Python_Regular Expression

Programming with Sikander CorporateTrainer: C, Modern C++, Python, Linux System Prog

Programming with Sikander : Python: Regular Expression  Regular expressions are a powerful tool for various kinds of string manipulation.  They are a domain specific language (DSL) that is present as a library in most modern programming languages, not just Python.  They are useful for two main tasks:  identify whether a pattern exists in a given sequence of characters (string) or not.  performing substitutions in a string.

Programming with Sikander : Python: Regular Expression  Implemented in Python with the “re” module  import re

Programming with Sikander : Python: Regular Expression  re.match  re.search  re.findall  re.finditer  re.fullmatch

Programming with Sikander : Python: Regular Expression  re.match function can be used to determine whether pattern matches at the beginning of a string.  If it does, match returns an object representing the match, if not, it returns None.  re.match(pattern, sequence)

Programming with Sikander : Python: Regular Expression

Programming with Sikander : Python: Regular Expression  The function re.search finds a match of a pattern anywhere in the string.

Programming with Sikander : Python: Regular Expression  The search function returns an object with several methods that give details about it. These methods include  group which returns the string matched.  start and end which return the start and ending positions of the first match  span which returns the start and end positions of the first match as a tuple.

Programming with Sikander : Python: Regular Expression  The function re.findall returns a list of all substrings that match a pattern.

Programming with Sikander : Python: Regular Expression  re.finditer(pattern, string)  Return an iterator yielding match objects over all non-overlapping matches for the pattern in string.  The string is scanned left-to-right, and matches are returned in the order found.

Programming with Sikander : Python: Regular Expression Example Description Character "[a-m]" A set of characters [] "d" Signals a special sequence (can also be used to escape special characters) "he..o" Any character (except newline character) . "^hello" Starts with ^ "world$" Ends with $ "aix*" Zero or more occurrences * "aix+" One or more occurrences + "al{2}" Excactly the specified number of occurrences {} "falls|stays" Either or | Capture and group ()

Programming with Sikander : Python: Regular Expression Print all the vowels and its index Input : sikander Output : 1 i 3 a 6 e

Programming with Sikander : Python: Regular Expression Matches any decimal digit; this is equivalent to the class [0-9]. d Matches any non-digit character; this is equivalent to the class [^0-9]. D Matches any whitespace character; this is equivalent to the class [ tnr]. s Matches any non-whitespace character; this is equivalent to the class [^ tnr]. S Matches any alphanumeric character; this is equivalent to the class [a- zA-Z0-9_]. w Matches any non-alphanumeric character; this is equivalent to the class [^a-zA-Z0-9_]. W

Programming with Sikander : Python: Regular Expression  The expression d matches any digit [0-9]  The expression D matches any character that is not a digit.  Given a String extract All the digits and non-digits. Output Input Digits : 1 0 2 0 2 3 Non Digits : R V E C 1RV02EC023 Digits : 1 2 3 4 Non Digits : A B C D E F ABCDE1234F Digits : 2 0 0 0 Non Digits : R u p e e s Rupees 2000

Programming with Sikander : Python: Regular Expression • s matches any whitespace character [ tnr] • S matches any non-white space character.  Given a String extract all spaces and Non space characters.

Programming with Sikander : Python: Regular Expression • The expression w will match any word character. • Word characters include alphanumeric characters (a-z,A-Z, 0-9) and underscore(_) • Given a string, extract all word and non-word characters (remove all special characters)

Programming with Sikander : Python: Regular Expression  The ^ symbol matches the position at the start of a string.  The $ symbol matches the position at the end of a string.

Programming with Sikander : Python: Regular Expression • One or more occurrences(+) of digits

Programming with Sikander : Python: Regular Expression • You are given a list of phone numbers and you are required to check whether they are valid mobile numbers. • A valid mobile number is a ten digit number starting with a 7, 8 or 9.

Programming with Sikander : Python: Regular Expression • Verify if the given PAN number is correct. • PAN Number:  It’s a 10 letter string  First 5 characters are alphabets  Next 4 characters are digits  Last character is alphabet

Programming with Sikander : Python: Regular Expression Verify if the given USN number is correct.

Programming with Sikander : Python: Regular Expression • Pattern = “word1|word2|word3” • Verify if the sequence contains “from” or “to”

Programming with Sikander : Python: Regular Expression A group() expression returns one or more subgroups of the match. A groups() expression returns a tuple containing all the subgroups of the match.

Programming with Sikander : Python: Regular Expression  Given an email-id seperate the username, website and extension

Programming with Sikander : Python: Regular Expression A groupdict() expression returns a dictionary containing all the named subgroups of the match, keyed by the subgroup name.

Programming with Sikander : Python: Regular Expression  re.sub (pattern, repl, string)  Returns the string obtained by replacing the pattern in string by the replacement repl.

Programming with Sikander : Python: Regular Expression Bangalore is the capital of Karnataka. The Silicon City of India is Bangalore. Bangalore was called garden city because of its greenary. Task: Replace all the occurance of Bangalore to Bengaluru.

Programming with Sikander : Python: Regular Expression  re.compile(pattern, flags=0)  Compile a regular expression pattern into a regular expression object, which can be used for matching using its match(), search() and other methods.  It also helps to search a pattern again without rewriting it.

Python_Regular Expression

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