str
Solution: Convert int to str Before Concatenation
message = "I am " + str(age) + " years old"
print(message) # Output: I am 25 years old
Cause 2: Using + Instead of , in print()
If you’re printing multiple values, use commas (,) instead of + to avoid type issues.
Incorrect Code:
age = 30
print("My age is " + age) # TypeError
Solution: Use a Comma (,) in print()
print("My age is", age) # Works fine
# Output: My age is 30
Cause 3: Concatenating a Number Inside a Loop
When looping, if you append a number to a string incorrectly, a TypeError will occur.
Incorrect Code:
total = "Total: "
num = 100
total += num # Error: Trying to add int to str
Solution: Convert the Integer to a String
total += str(num)
print(total) # Output: Total: 100
Cause 4: Using join() with Non-String Elements
The join() method works only with strings, so if you try to join a list containing numbers, you’ll get a TypeError.
Incorrect Code:
numbers = [1, 2, 3]
result = "-".join(numbers) # TypeError: int in list
Solution: Convert All Elements to Strings
result = "-".join(map(str, numbers))
print(result) # Output: 1-2-3