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re: Add support for start- and endpos. #14179

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re: Add support for start- and endpos. #14179

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greezybacon
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This adds support to match the CPython re module which supports searching and matching a substring using a start- and end-pos specified in the corresponding Pattern method.

Pattern objects have two additional parameters for the ::search and ::match methods to define the starting and ending position of the subject within the string to be searched.

This allows for searching a sub-string without creating a slice of the string, which is advantageous for performance and also makes inroads for something like the finditer method.

However, one caveat of using the start-pos rather than a slice is that the start anchor (^) remains anchored to the beginning of the text.

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github-actions bot commented Mar 26, 2024 •
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Code size report:

   bare-arm:    +0 +0.000% 
minimal x86:    +0 +0.000% 
   unix x64:  +112 +0.013% standard
      stm32:   +80 +0.020% PYBV10
     mimxrt:   +80 +0.021% TEENSY40
        rp2:   +72 +0.008% RPI_PICO_W
       samd:   +72 +0.027% ADAFRUIT_ITSYBITSY_M4_EXPRESS
  qemu rv32:   +80 +0.018% VIRT_RV32

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codecov bot commented Mar 26, 2024 •
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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.44%. Comparing base (c72a3e5) to head (d2813a1).
Report is 8 commits behind head on master.

Additional details and impacted files 
@@           Coverage Diff           @@
##           master   #14179   +/-   ##
=======================================
  Coverage   98.44%   98.44%           
=======================================
  Files         171      171           
  Lines       22208    22220   +12     
=======================================
+ Hits        21863    21875   +12     
  Misses        345      345

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stinos commented Mar 26, 2024 •
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This adds support to match the CPython re module which supports searching and matching a substring using a start- and end-pos specified in the corresponding Pattern method

Just to be clear: 'match' doesn't mean it's CPython-compatible (and hence the use of a .exp file for the tests)? In that case this feature feels somewhat confusing and hard to discover, and will likely remain underused?

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greezybacon commented Mar 26, 2024 via email •
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I was a bit excited and went ahead and added a finditer implementation as well. It's also aimed at compatibility with CPython's re module. If it should remain, I'd like a little direction on the #define to include support for it. Do we need it? Did I get it in the right place?

@greezybacon greezybacon force-pushed the feature/re-start-end-pos branch from b191a01 to 8c28d63 Compare March 27, 2024 03:08
dpgeorge
dpgeorge reviewed Mar 27, 2024
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extmod/modre.c
}
else if (endpos < startpos) {
endpos = startpos;
}
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Please add a test case that tests this line.

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Thanks, @dpgeorge, I did.

@dpgeorge dpgeorge added the extmod Relates to extmod/ directory in source label Apr 19, 2024
@greezybacon greezybacon force-pushed the feature/re-start-end-pos branch from 5ad16c3 to cf778ac Compare July 18, 2025 14:28
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Sorry, this PR got a bit lost...

I was a bit excited and went ahead and added a finditer implementation as well.

OK, so that increases the scope somewhat of this PR 😅

It would be good to know what the code size impact is for just the start/endpos change. To that end, probably best to keep this PR just for start/endpos (including tests for that), and have a separate PR for finditer. That makes it easier to review.

@greezybacon greezybacon force-pushed the feature/re-start-end-pos branch 2 times, most recently from e602699 to dbe3f83 Compare July 19, 2025 02:07
@greezybacon
re: Add support for start- and endpos.
d2813a1 
Pattern objects have two additional parameters for the ::search and
::match methods to define the starting and ending position of the
subject within the string to be searched.

This allows for searching a sub-string without creating a slice.
However, one caveat of using the start-pos rather than a slice is that
the start anchor (`^`) remains anchored to the beginning of the text.

Signed-off-by: Jared Hancock <jared@greezybacon.me>
@greezybacon greezybacon force-pushed the feature/re-start-end-pos branch from dbe3f83 to d2813a1 Compare July 19, 2025 02:11
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Thanks, @dpgeorge. I really appreciate the review and feedback. I have separated the finditer method into a separate branch and will propose it as a separate PR if this gets merged.

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