When using the re2 Python bindings, replacing the anchor "$" with re2.subn inserts the replacement twice

[benediktschlager]

I observed that when using the re2 Python bindings, $ replaces the end of the string twice.

What is the current behavior?

This test case fails with the result being "Hello WorldEOSEOS".

import re2

def test_re2_dollar_sign():
    end_of_string = re2.compile("$")
    (result, matches) = end_of_string.subn("EOS", "Hello World")

    assert result == "Hello WorldEOS"
    assert matches == 1

What is the desired behavior?

The result should be "Hello WorldEOS".

I'm using google-re2 in version 1.1.20251105 and Python version 3.11.2.

[MajorTanya]

Can confirm that this also happens on 3.14.2 so it's not quirk in 3.11 interaction or something:

(ran with pytest)

    def test_re2_dollar_sign():
        end_of_string = re2.compile("$")
        result, matches = end_of_string.subn("EOS", "Hello World")
    
>       assert result == "Hello WorldEOS"
E       AssertionError: assert 'Hello WorldEOSEOS' == 'Hello WorldEOS'
E         
E         - Hello WorldEOS
E         + Hello WorldEOSEOS
E         ?               +++