8.10. Syntax Extension¶
In other programming languages
PCRE - Perl Compatible Regular Expressions
8.10.1. Future¶
Since Python 3.11
Atomic grouping
((?>...))and possessive quantifiers (*+,++,?+,{m,n}+) are now supported in regular expressions.
8.10.2. Named Ranges¶
[:allnum:]- Alphabetic and numeric character[a-zA-Z0-9][:alpha:]- Alphabetic character[a-zA-Z][:alnum:]- Alphabetic and numeric character[a-zA-Z0-9][:alpha:]- Alphabetic character[a-zA-Z][:blank:]- Space or tab[:cntrl:]- Control character[:digit:]- Digit[:graph:]- Non-blank character (excludes spaces, control characters, and similar)[:lower:]- Lowercase alphabetical character[:print:]- Like [:graph:], but includes the space character[:punct:]- Punctuation character[:space:]- Whitespace character ([:blank:], newline, carriage return, etc.)[:upper:]- Uppercase alphabetical[:xdigit:]- Digit allowed in a hexadecimal number (i.e., 0-9a-fA-F)[:word:]- A character in one of the following Unicode general categories Letter, Mark, Number, Connector_Punctuation[:ascii:]- A character in the ASCII character set
In Python those Named Ranges does not work. String [:alpha:] will be
interpreted literally as either: : or a or l or p or h
or a.
>>> import re
>>> TEXT = 'hello world'
>>>
>>>
>>> re.findall('[:allnum:]', TEXT)
['l', 'l', 'l']
>>>
>>> re.findall('[:alpha:]', TEXT)
['h', 'l', 'l', 'l']
8.10.3. Range¶
[a-Z]==[a-zA-Z][a-9]==[a-zA-Z0-9]Works in other languages, but not in Python
>>> import re
>>> TEXT = 'hello world'
>>>
>>>
>>> re.findall('[a-Z]', TEXT)
Traceback (most recent call last):
re.error: bad character range a-Z at position 1
>>>
>>> re.findall('[a-9]', TEXT)
Traceback (most recent call last):
re.error: bad character range a-9 at position 1
8.10.4. Group Backreference¶
$1==\1
>>> HTML = '<span>Hello World</span>'
>>> re.findall('<(?P<tag>.+)>(?:.+)</(?P=tag)>', HTML)
['span']
8.10.5. References¶
- 1
Munroe, R. How Standards Proliferate. Year: 2022. Retrieved: 2022-04-27. URL: https://xkcd.com/927/