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Python Regular Expressions in Python Introduction to Regular Expressions Escape Hatches

Josh Keenan
Josh Keenan
19,528 Points

Regular expressions uses

Just started the course and I was wondering whether they can be used in databases and variables like dictionaries, lists or tuples. Thanks Guys!

4 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,064 Points

If by "can be used it" you mean stored within, then yes, to some degree. In lists and dictionaries, regex can be held like any other object.

In [1]: import re

In [2]: pat1 = re.compile(r'\w+')

In [3]: pat2 = re.compile(r'\d+')

In [4]: pats = [pat1, pat2]

In [6]: s1 = "this is a stirng with 01234 and ?##***882"

In [9]: pats[0]
Out[9]: re.compile(r'\w+')

In [11]: pats[0].findall(s1)
Out[11]: ['this', 'is', 'a', 'stirng', 'with', '01234', 'and', '882']

In [12]: pats[1].findall(s1)
Out[12]: ['01234', '882']

In [13]: pat_dict = { 'words': pat1, 'numbers': pat2 }

In [15]: for name, pattern in pat_dict.items():
    print("{} in s1 are {}".format(name, pattern.findall(s1)))
   ....:     
numbers in s1 are ['01234', '882']
words in s1 are ['this', 'is', 'a', 'stirng', 'with', '01234', 'and', '882']

A regexp can be stored in databases if properly serialized to match the limitations of the database format. It can also be stored by using the pattern string as it's value, then recreated from it stored value when needed.

In [19]: pat_dict['words'].pattern
Out[19]: '\\w+'

Good answers here already, but if you're wondering if you can do a 'find and replace' sort of action within a list, dict, tuple, or external database, then it's more a case of 'sort of'... Regex is really only used on strings or text, wherever that text may reside.

So you could, for example, get a list of the key names in a dict, and then iterate/loop over them and use regex on each one to determine if it matches your expression.

You can't however, just apply a regex function to an entire list/dict/tuple.

As for a database, it depends on which type of database you're using, but some support selecting rows matching a regular expression:

Bart Bruneel
Bart Bruneel
27,212 Points

Hey Josh,

Most people use regular expressions to search for (and maybe) replace specific things in large text-files and in writing web scrapers (there is currently a good course going on on Coursera about python and web scrapers if you are interested). I think you can also use regex to query databases. In Django, simple regexes are used to write views. Of course regexes are compatible with lists, dictionaries and tuples. For example, the re.findall method will return a list.