Interactive TUI app with 100+ Python re(gex)? exercises (github.com)
from learnbyexample@programming.dev to python@programming.dev on 23 Jul 2024 13:03
https://programming.dev/post/17233192

I wrote a TUI application to help you practice Python regular expressions. There are more than 100 exercises covering both the builtin re and third-party regex module.

If you have pipx, use pipx install regexexercises to install the app. See the repo for source code and other details.

#python

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alyth@lemmy.world on 23 Jul 2024 18:33 collapse

Thanks for sharing this. I took the time to read through the documentation of the re module. Here’s my review of the functions.

Useful:

  • re.finditer returns an iterator over all Match objects
  • re.search returns the first Match object or None if there are no matches.
  • r’’ use raw strings for patters so you don’t have to worry about backslashes
  • the optional flags argument modifies the behaviour (case insensitive, multiline)

Utility:

  • re.sub replace each match in the string
  • re.split split a string by a regular expression

The Match object:

  • match.groups(0) returns the portion of text matched by the pattern
  • match.groups(1) returns the first capturing group
  • match.groups(2) returns the second capturing group, and so on

I don’t understand why these exist:

  • re.match like search, but only matches at the beginning of the string. why not just use ‘^’ or ‘\A’ in the pattern you pass to ‘search’?
  • re.fullmatch like ‘search’, but only if the full string matches. Why not just use ‘\A’ and ‘\Z’ in the pattern you pass to ‘search’?
  • re.findall Returns all matches. It seems like a shitty version of ‘finditer’. The function has three different return types which depend on the pattern you pattern you pass to the function. Who wants to work with that?
hades@lemm.ee on 24 Jul 2024 07:31 collapse

I would argue that having distinct match and search helps readability. The difference between match(‘((([0-9]±[0-9]+)|([0-9]+))[,]?)+[^,]’, s) and search(‘((([0-9]±[0-9]+)|([0-9]+))[,]?)+[^,]’, s) is clear without the need for me to parse the regular expression myself. It also helps code reuse. Consider that you have PHONE_NUMBER_REGEX defined somewhere. If you only had a method to “search” but not to “match”, you would have to do something like search(f"\A{PHONE_NUMBER_REGEX}\Z", s), which is error-prone and less readable. Most likely you would end up having at least two sets of precompiled regex objects (i.e. PHONE_NUMBER_REGEX and PHONE_NUMBER_FULLMATCH_REGEX). It is also a fairly common practice in other languages’ regex libraries (cf. [1,2]). Golang, which is usually very reserved in the number of ways to express the same thing, has 16 different matching methods[3].

Regarding re.findall, I see what you mean, however I don’t agree with your conclusions. I think it is a useful convenience method that improves readability in many cases. I’ve found these usages from my code, and I’m quite happy that this method was available[4]:

digits = [digit_map[digit] for digit in re.findall("(?=(one|two|three|four|five|six|seven|eight|nine|[0-9]))", line)]
[(minutes, seconds)] = re.findall(r"You have (?:(\d+)m )?(\d+)s left to wait", text)

[1] docs.oracle.com/javase/7/docs/api/…/Matcher.html

[2] en.cppreference.com/w/cpp/regex

[3] pkg.go.dev/regexp

[4] github.com/search?q=repo%3Ahades%2Faoc23 findall&…

alyth@lemmy.world on 24 Jul 2024 08:20 collapse

Thank you for the very thorough reply! This is kind of high quality stuff you love to see on Lemmy. Your use cases seem very valid.