I've had a lot of experience running a compiled regex 1000s of times versus compiling on-the-fly, and have not noticed any perceivable difference. Obviously, this is anecdotal, and certainly not a great argument against compiling, but I've found the difference to be negligible.
EDIT:
After a quick glance at the actual Python 2.5 library code, I see that Python internally compiles AND CACHES regexes whenever you use them anyway (including calls to re.match()), so you're really only changing WHEN the regex gets compiled, and shouldn't be saving much time at all - only the time it takes to check the cache (a key lookup on an internal dict type).
From module re.py (comments are mine):
def match(pattern, string, flags=0):
return _compile(pattern, flags).match(string)
def _compile(*key):
# Does cache check at top of function
cachekey = (type(key[0]),) + key
p = _cache.get(cachekey)
if p is not None: return p
# ...
# Does actual compilation on cache miss
# ...
# Caches compiled regex
if len(_cache) >= _MAXCACHE:
_cache.clear()
_cache[cachekey] = p
return p
I still often pre-compile regular expressions, but only to bind them to a nice, reusable name, not for any expected performance gain.
Answer from Kenan Banks on Stack OverflowGeeksforGeeks
geeksforgeeks.org › python › re-compile-in-python
re.compile() in Python - GeeksforGeeks
July 23, 2025 - The re.compile() method in Python is used to compile a regular expression pattern into a regex object.
Top answer 1 of 16
560
I've had a lot of experience running a compiled regex 1000s of times versus compiling on-the-fly, and have not noticed any perceivable difference. Obviously, this is anecdotal, and certainly not a great argument against compiling, but I've found the difference to be negligible.
EDIT:
After a quick glance at the actual Python 2.5 library code, I see that Python internally compiles AND CACHES regexes whenever you use them anyway (including calls to re.match()), so you're really only changing WHEN the regex gets compiled, and shouldn't be saving much time at all - only the time it takes to check the cache (a key lookup on an internal dict type).
From module re.py (comments are mine):
def match(pattern, string, flags=0):
return _compile(pattern, flags).match(string)
def _compile(*key):
# Does cache check at top of function
cachekey = (type(key[0]),) + key
p = _cache.get(cachekey)
if p is not None: return p
# ...
# Does actual compilation on cache miss
# ...
# Caches compiled regex
if len(_cache) >= _MAXCACHE:
_cache.clear()
_cache[cachekey] = p
return p
I still often pre-compile regular expressions, but only to bind them to a nice, reusable name, not for any expected performance gain.
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183
For me, the biggest benefit to re.compile is being able to separate definition of the regex from its use.
Even a simple expression such as 0|[1-9][0-9]* (integer in base 10 without leading zeros) can be complex enough that you'd rather not have to retype it, check if you made any typos, and later have to recheck if there are typos when you start debugging. Plus, it's nicer to use a variable name such as num or num_b10 than 0|[1-9][0-9]*.
It's certainly possible to store strings and pass them to re.match; however, that's less readable:
num = "..."
# then, much later:
m = re.match(num, input)
Versus compiling:
num = re.compile("...")
# then, much later:
m = num.match(input)
Though it is fairly close, the last line of the second feels more natural and simpler when used repeatedly.
Do you see any reason to use re.compile() when you are working with regular expressions?
There is supposed to be a speedup if you compile a heavily used regexp. You may not see any difference if you just use a non-compiled regexp a few times. If in doubt in your particular case just compare execution times for compiled and non-compiled cases. More on reddit.com
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October 12, 2024When to use re.compile ?
I personally like to compile when I will be doing something often. It is not about performance, but about simplicity. Honestly, it comes down to personal preference More on reddit.com
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June 26, 2018Question about raw strings in re.compile()
Because the re module recognizes the two characters as a new line. You don't put a real new line character(s) in the regex string. More on reddit.com
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February 14, 2025What is the correct syntax for using re.compile in matches?
I'm sorry, I completely misunderstood your request and didn't read properly. I recommend to lookup stuff in the Python documentation for language specific stuff. At least read a basic tutorial about Python 3 (make sure it is not Python 2), which will help you greatly with configuring and doing more in Qtile. Just take the time, maybe a few hours, a few days. So for you actual question and problem, lookup here: https://docs.python.org/3/library/re.html To use a module, you need to import it. There are some nuances in importing stuff, as you can also just import specific parts of the module. That is why it is important to get an understanding in the language of Python. If you want find out more about a module, then lookup it here (in example with the browser search functionality): https://docs.python.org/3/library/index.html . The language reference at https://docs.python.org/3/reference/index.html is not a tutorial or anything, but if you want lookup something specific about the language, then this could be a good starting point. #!/bin/env python3 import re regex = re.compile(r'https://.+(/.+\.png)$') string = 'https://i.imgur.com/S56ia4Y.png' result = regex.match(string) print(result.group(0)) print(result.group(1)) Important: Make sure to lookup the correct version of the documentation, that matches your installed Python version. Look here to see what I mean: https://i.imgur.com/S56ia4Y.png More on reddit.com
5
5
May 14, 202202:18
[regex_02] re.compile pattern - YouTube
07:03
Python Regex Compile [7-Minutes Primer] - YouTube
04:45
Regular Expressions 2018 | #9 re.compile() for efficiency | Python ...
Master Regular Expressions in Python: Unleash Hidden Patterns! ...
58:37
Master Python Regular Expressions in 1 Hour: Complete Guide - YouTube
05:52
Python standard library: Increase regular expression speeds with ...
Scaler
scaler.com › home › topics › re.compile in python
Re.compile in Python - Scaler Topics
March 12, 2024 - The re.compile() in Python is a powerful tool for regex pattern development, allowing you to pre-compile and save patterns for easy reuse. This function improves speed by preventing unnecessary recompilations. It's like having a regex blueprint ready for many searches, with minimal overhead.
Interactive Chaos
interactivechaos.com › en › python › function › recompile
re.compile | Interactive Chaos
May 3, 2021 - Python scenarios · Full name · re.compile · Library · re · Syntax · re.compile(pattern, flags=0) Description · The re.compile function creates a regular expression object by compiling a regular expression pattern, which can be used as a matching pattern in the re.match, re.search, etc.
Reddit
reddit.com › r/learnpython › do you see any reason to use re.compile() when you are working with regular expressions?
r/learnpython on Reddit: Do you see any reason to use re.compile() when you are working with regular expressions?
October 12, 2024 -
beginner here, i don't really see a difference just assigning the regex pattern to a variable. are there some cases where it can be helpful?
Top answer 1 of 5
8
There is supposed to be a speedup if you compile a heavily used regexp. You may not see any difference if you just use a non-compiled regexp a few times. If in doubt in your particular case just compare execution times for compiled and non-compiled cases.
2 of 5
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According to this SO answer there is a 512-item cache. And this cache is totally cleared once you hit the limit (it's not a LRU cache). So for "casual" regex use, compilation isn't needed, but if you are using them intensively that becomes useful.
GeeksforGeeks
geeksforgeeks.org › python › python-re-compile
Python - re.compile() - GeeksforGeeks
July 23, 2025 - import re # Compile a case-insensitive regex pattern = re.compile(r'hello', re.IGNORECASE) # Use the compiled pattern text = "Hello, GeeksforGeeks!" match = pattern.search(text) if match: print(f" {match.group()}")
PYnative
pynative.com › home › python › regex › python compile regex pattern using re.compile()
Python Compile Regex Pattern using re.compile()
April 2, 2021 - Python’s re.compile() method is used to compile a regular expression pattern provided as a string into a regex pattern object (re.Pattern).
TutorialsPoint
tutorialspoint.com › Why-do-we-use-re-compile-method-in-Python-regular-expression
Python re.compile() method
January 24, 2025 - import re pattern = re.compile(r'^\d+', re.MULTILINE | re.IGNORECASE) text = """123abc 456def 789ghi""" matches = pattern.findall(text) print(matches) ... Here this example uses the re.VERBOSE flag which allows us to write more readable regular expressions with comments and whitespace − · import re pattern = re.compile(r""" \d+ # One or more digits \s* # Zero or more whitespace characters """, re.VERBOSE) matches = pattern.findall('123 abc 456 def') print(matches)
Python Academy
python-academy.org › functions › re.compile
re.compile — Python Function Reference
A comprehensive guide to Python functions, with examples. Find out how the re.compile function works in Python. Compile a regular expression pattern into a regular expression object, which can be used for matching using its match(), search() and other methods.
Byu
labs.acme.byu.edu › DataScienceEssentials › RegularExpressions › RegularExpressions.html
Regular Expressions — ACME Labs
The function re.compile() takes in a regular expression string and returns a corresponding pattern object, which has methods for determining if and how other strings match the pattern. You can think of the re.compile object as a box with a certain shape cut out of the bottom.
TechGeekBuzz
techgeekbuzz.com › home › blog › python › python compile regex pattern using re.compile()
Python Compile Regex Pattern using re.compile()
Then we also define an identifier targeted string string from which we want to match the pattern and extract the information. The re.compile(pattern) statement creates a regular expression object out of the specified pattern.
Python documentation
docs.python.org › 3 › library › re.html
re — Regular expression operations — Python 3.14.7 ...
The solution is to use Python’s raw string notation for regular expression patterns; backslashes are not handled in any special way in a string literal prefixed with 'r'. So r"\n" is a two-character string containing '\' and 'n', while "\n" is a one-character string containing a newline. Usually patterns will be expressed in Python code using this raw string notation. It is important to note that most regular expression operations are available as module-level functions and methods on compiled regular expressions.
Python for Network Engineers
pyneng.readthedocs.io › en › latest › book › 15_module_re › compile.html
Compile function - Python for network engineers
import re regex = re.compile(r'Host \S+ ' r'in vlan (\d+) ' r'is flapping between port ' r'(\S+) and port (\S+)') ports = set() with open('log.txt') as f: for m in regex.finditer(f.read()): vlan = m.group(1) ports.add(m.group(2)) ports.add(m.group(3)) print('Loop between ports {} in VLAN {}'.format(', '.join(ports), vlan))
ZetCode
zetcode.com › python › regex-compile-function
Python re.compile - Mastering Regular Expression Compilation
The re.compile function is a fundamental part of Python's re module. It transforms a regular expression pattern into a regex object that can be reused multiple times.
Medium
nowitsanurag.medium.com › regular-expression-in-python-f42483e80daa
Regular Expression in Python. Regex | by Anurag | Medium
January 11, 2023 - The re.compile() function takes a string as an argument and returns a regular expression object. The r in front of the string is called a raw string, which is used to ignore escape characters.
Beautiful Soup
tedboy.github.io › python_stdlib › generated › generated › re.compile.html
re.compile() — Python Standard Library
Compile a regular expression pattern, returning a pattern object.
Finxter
blog.finxter.com › home › learn python blog › python regex compile
Python Regex Compile – Be on the Right Side of Change
November 17, 2020 - ... The re.compile(patterns, flags) method returns a regular expression object. You may ask (and rightly so): Python internally creates a regular expression object (from the Pattern class) to prepare the pattern matching process.
Reddit
reddit.com › r/learnpython › when to use re.compile ?
r/learnpython on Reddit: When to use re.compile ?
June 26, 2018 -
I've been learning how to use the re module in python. Methods like findall, search, finditer all make sense in terms of their usability and scope, but I'm not sure of when using re.compile would be an optimal solution. Could someone give any insights into this?
Top answer 1 of 2
4
I personally like to compile when I will be doing something often. It is not about performance, but about simplicity. Honestly, it comes down to personal preference
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I think you don't need to compile it, if you do it for performance. I read time ago Python does save it in the cache for you. Yeah, here it is
DaniWeb
daniweb.com › programming › software-development › threads › 131590 › search-and-replace-with-re-compile
python - Search and replace with re:compile(....) [SOLVED] | DaniWeb
Ok, I would like to use a regular expression that I create dynamically to search and replace words in a file. For instance: import re fl = re.compile('abc|def|ghi') ts = 'xyz abc mno def'
Python3
python3.info › intermediate › regex › re-compile.html
7.29. Regex RE Compile — Python - from None to AI
Used when pattern is reused (especially in the loop) Prepare: >>> x = re.compile(pattern) Usage: >>> x.findall(string) >>> x.match(string) >>> x.search(string) >>> import re · >>> DATA = [ ... 'alice@example.com', ... 'bob@example.com', ... 'carol@example.com', ... 'dave@example.org', ... 'eve@example.org', ... 'mallory@example.net', ... ] Python will compile pattern during every loop iteration ·