Regular expressionn are a formalism to describe sets of strings. They
can be used to check whether a string matches a given pattern, for
exstracting parts of strings, or substituting part of strings in a
way that is much more powerful and flexible than the str methods
for those purposes.
regexes.ipynb: Jupiter notebook illustrating various aspects of using regular expressions in string-related tasks. This conveys the flavor, rather than being a comprehensive introduction.
More information on regular expressions can be found in the Python introduction slides.