Real Python: Regular Expressions: Regexes in Python (Part 2)

In the previous tutorial in this series, you covered a lot of ground. You saw how to use re.search() to perform pattern matching with regexes in Python and learned about the many regex metacharacters and parsing flags that you can use to fine-tune your pattern-matching capabilities.

But as great as all that is, the re module has much more to offer.

In this tutorial, you’ll:

• Explore more functions, beyond re.search(), that the re module provides
• Learn when and how to precompile a regex in Python into a regular expression object
• Discover useful things that you can do with the match object returned by the functions in the re module

Ready? Let’s dig in!

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re Module Functions

In addition to re.search(), the re module contains several other functions to help you perform regex-related tasks.

Note: You saw in the previous tutorial that re.search() can take an optional <flags> argument, which specifies flags that modify parsing behavior. All the functions shown below, with the exception of re.escape(), support the <flags> argument in the same way.

You can specify <flags> as either a positional argument or a keyword argument:

re.search(<regex>, <string>, <flags>)
re.search(<regex>, <string>, flags=<flags>)

The default for <flags> is always 0, which indicates no special modification of matching behavior. Remember from the discussion of flags in the previous tutorial that the re.UNICODE flag is always set by default.

The available regex functions in the Python re module fall into the following three categories:

1. Searching functions
2. Substitution functions
3. Utility functions

The following sections explain these functions in more detail.

Searching Functions

Searching functions scan a search string for one or more matches of the specified regex:

Function	Description
re.search()	Scans a string for a regex match
re.match()	Looks for a regex match at the beginning of a string
re.fullmatch()	Looks for a regex match on an entire string
re.findall()	Returns a list of all regex matches in a string
re.finditer()	Returns an iterator that yields regex matches from a string

As you can see from the table, these functions are similar to one another. But each one tweaks the searching functionality in its own way.

re.search(<regex>, <string>, flags=0)

Scans a string for a regex match.

If you worked through the previous tutorial in this series, then you should be well familiar with this function by now. re.search(<regex>, <string>) looks for any location in <string> where <regex> matches:

>>>

>>> re.search(r'(\d+)', 'foo123bar')
<_sre.SRE_Match object; span=(3, 6), match='123'>
>>> re.search(r'[a-z]+', '123FOO456', flags=re.IGNORECASE)
<_sre.SRE_Match object; span=(3, 6), match='FOO'>

>>> print(re.search(r'\d+', 'foo.bar'))
None

The function returns a match object if it finds a match and None otherwise.

re.match(<regex>, <string>, flags=0)

Looks for a regex match at the beginning of a string.

Read the full article at https://realpython.com/regex-python-part-2/ »

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