Unlike many other programming languages out there, Python does not implicitly typecast integers (or floats) to strings when you concatenate them to strings.

You are watching: Typeerror: must be str, not int

Fortunately, Python has a handy built-in function str() which will convert the argument passed in to a string format.

The Wrong Way to Convert a String to an Integer in Python

Programmers coming from other programming languages may attempt to do the following string concatenation, which will produce an error:

age = 18string = "Hello, I am " + age + " years old"You can run this code on repl.it.

The error that shows up is:

Traceback (most recent call last): File "python", line 3, in TypeError: must be str, not intHere, TypeError: must be str, not int indicates that the integer must first be converted to a string before it can be concatenated.

The Correct Way to Convert a String to an Integer in Python

Here"s a simple concatenation example:

age = 18print("Hello, I am " + str(age) + " years old")# Output# Hello, I am 18 years oldYou can run this code on repl.it.

Here"s how to print 1 2 3 4 5 6 7 8 9 10 using a single string:

result = ""for i in range(1, 11): result += str(i) + " "print(result)# Output# 1 2 3 4 5 6 7 8 9 10You can run the code on repl.it.

Here"s a line-by-Line explanation of how the above code works:

First of all a variable ‘result’ is assigned to an empty string.The for loop is being used to iterate over a list of numbers.This list of numbers is generated using the range function.so range(1,11) is going to generate a list of numbers from 1 to 10.On each for loop iteration this ‘i’ variable is going to take up values from 1 to 10.On first iteration when the variable i=1,then the variable ,str(i) converts the ‘i’ which is an integer value to a string value.Since i=1, on the first iteration finally result=1.And the same process goes on until i=10 and finally after the last iteration result=1 2 3 4 5 6 7 8 9 10.Therefore when we finally print the result after the for loop the output on the console is ‘1 2 3 4 5 6 7 8 9 10’.

I hope you"ve found this helpful. Happy coding.

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Chris Tse

I'm a software engineer at Oracle Netsuite doing front end development with React and Sass. I also enjoy creating fast, responsive sites with the JAMStack.

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