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Other Common String Methods in Action

Other string methods have more focused roles—for example, to strip off whitespace at the end of a line of text, perform case conversions, test content, and test for a substring at the end or front:

>>> line = "The knights who say Ni!\n"
>>> line.rstrip()
'The knights who say Ni!'
>>> line.upper()
'THE KNIGHTS WHO SAY NI!\n'
>>> line.isalpha()
False
>>> line.endswith('Ni!\n')
True
>>> line.startswith('The')
True

Alternative techniques can also sometimes be used to achieve the same results as string methods—the in membership operator can be used to test for the presence of a substring, for instance, and length and slicing operations can be used to mimic endswith:

>>> line
'The knights who say Ni!\n'

>>> line.find('Ni') != −1       # Search via method call or expression
True
>>> 'Ni' in line
True

>>> sub = 'Ni!\n'
>>> line.endswith(sub)          # End test via method call or slice
True
>>> line[-len(sub):] == sub
True

See also the format string formatting method described later in this chapter; it provides more advanced substitution tools that combine many operations in a single step.

Again, because there are so many methods available for strings, we won’t look at every one here. You’ll see some additional string examples later in this book, but for more details you can also turn to the Python library manual and other documentation sources, or simply experiment interactively on your own. You can also check the help(S.method) results for a method of any string object S for more hints.

Note that none of the string methods accepts patterns—for pattern-based text processing, you must use the Python re standard library module, an advanced tool that was introduced in Chapter 4 but is mostly outside the scope of this text (one further example appears at the end of Chapter 36). Because of this limitation, though, string methods may sometimes run more quickly than the re module’s tools.