Improvements in regular expression doc #114357
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@@ -83,6 +83,12 @@ characters, so ``last`` matches the string ``'last'``. (In the rest of this | |||||
| section, we'll write RE's in ``this special style``, usually without quotes, and | ||||||
| strings to be matched ``'in single quotes'``.) | ||||||
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| .. _re-special-characters: | ||||||
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| Special characters | ||||||
| ^^^^^^^^^^^^^^^^^^ | ||||||
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| Some characters, like ``'|'`` or ``'('``, are special. Special | ||||||
| characters either stand for classes of ordinary characters, or affect | ||||||
| how the regular expressions around them are interpreted. | ||||||
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@@ -93,7 +99,6 @@ directly nested. This avoids ambiguity with the non-greedy modifier suffix | |||||
| repetition to an inner repetition, parentheses may be used. For example, | ||||||
| the expression ``(?:a{6})*`` matches any multiple of six ``'a'`` characters. | ||||||
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| The special characters are: | ||||||
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| .. index:: single: . (dot); in regular expressions | ||||||
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@@ -114,31 +119,33 @@ The special characters are: | |||||
| ``$`` | ||||||
| Matches the end of the string or just before the newline at the end of the | ||||||
| string, and in :const:`MULTILINE` mode also matches before a newline. ``foo`` | ||||||
| matches both ``'foo'`` and ``'foobar'``, while the regular expression ``foo$`` | ||||||
| matches | ||||||
| only 'foo'. More interestingly, searching for ``foo.$`` in ``'foo1\nfoo2\n'`` | ||||||
| matches 'foo2' normally, but ``'foo1'`` in :const:`MULTILINE` mode; searching | ||||||
| for | ||||||
| a single ``$`` in ``'foo\n'`` will find two (empty) matches: one just before | ||||||
| the newline, and one at the end of the string. | ||||||
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| .. index:: single: * (asterisk); in regular expressions | ||||||
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| ``*`` | ||||||
| Causes the resulting RE to match 0 or more repetitions of the preceding RE, as | ||||||
| many repetitions as are possible. ``ab*`` will match ``'a'``, ``'ab'``, or | ||||||
| ``'a'`` followed by any number of ``'b'`` s. | ||||||
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| ``'a'`` followed by any number of ``'b'`` s. | |
| ``'a'`` followed by any number of ``'b'``\ s. |
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Can we call them all escape sequences? Differentiates better from the multi-character “special character” sequences above.
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Are there other subtypes of special characters? What if about subsections?
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I suggest change the next heading to something like String literal escapes, and change this heading from Special sequences to Escape sequences.
These are the types of the special characters I can think of for REs:
- The single-character metacharacters:
$, *, [, ], \, etc, as listed in the how-to https://cpython-previews--114357.org.readthedocs.build/en/114357/howto/regex.html#matching-characters - Multicharacter syntax built with the metacharacters, like *?, {m,n} and the bracketed extension notation (?. . .)
- “Special sequences” a.k.a. escape sequences, which begin with a backslash. These could be subdivided into
- Non-alphanumeric, for escaping metacharacters and other syntax:
\$, \*, \\, \', \", etc - Group references \1–\99
- Alphanumeric sequences that specify locations to match, or categories of characters: \A, \b, \d, etc
- String literal escapes:
\n, \\, \N{. . .}, \0–\777, etc. Excludes \b and\<newline>.
- Non-alphanumeric, for escaping metacharacters and other syntax:
- Characters only special in “verbose” expressions: whitespace and #
- Additional backslash sequence for re.sub templates: \g<. . .>
- Special characters inside square-bracketed classes/sets [. . .], especially -, ^, ], \b, and reserved [, &&, etc
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To be consistent with other additions, 'foo' above and 'foo2' here should be backticked. But see review summary.
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Done.