.. -=- Python RegEx through the ages, Appendix C -=NO=-=MENU=- -=-

= Python RegEx through the ages, Appendix C: Summary table =

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Colliding names used by multiple non-interchangable modules (`regex` and `pcre`) are preceded by a disambiguating numerical superscript. 

| Included with    |Base API|Engine|Main module name|C module name|Other modules|Notes|
|------------------|---|---|---|---|---|---|
| 0.9.0–0.9.1|First (`exec`)|Henry Spencer|`regexp`|`regexp`||Posix Extended format. First public release of Python. Very simple API.|
| 0.9.2–0.9.4|First (`match`)|Henry Spencer|`regexp`|`regexp`||`exec` method renamed to `match`.|
| 0.9.5            |Second|GNU|(^(1st)^)`regex`|(^(1st)^)`regex`|`regex_syntax`|Emacs-style format by default, but changeable with flags.|
| 0.9.6–2.4  |Second|Ylönen based|(^(1st)^)`regex`|(^(1st)^)`regex`|`regex_syntax`, later also `regsub`|Changed to engine written by Tatu Ylönen. Emitting DeprecationWarning since 2.1, finally removed in 2.5.0alpha1.|
| 0.9.5–1.4  |First (`match`)|(same as (^(1st)^)`regex`)|`regexp`|(^(1st)^)`regex`| |Wrapper around the contemporary (^(1st)^)`regex` module. Module removed in 1.5.0beta1.|
| 1.5.0            |Third|Ylönen based (bytecode), custom (parsing)|`re` or `re1`|`reop`| |Perl-style format. New thread-safe API defined. Introduced as `re` in 1.5.0alpha3, implementation never fully debugged before it was superseded in 1.5.0alpha4. Retained as `re1` for the 1.5.0 release, removed before 1.5.1.|
| 1.5–2.3    |Third|PCRE (old)|`re` or `pre`|(^(1st)^)`pcre`||Introduced in 1.5.0alpha4 using what was then (late 1990s) a contemporary PCRE library. In particular, Unicode regular expressions were not yet supported. Renamed to `pre` in Python 2.(^[†](#obelisk)^) Removed in Python 2.4.|
| 1.6(^[†](#obelisk)^)–present|Third|SecretLabs based|`sre` or `re`|`_sre`|`sre_compile`, `sre_parse`, `sre_constants`|Introduced with Python 2(^[†](#obelisk)^) as `sre` due to the need for a `re` implementation that supported Unicode regular expressions. Initially used a recursive matching scheme, this was changed in Python 2.4.0alpha1. Importing as `sre` deprecated in Python 2.5, only availabile as `re` in Python 3.x.|
| PyPI `python-pcre`|mostly Third|PCRE|(^(2nd)^)`pcre`|`_pcre`||Extension binding by Arkadiusz Wahlig. Uses the third API except for substitution format string syntax, and can be configured to use the third-API syntax there too. Lacks the scanner APIs and DEBUG and LOCALE flags of the third API. Current PCRE does support Unicode regular expressions; note the name collision.|
| Planned for future inclusion; PyPI `regex`|Third with extensions|SecretLabs based|(^(2nd)^)`regex`|`_regex`|`_regex_core`|Extension by Matthew Barnett, forked from `re` (`sre`). Prominent enough to get a mention in the documentation and ["in principle approval for eventual stdlib inclusion"](https://wiki.python.org/moin/Python2orPython3#Supporting_Python_2_and_Python_3_in_a_common_code_base). Note the name collision with the second API. Backward-incompatibile behaviour fixes behind a version switch selectable in regex syntax and in API.|

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† Python 1.6 is basically the state of Python 2 at the point that Guido left CNRI, released under contractual obligation or something similar: it incorporates many but not all distinctively 2.x features, it is accordingly not a true Python 1.x release; hence, "What's new in Python 2.0" compares it with Python 1.5.2.