4.2. Type Conversion

Sometimes it is necessary to convert values from one type to another. A common example occurs when a program receives string input, like "23", but needs to use the value as a number.

Python provides a few simple type conversion functions that allow us to change between data types. The functions int(), float() and str() will try to convert whatever is in the () (the argument) into the types int, float and string, respectively.

The int() function takes a floating point number or a string and turns it into whole number. Instead of rounding a decimal value, int() discards the decimal portion of the number.


Let’s see int() in action. Run the following code and note how int() changes the decimal values.

New vocabulary! Truncate: Remove the decimal part of a number WITHOUT rounding.

What happens if we try to convert a string to an integer, but the string is not actually a whole number? Add the following code to the editor above, then run the program again. You should see an error message.


In order for int() to work, the string has to be a whole number like '-2' or "526". Any string with letters, spaces, or punctuation will throw an error. Modify the new examples by deleting the days and ., then rerun the program. You should see the integers 80 and 1234.

The type converter float() turns an integer or an allowed string into a float. The type converter str() turns its argument into a string.

Remember that when we print a string, the quotes are removed. However, if we use the type() function, we can see the data type.


Let’s see float() and str() in action.

4.2.1. Check Your Understanding


What value is printed when the following statement runs?

print( int(53.785) )
  1. Nothing is printed. An error is generated.
  2. 53.785
  3. 54
  4. 53


Which of the following generates an error message when passed to float()? Feel free to try running each of the options.

  1. '3'
  2. 18
  3. '3 3'
  4. '12.38'