Arcmap Field Calculator (Python): Add leading zeroes to single character values (1-9)

addzero.txt

Say I have a list of sections, out of the 36 numbers I want 1-9 to have the format 01,02, etc.
They are currently ints but my final field will be a text value so I need to convert the int to a text value to add a preceding 0.
Add a new field
use field calculator to fill the column based on the int, this will now be a text value.
Then run the following script in the field calculator:

Pre-Logic Script Code:
def addzero(f1, f2):
    if  len(f1) == 1:
        return "0" + f1
    else:
        return f1

Field =:
addzero( !FIELD1!, !FIELD2!)