Charming the Python: RegEx

30 Days of Python (21 Part Series)

1 Charming the Python: the basic basics
2 Charming the Python: Builtins and Variables
… 17 more parts…
3 Charming the Python: Boolean & Operators
4 Charming the Python: Strings
5 Charming the Python: Lists
6 Charming the Python: Tuples
7 Charming the Python: Sets
8 Charming the Python: Dictionaries
9 Charming the Python: Data Structures
10 Charming the Python: Conditionals
11 Charming the Python: Loops
12 Charming the Python: Functions
13 Charming the Python: Modules
14 Charming the Python: List Comprehension
15 Charm the Python: Lambdas
16 Charming the Python: Error Types
17 Charming the Python: datetime
18 Charming the Python: Exception Handling
19 Charming the Python: RegEx
20 Charming the Python: File Handling
21 Charming the Python: Classes & Methods pt 1

If coding tutorials with math examples are the bane of your existence, keep reading. This series uses relatable examples like dogs and cats.

Regular Expression (RegEx)

Regular Expression is often referred to as RegEx or regex. Regex is used to search for and find patterns. Regular expressions are a sequence of characters used to define search patterns.

If you’ve ever used ctrl+f to find or find + replace, you’ve used regex.

Take a look at this screenshot. I have searched for every instance of ‘ dog’ in the file. Including the space at thee beginning made sure we only got words that start with ‘dog’. It ignores everything after the search sequence as I didn’t desire to see that. In this case I could use replace to use ‘canine’ or ‘snuggle bug’ instead of ‘dog’.

To use RegEx, start by importing module re

import re

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Common Functions

There are quite a few functions in the regex module. I’ll dig into a few of the more common ones.

re.match()

Returns only the first thing that matches at the beginning of the first line of a string

# syntax re.match(pattern, string, flags=0)

# example >>> import re

>>> dating_site_hobbies = "long walks on the beach and dogs"
>>> match = re.match("long walks", dating_site_hobbies, re.I)  # re.I makes the seach case insensitive >>> print(match)
<re.Match object; span=(0, 10), match='long walks'>

# fails because it's not the beginning of the string >>> match_fail = re.match("dogs", dating_site_hobbies, re.I)
>>> print(match_fail)
None

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In this case, if I was searching for similar likes on a dating site, I wouldn’t care if the word was the first thing in the string of hobbies.

re.search()

Returns anything that matches, no matter where it is in a string

# syntax re.search(pattern, string, flags=0)

# example >>> import re

>>> dating_site_hobbies = "long walks on the beach and dogs"
>>> search = re.search("dogs", dating_site_hobbies, re.I)  # re.I makes the seach case insensitive >>> print(search)
<re.Match object; span=(28, 32), match='dogs'> # span is telling us what characters the search term is at 
# fails because the search term isn't in the hobbies >>> search_fail = re.search("cats", dating_site_hobbies, re.I)
>>> print(search_fail)
None

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re.findall()

Returns list with all matches

# syntax re.findall(pattern, string, flags=0)

# example >>> import re

>>> research_paper_submission = "all the things that were written down to show that I know what I was learning in school"
>>> matches = re.findall("that", research_paper_submission, re.I)  # re.I makes the seach case insensitive 
>>> print(matches)
['that', 'that']

# fails because the search term isn't in the paper >>> matches_fail = re.findall("dog", research_paper_submission, re.I)
>>> print(matches_fail)
[] # prints empty list of no matches because the paper wasn't about dogs 

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re.sub()

Replaces one or many matches with a string
Like ctrl+f then replace

In school, I had a professor suggest I eliminate the use of the word ‘that’. To do this after I’ve written my paper, I could use the following code.

# syntax re.sub(pattern, repl, string, count=0 flags=0)

# example >>> import re

>>> research_paper_submission = "the things that were written down to show that I know what I was learning at school"
>>> matches = re.sub('that', '', research_paper_submission)

>>> print(matches)
the things  were written down to show  I know what I was learning at school

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MetaCharacters

https://www.programiz.com/python-programming/regex

NOTE: if you know how to get pipes, |, to show in a table, please let me know. The last row of this table is messed up because I don’t know how to make it work.

I highly suggest Regex One for practicing your understanding of regex.

Some reference stuff

#regex #regularexpressions

As always, refer to the Python docs for more detailed information

Here’s a cheat sheet worth bookmarking and another thing worth looking at.

Series loosely based on

#python #javascript #react #mongodb

30 Days of Python (21 Part Series)

1 Charming the Python: the basic basics
2 Charming the Python: Builtins and Variables
… 17 more parts…
3 Charming the Python: Boolean & Operators
4 Charming the Python: Strings
5 Charming the Python: Lists
6 Charming the Python: Tuples
7 Charming the Python: Sets
8 Charming the Python: Dictionaries
9 Charming the Python: Data Structures
10 Charming the Python: Conditionals
11 Charming the Python: Loops
12 Charming the Python: Functions
13 Charming the Python: Modules
14 Charming the Python: List Comprehension
15 Charm the Python: Lambdas
16 Charming the Python: Error Types
17 Charming the Python: datetime
18 Charming the Python: Exception Handling
19 Charming the Python: RegEx
20 Charming the Python: File Handling
21 Charming the Python: Classes & Methods pt 1

原文链接：Charming the Python: RegEx