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Description:

jsregex 1.0.1

js-regex
A 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$").search("abc\n") # matches, unlike JS
js_regex.compile("^abc$").search("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.
This only works for the .search() method - there is no equivalent to
.match() or .fullmatch() for Javascript regular expressions.
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 may also raise 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
Explicit error, use ^ instead

\Z (end of string)
no
yes
Explicit error, use $ instead

(?<=text) (positive lookbehind)
new in ES2018
yes
Allowed

(?<!text) (negative lookbehind)
new in ES2018
yes
Allowed

(?(1)then|else)
no
yes
Explicit error

(?(group)then|else)
no
yes
Explicit error

(?#comment)
no
yes
Explicit error

(?P<name>regex) (Python named capture group)
no
yes
Not detected (yet)

(?P=name) (Python named backreference)
no
yes
Not detected (yet)

(?<name>regex) (JS named capture group)
new in ES2018
no
Error from Python, not translated (yet)

$<name> (JS named backreference)
new in ES2018
no
Error from Python, not translated (yet)

(?i) (case insensitive)
/i only
yes
Explicit error, compile with flags=re.IGNORECASE instead

(?m) (^ and $ match at line breaks)
/m only
yes
Explicit error, compile with flags=re.MULTILINE instead

(?s) (dot matches newlines)
no
yes
Explicit error, compile with flags=re.DOTALL instead

(?x) (free-spacing mode)
no
yes
Explicit error, there is no corresponding mode in Javascript

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

Note that in many cases Python-only regex features would be treated as part of
an ordinary pattern by JS regex engines. Currently we raise an explicit error
on such inputs, but may translate them to have the JS behaviour in a future version.
Changelog
1.0.1 - 2019-10-17

Allow use of native strings on Python 2. This is not actually valid according
to the spec, but it's only going to be around for a few months so whatever.

1.0.0 - 2019-10-04

Now considered feature-complete and stable, as all constructs recommended
for jsonschema patterns are supported and all Python-side incompatibilities
are detected.
Compiled patterns are now cached on Python 3, exactly as for re.compile

0.4.0 - 2019-10-03

Now compatible with Python 2.7 and 3.5, until
their respective EOL dates.

0.3.0 - 2019-09-30

Fixed handling of non-trailing $, e.g. in "^abc$|^def$" both are converted
Added explicit errors for re.LOCALE and re.VERBOSE flags, which have no JS equivalent
Added explicit checks and errors for use of Python-only regex features

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.