![Regular Expressions Quick Guide
+ Repeats a character one or more times
+? Repeats a character one or more times (non-greedy)
[aeiou] Matches a single character in the listed set
( Indicates where string extraction is to start
) Indicates where string extraction is to end
[^XYZ] Matches a single character not in the listed set
[a-z0-9] The set of characters can include a range
backslash (or escape character) quotes the character after it, both
special and ordinary.](https://image.slidesharecdn.com/regularexpressions-220505150118/85/Regular_Expressions-pptx-4-320.jpg)
![The Regular Expression Module
• Before you can use regular expressions in your program,
you must import the library using "import re"
• You can use re.search() to see if a string matches a regular
expression similar to using the find() method for strings
• You can use re.findall() extract portions of a string that
match your regular expression similar to a combination of
find() and slicing: var[5:10]](https://image.slidesharecdn.com/regularexpressions-220505150118/85/Regular_Expressions-pptx-8-320.jpg)
![Matching & Extracting Data
• The re.search() returns a True/False depending on whether
the string matches the regular expression
• If we want the matching strings to be extracted, we use
re.findall()
>>> import re
>>> x = 'My 2 favorite numbers are 19 and 42'
>>> y = re.findall('[0-9]+',x)
>>> print y
['2', '19', '42']
[0-9]+
One or more digits](https://image.slidesharecdn.com/regularexpressions-220505150118/85/Regular_Expressions-pptx-11-320.jpg)
Regular_Expressions.pptx
- 1. © Copyright 2020. All rights reserved. Regular Expressions
- 2. REGULAR EXPRESSIONS In computing, a regular expression, also referred to as "regex" or "regexp", provides a concise and flexible means for matching strings of text, such as particular characters, words, or patterns of characters. A regular expression is written in a formal language that can be interpreted by a regular expression processor.
- 3. Regular Expressions Quick Guide ^ Matches the beginning of a line $ Matches the end of the line . Matches any character s Matches whitespace S Matches any non-whitespace character * Repeats a character zero or more times *? Repeats a character zero or more times (non-greedy)
- 4. Regular Expressions Quick Guide + Repeats a character one or more times +? Repeats a character one or more times (non-greedy) [aeiou] Matches a single character in the listed set ( Indicates where string extraction is to start ) Indicates where string extraction is to end [^XYZ] Matches a single character not in the listed set [a-z0-9] The set of characters can include a range backslash (or escape character) quotes the character after it, both special and ordinary.
- 5. Regular Expressions Quick Guide $ The dollar sign at the end of a regular expression signifies the end of a line, and, therefore, any character immediately before it must be located at the end of the string. d Digit D Non-Digit w word W not word
- 6. Example in java Pattern p = Pattern.compile("colou?r"); Matcher m = p.matcher("The color green"); m.find(); // returns true m.start(); // returns 4 m.end(); // returns 9 m = p.matcher("abc"); m.find(); // returns false
- 7. Example in Python # Python p = re.compile("colou?r") m = p.search("The color green") m.start() # returns 4 m = p.search("abc") # returns None
- 8. The Regular Expression Module • Before you can use regular expressions in your program, you must import the library using "import re" • You can use re.search() to see if a string matches a regular expression similar to using the find() method for strings • You can use re.findall() extract portions of a string that match your regular expression similar to a combination of find() and slicing: var[5:10]
- 9. Wild Card Characters • The dot character matches any character • If you add the asterisk character, the character is "any number of times" X-Sieve: CMU Sieve 2.3 X-DSPAM-Result: Innocent X-DSPAM-Confidence: 0.8475 X-Content-Type-Message-Body: text/plain ^X.*:
- 10. Wild Card Characters • The dot character matches any character • If you add the asterisk character, the character is "any number of times" X-Sieve: CMU Sieve 2.3 X-DSPAM-Result: Innocent X-DSPAM-Confidence: 0.8475 X-Content-Type-Message-Body: text/plain ^X.*: Match the start of the line Many times Match any character
- 11. Matching & Extracting Data • The re.search() returns a True/False depending on whether the string matches the regular expression • If we want the matching strings to be extracted, we use re.findall() >>> import re >>> x = 'My 2 favorite numbers are 19 and 42' >>> y = re.findall('[0-9]+',x) >>> print y ['2', '19', '42'] [0-9]+ One or more digits
- 12. Re.match vs re.search There is a difference between the use of both functions. Both return the first match of a substring found in the string, but re.match() searches only from the beginning of the string and return match object if found. But if a match of substring is found somewhere in the middle of the string, it returns none. While re.search() searches for the whole string even if the string contains multi-lines and tries to find a match of the substring in all the lines of string.
- 14. References • Regular expression tester: https://regex101.com/ • URLs to refer: https://www.regular-expressions.info/modifiers.html https://docs.python.org/3.6/library/re.html#re.I http://evc-cit.info/comsc020/python-regex-tutorial/ https://www.w3schools.com/jsref/jsref_obj_regexp.asp • Regex questions with solution (Pre-requisite: Anaconda must be installed in your machine to run jupyter notebook): • Other important documents to refer: Regex Notes Regex cheatsheet
- 15. © Copyright 2021. All rights reserved. THANK YOU