Python Learning Note 21 (regular expression)

Regular expression pattern:

Except for the control character (+?. * ^ $ () [] {} | \), all characters match themselves. You can escape the control character by using the backslash before it.

The following table lists the available regular expression syntax in Python:

Mode	Description
^	The beginning of the match
$	Match end of Line
.	Matches any single character except the line break. This is true with the-m option allowing it to match the line break.
[...]	Match any single character in parentheses
[^...]	Match any single character not in parentheses
Tel	Matches 0 or more occurrences of the preceding expression.
Re+	Matches 1 or more previously occurring expressions.
Re?	Matches an expression that appears before 0 or 1.
re{N}	Exactly matches the number of n preceding expressions.
re{N,}	Matches n or more occurrences of the above expression.
re{N, m}	Matches at least n times and most of the preceding expressions appear m times.
a| B	Match A or B.
(RE)	Group regular expressions and remember the matching text.
(? imx)	Temporarily toggles the options on the I, M, or x regular expressions. If in parentheses, only the area is affected.
(?-imx)	Temporarily turn off the option to toggle I, M, or x regular expressions. If in parentheses, only the area is affected.
(?: RE)	The group regular expression does not match the remembered text.
(? imx:re)	Temporarily switch the options in the upper I, M, or x brackets.
(?-imx:re)	Temporarily turn off toggle I, M, or x brackets within the options.
(?#...)	Comments
(? = re)	Specifies the mode location used, without a range.
(?! Re)	Specifies the use mode to reverse the position without a range.
(?> re)	Match independent patterns without tracking backwards.
\w	Matches a word character.
\w	Match non-word characters
\s	Matched blanks, equivalent to [\ t\ñ\ r\ F]
\s	Match non-whitespace
\d	Matches the number. equivalent to [0-9]
\d	Match non-numeric
\a	Match the start of a string
\z	Matches the end of the string. If a newline character exists, it just matches before the line breaks
\z	Match the end of a string
\g	Match point, end of last match
\b	Matches the word boundary outside the parentheses. Match backspace (0x08), in parentheses
\b	Match non-word boundaries
\ n, \ t, etc.	Match line break, carriage return, tab, etc.
\1...\9	A sub-expression that matches the nth grouping.
\10	Matches if it already matches the sub-expression of nth grouping. Otherwise, it refers to the octal representation of a character code.

Example literal characters for regular expressions:

Example	Description
Python	Match "Python".

Character class:

Example	Description
[Pp]ython	Match "python" or "python"
Rub[ye]	Match "Ruby" or "Rube"
[Aeiou]	Match any one lowercase vowel
[0-9]	Match any number; if [0123456789]
[A-z]	Matches any lowercase ASCII letter
[A-z]	Matches any uppercase ASCII letter
[A-za-z0-9]	Match any of the above
[^aeiou]	Match any not lowercase vowels
[^0-9]	Match any non-numeric

Special Character classes:

Example	Description
.	Match any character except for a line break
\d	Match a number: [0-9]
\d	Match a non-numeric: [^0-9]
\s	Match a white space character: [\ t\ r\ñ\ F]
\s	Matching non-whitespace: [^\ t\ r\ñ\ F]
\w	Match a word character: [a-za-z0-9 _]
\w	Match non-word characters: [^ a-za-z0-9 _]

Repeat case:

Example	Description
Ruby?	Match "rub" or "Ruby": Y is optional
ruby*	Match "rub" plus 0 or more Ys
ruby+	Match "rub" plus 1 or more YS
\D{3}	Match 3 numbers exactly
\d{3,}	Match 3 or more numbers exactly
\d{3,5}	Match a 3,4 or 5 digits

Non-greedy repetition:

Match minimum number of repetitions:

Example	Description
<.*>	Greedy repetition: matching "<python>perl>"
<.*?>	Non-greedy: Match "<python>" in "<python>perl>"

Grouping using parentheses:

Example	Description
\d\d+	Do not group: + Repeat \d
(\d\d) +	Group: + Repeat \d\d pairs
([Pp]ython (,)?) +	Match "Python", "python, Python, Python," and so on.

Reverse reference:

Match again?? Previously matched groups:

Example	Description
([Pp]) ython&\1ails	Match Python&pails or Python&pails
([‘"]) [^\1]*\1	Single or double quote string. \1 matches the first set of matches. \2 matches the second set of matches, and so on.

Alternative scenarios:

Example	Description
Python|perl	Match "Python" or "Perl"
Rub (Y|le))	Match "Ruby" or "ruble"
Python (!+|\?)	"Python" followed by one or more! or one?

Anchor Point:

Need to specify a matching location

Example	Description
^python	Match "Python" at the beginning of a string or inner line
python$	Match "Python" string or end of line
\apython	Match "Python" at the beginning of the string
Python\z	Match "Python" at the end of the string
\bpython\b	Match "Python" at word boundaries
\brub\b	\b Non-word boundaries: matches "rub", "Rube" and "Ruby", but not individually
Python (? =!)	Match "Python" if the following exclamation mark
Python (?!!)	Match "Python" if not followed by an exclamation point

Special syntax with parentheses:

Example	Description
R (? #comment)	Conforms to "R". All the rest are notes.
R (? i) Uby	Case insensitive when "Uby" is matched
R (? i:uby)	The same as above
Rub (?: Y|le))	Only groups without creating a \1 reverse reference

Python Learning Note 21 (regular expression)