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.

In [1]:
"loud".upper()
Out[1]:
'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.

In [2]:
'hitchhiker'.replace('hi', 'ma')
Out[2]:
'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.

In [3]:
s = "train"
t = s.replace('t', 'ing')
u = t.replace('in', 'de')
u
Out[3]:
'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".

In [4]:
s
Out[4]:
'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.