My Python growth path---the fourth day---python Foundation---January 24, 2016 (icy)

Four, the regular expression    Strings are the most data structure involved in programming, and the need to manipulate strings is almost ubiquitous. For example, to determine whether a string is a legitimate email address, although it can be programmed to extract the substring before and after, and then judge whether it is a word and domain name, but this is not only cumbersome, and the code is difficult to reuse.    A regular expression is a powerful weapon used to match strings. Its design idea is to use a descriptive language to define a rule for a string, and any string that conforms to the rule, we think it "matches", otherwise the string is illegal.    The following diagram shows the process of using regular expression matching

1. Python-supported regular expression meta-characters and syntax

Grammar	Description	An instance of an expression	Full-Match string
Character
General characters	Match yourself	Abc	Abc
.	Match any character "\ n" except In Dotall mode (re. Dotall) can also match newline characters.	A.b	ABC or ABC or A1C, etc.
[...]	The character set [ABC] represents a or B or C, or it can-represent a range such as [a-d] for a or B or C or D	A[bc]c	ABC or ADC
[^...]	Non-character sets, which are characters other than []	A[^bc]c	ADC or AEC, etc.
Predefined character sets (can also be tied to character sets [...] In
\d	Number: [0-9]	A\dc	A1C, etc.
\d	Non-numeric: [^0-9] or [^\d]	A\dc	ABC, etc.
\s	White space character:[< space >\t\n\f\v]	A\sc	A B etc
\s	Non-whitespace characters: [^s]	A\sc	ABC, etc.
\w	Alpha-Numeric (word character) [a-za-z0-9]	A\wc	ABC or A1C, etc.
\w	Non-alphanumeric (non-word character) [^\w]	A\wc	A.C or A_c, etc.
Quantity words (used in characters or (...) After grouping)
*	Matches 0 or more expressions. (note including 0 times)	abc*	AB or ABCC
Boundary match (does not consume characters in the character to be matched)
^	Matches the beginning of the string, matching the beginning of each line in multiline mode	^abc	ABC or ABCD, etc.
$	Matches the end of the string, matching the end of each line in multiline mode	abc$	ABC or 123ABC etc.
\a	Match string start only	\aabc	ABC or ABCD, etc.
\z	Match string End only	Abc\z	ABC or 123ABC etc.
\b	matches a word boundary, which is the position between the word and the space. For example, ' er\b ' can match ' er ' in ' never ', but not ' er ' in ' verb '.
\b	Matches a non-word boundary. ' er\b ' can match ' er ' in ' verb ', but cannot match ' er ' in ' Never '.
Logic, grouping

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My Python growth path---the fourth day---python Foundation---January 24, 2016 (icy)