The data type string has been introduced several times in previous chapters. In the chapter with titel “Expressions”, strings were quickly introduced. The brief discussion in that chapter ended with the statement that a string is a text, enclosed by either single or double quotes, which might be of any length, including zero characters long. The chapter also explained that you can concatenate two strings using the +, and that you can create a string that is the repetition of a shorter string by using a *. For example:

s1 = "apple"
s2 = 'banana'
print( s1 )
print( s2 )
print( s1 + s2 )
print( 3 * s1 )
print( s2 * 3 )
print( 2 * s1 + 2 * s2 )

In the chapter “Simple functions” I introduced the format() function to format strings. It also explained how you can get the length of a string using the len() function.

String comparisons were explained in the chapter “Conditions”. In particular the fact that the comparison operators compare strings using alphabetical rules, whereby capitals are always lower in the alphabet than lower case letters. This will be explained more in-depth in the present chapter. In the chapter “Conditions” I also explained how the in operator can be used to test the presence of characters or substrings in strings.

In the chapter with titel “Iterations” I explained how you can use a for loop to traverse all the characters in a string.

s1 = "orange"
s2 = "banana"
for letter in s1:
    if letter in s2:
        print( s1, "and", s2, "share the letter", letter )