The regular expression of Python

1)

Match multiple regular expressions with pipe symbol (|)

Example

at | Home match at, home

2)

Match any single character (.)

Example

F.O matches any character in the middle of "F" and "o", such as FAO, F9O, F#O, etc.

3)

Match from beginning or end of character wear or word boundary (^/$/\b\b)

\b Matching pattern is a word boundary, the corresponding pattern must be at the beginning of a word;

\b Matches only the pattern that appears in the middle of a word, the character that is not on the boundary of a word.

Example

^from matches any string starting with from

/bin/tcsh$ matches any string ending with/bin/tcsh

^subject:hi$ matches a string consisting only of Subject:hi

Any string containing the "the"

\bthe any string starting with "the"

\bthe\b matches only the word "the"

4) Create character class ([])

A regular expression that uses square brackets matches any one of the characters in the square brackets.

Square brackets are only logical or functional.

Example:

B[aeiu]t Match string bat, bet, bit, but

[CR] [23] [DP] [O2] Match string has 16 combinations, first [CR] Select one, then [23] Select one, ..., and finally [O2] choose one.

5) Specify range (-) and negation (^)

A hyphen (-) in the middle of a pair of symbols in square brackets is used to denote a range of characters. such as [0-9], match the decimal number

The first character after the left parenthesis is the up arrow symbol (^), which indicates that any character in the character set is not matched. such as [^aeiou], match a non-vowel character

6) Use the closure operator (*, +,? {}) implements multiple occurrences/repeat matches

*: Match it to the left of the regular expression appears 0 or more times 0 times;

+: Matches at least one occurrence of the regular expression on its left;

?: Match it to the left of the regular expression pattern appears 0 or one time.

{}: If {m} represents a match for m occurrences, {m,n} indicates a match of M to N occurrences.

[Dn]ot? The match has a maximum of one character "T", i.e. do, no, dot, not.

[0-9] {15, 16} matches 15 or 16 digits, such as credit card number

</? [^>]+> matches all valid HTML tag strings, i.e. <...>, </...>.

7) Special characters

Some special characters can be used to represent the character set.

\d: expression [0-9]

\w: means [a-za-z0-9]

\s: denotes whitespace characters

\d: A character that represents a non-decimal number, that is, [^0-9]

Example:

\w+-\d+ represents a string of letters and numbers and at least one number, for example: ABCD-9

\D{3}-\D{3}-\D{4} such as 800-555-1212

\[email protected]\w+\.com for example [email protected]

8) Use parentheses (()) to assemble the group

Not only do we want to know if the entire string matches the regular expression, but also want to remove a particular string or substring when the match succeeds.

() function:

Grouping regular Expressions

Matching subgroups

Example:

m = Re.match (' (A (b)) ', ' AB ') two sub-groups

M.group () All matching parts

M.group (1) Matched sub-group 1 output ' AB '

M.group (2) Matched sub-group 2 output ' B '

M.groups () tuple output of all matched subgroups (' AB ', ' B ')

The regular expression of Python