String Methods

From an existing string, related strings can be constructed using string methods, which are functions that operate on strings. These methods are called by placing a dot after the string, then calling the function.

For example, the following method generates an uppercased version of a string.

"loud".upper()

'LOUD'

Perhaps the most important method is replace, which replaces all instances of a substring within the string. The replace method takes two arguments, the text to be replaced and its replacement.

'hitchhiker'.replace('hi', 'ma')

'matchmaker'

String methods can also be invoked using variable names, as long as those names are bound to strings. So, for instance, the following two-step process generates the word “degrade” starting from “train” by first creating “ingrain” and then applying a second replacement.

s = "train"
t = s.replace('t', 'ing')
u = t.replace('in', 'de')
u

'degrade'

Note that the line t = s.replace('t', 'ing') doesn’t change the string s, which is still “train”. The method call s.replace('t', 'ing') just has a value, which is the string “ingrain”.

s

'train'

This is the first time we’ve seen methods, but methods are not unique to strings. As we will see shortly, other types of objects can have them.