A thin compatibility layer to use Javascript regular expressions in Python
Project description
js-regex
A thin compatibility layer to use Javascript regular expressions in Python.
Did you know that regular expressions may vary between programming languages?
For example, let's consider the pattern "^abc$"
, which matches the string
"abc"
. But what about the string "abc\n"
? It's also matched in Python,
but not in Javascript!
This and other slight differences can be really important for cross-language
standards like jsonschema
, and that's why js-regex
exists.
How it works
import re
import js_regex
re.compile("^abc$").match("abc\n") # matches, unlike JS
js_regex.compile("^abc$").match("abc\n") # does not match
Internally, js_regex.compile()
replaces JS regex syntax which has a different
meaning in Python with whatever Python regex syntax has the intended meaning.
We also check for constructs which are valid in Python but not JS - such as
named capture groups - and raise an explicit error. Constructs which are valid
in JS but not Python are also an error, because we're still using Python's
re.compile()
function under the hood!
The following table is adapted from this larger version, ommiting other languages and any rows where JS and Python have the same behaviour.
Feature | Javascript | Python | Handling |
---|---|---|---|
\a (bell) |
no | yes | Converted to JS behaviour |
\ca -\cz and \cA -\cZ (control characters) |
yes | no | Converted to JS behaviour |
\d for digits, \w for word chars, \s for whitespace |
ascii | unicode | Converted to JS behaviour (including \D , \W , \S for negated classes) |
$ (end of line/string) |
at end | allows trailing \n |
Converted to JS behaviour |
\A (start of string) |
no | yes | TODO: explicit error, suggest ^ |
\Z (end of string) |
no | yes | TODO: explicit error, suggest $ |
(?<=text) (positive lookbehind) |
no | yes | TODO: explicit error |
(?<!text) (negative lookbehind) |
no | yes | TODO: explicit error |
(?(1)then|else) |
no | yes | TODO: explicit error |
(?(group)then|else) |
no | yes | TODO: explicit error |
(?#comment) |
no | yes | TODO: explicit error |
(?P<name>regex) (named capture group) |
no | yes | TODO: explicit error |
(?P=name) (named backreference) |
no | yes | TODO: explicit error |
Free-spacing / multi-line syntax | no | yes | TODO: explicit error |
(?s) (dot matches newlines) |
no | yes | TODO: explicit error |
(?x) (free-spacing mode) |
no | yes | TODO: explicit error |
(?i) (case insensitive) |
/i only |
yes | TODO: ??? |
(?m) (^ and $ match at line breaks) |
/m only |
yes | TODO: ??? |
Backreferences non-existent groups are an error | no | yes | Follows Python behaviour |
Backreferences to failed groups also fail | no | yes | Follows Python behaviour |
Nested references \1 through \9 |
yes | no | Follows Python behaviour |
Changelog
0.2.0 - 2019-09-28
Convert JS-only syntax to Python equivalent wherever possible.
0.1.0 - 2019-09-28
Initial release, with project setup and a very basic implementation.
Project details
Download files
Download the file for your platform. If you're not sure which to choose, learn more about installing packages.