Python Sixth Week Study notes (2)

Regular expressions Basic syntax meta-character

Code	Description	Example
.	Match any character except for a line break
[ABC]	The character set can only represent one character position. Match any one of the characters contained
[^ABC]	The character set can only represent one character position. Matches any character that drops a character within a collection
[A-z]	A character range, a collection that represents a character position that matches any one of the characters contained in the
[^a-z]	A character range, a collection that represents a character position that matches any character that drops a character within a collection
\b	Match the boundaries of a word
\b	Do not match the boundaries of a word
\d	equals [0-9] matches a digit
\d	Equivalent [^0-9] matches a non-numeric
\s	Matches 1-bit whitespace characters, including line breaks, tabs, space equivalents [\f\r\n\t\v]
\s	Match 1-bit non-whitespace characters
\w	Equivalent [a-za-z0-9_] contains Chinese
\w	Match characters outside of \w

Escape

• A symbol with a special meaning in a regular expression, which is escaped using \

Repeat

Code	Description	Example
*	The preceding regular expression repeats 0 or more times
+	The preceding regular expression repeats at least once
？	The preceding regular expression repeats 0 or 1 times
N	Repeat n times
{N,}	Repeat more than n times
{N,m}	Repeat N to M times

Grouping (capturing) assertions

Code	Description	Example
X	Y	Match x or Y
(pattern)	Group numbers are automatically assigned after grouping (capture) starting from 1 You can change the priority \ Number match corresponding grouping (refers to the contents of the group on the previous match)
(?:p Attern)	Change priority non-grouping only
(? <name>exp) (?name Exp	The group captures the naming of the Python syntax as a (? P<NAME>EXP)
(? =exp)	0 width Positive lookahead assertion assertion exp must appear on the right side of the match
(? <=exp)	0 width is recalling the post assertion assertion that exp must appear on the left side of the match
(?! Exp	0 width Negative lookahead assertion asserts that exp must not appear on the right side
(? <!exp)	0 width Negative Review post assertion asserts that Exp must not appear on the left side
(? #comment)	Comments

Assertion does not occupy a group number

Greed and non-greed

• Default greedy mode, as many matching strings as possible

Code	Description	Example
*?	Match any number of times and repeat as little as possible
+?	Match at least once and repeat as little as possible
??	Match 0 or 1 times and repeat as little as possible
{n}?	Match at least n times and repeat as little as possible
{n,m}?	Match at least N times, up to M times, as few repetitions as possible

Engine options

Code	Description	Example
IgnoreCase	Ignore case when matching	Re. Ire.ignorecase
Singleline	Single-line mode, can penetrate/n	Re. Sre.dotall
Multiline	Multi-line mode	Re. Mre.multiline
Ignorepatternwhitespace	Ignore expression whitespace character, to use white space characters	Re. Xre.verbose

Code Description Example
IgnoreCase match ignores case re. Ire.ignorecase
Singleline single-line mode, which penetrates the/n re. Sre.dotall
Multiline Multi-line mode re. Mre.multiline
Ignorepatternwhitespace ignores the expression whitespace characters to use the white-space character re. Xre.verbose

Use | (bitwise OR) operations in Python to turn on multiple options

Python Regular Expressions RE module compilation

• Re.compile (pattern, flags=0)
  • Returns the regular Expression object regex
  • The results of the regular expression compilation are saved, and the next time you use the same pattern, you do not need to recompile

One-time match

• Regex.match (string[, pos[, Endpos])

  • Match from beginning of string to specify start and end position return match object

• Regex.search (string[, pos[, Endpos])

  • Search from scratch until the first match, specifying the start and end positions to return the match object
• Regex.fullmatch (string[, pos[, Endpos])
  • Match the entire string to the regular expression

Full-Text Search

• Regex.findall (string[, pos[, Endpos])

  • Matches the entire string from left to right, returning a list of all occurrences
• Regex.finditer (string[, pos[, Endpos])
  • Matches the entire string, left-to-right, and returns all occurrences of the iterator, each of which is a match object

Match substitution

• Regex.sub (Replacement, string, count=0)

  • Use pattern to match string strings and replace matches with replacement
  • Replacement can be string, bytes, function
• Regex.subn (Replacement, string, count=0)
  • Functions like a sub return a tuple (new_string, Number_of_subs_made)

Split string

• Regex.Split (String, maxsplit=0)
  • Return to List

Group

• using (pattern) captured data to put in a group

• Match class method

• Group (N)

  • 1-n the corresponding group 0 but will match the entire string
  • If a named grouping is used, the group (name) method can be taken out

• Groups ()

  • Returns a tuple of all groups
• Groupdict ()
  • Returns a dictionary of all named groupings

Todo:argparse

Python Sixth Week Study notes (2)