Regular expression in python for students

Introduction to regular expressions REGULAR EX P RES S ION S IN P YTH ON Maria Eugenia Inzaugarat Data Scientist

REGULAR EXPRESSIONSIN PYTHON What is a regular expression? REGular EXpression or regex: String containing a combination of normal characters and special metacharacters that describes patterns to nd text or positions within a text

REGULAR EXPRESSIONSIN PYTHON What is a regular expression? REGular EXpression or regex: String containing a combination of normal characters and special metacharacters that describes patterns to nd text or positions within a text Normal characters match themselves ( st )

REGULAR EXPRESSIONSIN PYTHON What is a regular expression? REGular EXpression or regex: String containing a combination of normal characters and special metacharacters that describes patterns to nd text or positions within a text Metacharacters represent types of characters ( d , s , w ) or ideas ( {3,10} )

REGULAR EXPRESSIONSIN PYTHON What is a regular expression? REGular EXpression or regex: String containing a combination of normal characters and special metacharacters that describes patterns to nd text or positions within a text Pattern: a sequence of characters that maps to words or punctuation

REGULAR EXPRESSIONSIN PYTHON What is a regular expression? REGular EXpression or regex: String containing a combination of normal characters and special metacharacters that describes patterns to nd text or positions within a text Pattern matching usage: Find and replace text Validate strings Very powerful and fast

REGULAR EXPRESSIONSIN PYTHON The re module import re Find all matches of a pattern: re.findall(r"#movies", "Love #movies! I had fun yesterday going to the #movies") ['#movies', '#movies']

REGULAR EXPRESSIONSIN PYTHON The re module import re Split string at each match: re.split(r"!", "Nice Place to eat! I'll come back! Excellent meat!") ['Nice Place to eat', " I'll come back", ' Excellent meat', '']

REGULAR EXPRESSIONSIN PYTHON The re module import re Replace one or many matches with a string: re.sub(r"yellow", "nice", "I have a yellow car and a yellow house in a yellow neighborhood") 'I have a nice car and a nice house in a nice neighborhood'

REGULAR EXPRESSIONSIN PYTHON Supported metacharacters re.findall(r"Userd", "The winners are: User9, UserN, User8") ['User9', 'User8'] re.findall(r"UserD", "The winners are: User9, UserN, User8") ['UserN']

REGULAR EXPRESSIONSIN PYTHON Supported metacharacters re.findall(r"Userw", "The winners are: User9, UserN, User8") ['User9', 'UserN', 'User8'] re.findall(r"Wd", "This skirt is on sale, only $5 today!") ['$5']

REGULAR EXPRESSIONSIN PYTHON Supported metacharacters re.findall(r"DatasScience", "I enjoy learning Data Science") ['Data Science'] re.sub(r"iceScream", "ice cream", "I really like ice-cream") 'I really like ice cream'

Let's practice! REGULAR EX P RES S ION S IN P YTH ON

Repetitions REGULAR EX P RES S ION S IN P YTH ON Maria Eugenia Inzaugarat Data Science

REGULAR EXPRESSIONSIN PYTHON Repeated characters Validate the following string:

REGULAR EXPRESSIONSIN PYTHON Repeated characters Validate the following string: import re password = "password1234" re.search(r"wwwwwwwwdddd", password) <_sre.SRE_Match object; span=(0, 12), match='password1234'>

REGULAR EXPRESSIONSIN PYTHON Repeated characters Validate the following string: import re password = "password1234" re.search(r"w{8}d{4}", password) <_sre.SRE_Match object; span=(0, 12), match='password1234'> Quanti ers: A metacharacter that tells the regex engine how many times to match a character immediately to its left.

REGULAR EXPRESSIONSIN PYTHON Quanti ers Once or more: + text = "Date of start: 4-3. Date of registration: 10-04." re.findall(r" ", text)

REGULAR EXPRESSIONSIN PYTHON Quanti ers Once or more: + text = "Date of start: 4-3. Date of registration: 10-04." re.findall(r"d+- ", text)

REGULAR EXPRESSIONSIN PYTHON Quanti ers Once or more: + text = "Date of start: 4-3. Date of registration: 10-04." re.findall(r"d+-d+", text) ['4-3', '10-04']

REGULAR EXPRESSIONSIN PYTHON Quanti ers Zero times or more: * my_string = "The concert was amazing! @ameli!a @joh&&n @mary90" re.findall(r"@w+W*w+", my_string) ['@ameli!a', '@joh&&n', '@mary90']

REGULAR EXPRESSIONSIN PYTHON Quanti ers Zero times or once: ? text = "The color of this image is amazing. However, the colour blue could be brighter." re.findall(r"colou?r", text) ['color', 'colour']

REGULAR EXPRESSIONSIN PYTHON Quanti ers n times at least, m times at most : {n, m} phone_number = "John: 1-966-847-3131 Michelle: 54-908-42-42424" re.findall(r" ", phone_number)

REGULAR EXPRESSIONSIN PYTHON Quanti ers n times at least, m times at most : {n, m} phone_number = "John: 1-966-847-3131 Michelle: 54-908-42-42424" re.findall(r"d{1,2}- ", phone_number)

REGULAR EXPRESSIONSIN PYTHON Quanti ers n times at least, m times at most : {n, m} phone_number = "John: 1-966-847-3131 Michelle: 54-908-42-42424" re.findall(r"d{1,2}-d{3}- ", phone_number)

REGULAR EXPRESSIONSIN PYTHON Quanti ers n times at least, m times at most : {n, m} phone_number = "John: 1-966-847-3131 Michelle: 54-908-42-42424" re.findall(r"d{1,2}-d{3}-d{2,3}-d{4,}", phone_number) ['1-966-847-3131', '54-908-42-42424']

REGULAR EXPRESSIONSIN PYTHON Quanti ers Immediately to the left r"apple+" : + applies to e and not to apple

Regex metacharacters REGULAR EX P RES S ION S IN P YTH ON Maria Eugenia Inzaugarat Data Scientist

REGULAR EXPRESSIONSIN PYTHON Looking for patterns Two different operations to nd a match: re.search(r"d{4}", "4506 people attend the show <_sre.SRE_Match object; span=(0, 4), match='4506 re.search(r"d+", "Yesterday, I saw 3 shows") <_sre.SRE_Match object; span=(17, 18), match='3'> re.match(r"d{4}", "4506 people attend the show" <_sre.SRE_Match object; span=(0, 4), match='4506 print(re.match(r"d+","Yesterday, I saw 3 shows" None

REGULAR EXPRESSIONSIN PYTHON Special characters Match any character (except newline): . my_links = "Just check out this link: www.amazingpics.com. It has amazing photos!" re.findall(r"www com", my_links)

REGULAR EXPRESSIONSIN PYTHON Special characters Match any character (except newline): . my_links = "Just check out this link: www.amazingpics.com. It has amazing photos!" re.findall(r"www.+com", my_links) ['www.amazingpics.com']

REGULAR EXPRESSIONSIN PYTHON Special characters Start of the string: ^ my_string = "the 80s music was much better that the 90s" re.findall(r"thesd+s", my_string) ['the 80s', 'the 90s'] re.findall(r"^thesd+s", my_string) ['the 80s']

REGULAR EXPRESSIONSIN PYTHON Special characters End of the string: $ my_string = "the 80s music hits were much better that the 90s" re.findall(r"thesd+s$", my_string) ['the 90s']

REGULAR EXPRESSIONSIN PYTHON Special characters Escape special characters: my_string = "I love the music of Mr.Go. However, the sound was too loud." print(re.split(r".s", my_string)) ['', 'lov', 'th', 'musi', 'o', 'Mr.Go', 'However', 'th', 'soun', 'wa', 'to', 'loud.'] print(re.split(r".s", my_string)) ['I love the music of Mr.Go', 'However, the sound was too loud.']

REGULAR EXPRESSIONSIN PYTHON OR operator Character: | my_string = "Elephants are the world's largest land animal! I would love to see an elephant one day" re.findall(r"Elephant|elephant", my_string) ['Elephant', 'elephant']

REGULAR EXPRESSIONSIN PYTHON OR operator Set of characters: [ ] my_string = "Yesterday I spent my afternoon with my friends: MaryJohn2 Clary3" re.findall(r"[a-zA-Z]+d", my_string) ['MaryJohn2', 'Clary3']

REGULAR EXPRESSIONSIN PYTHON OR operator Set of characters: [ ] my_string = "My&name&is#John Smith. I%live$in#London." re.sub(r"[#$%&]", " ", my_string) 'My name is John Smith. I live in London.'

REGULAR EXPRESSIONSIN PYTHON OR operand Set of characters: [ ] ^ transforms the expression to negative my_links = "Bad website: www.99.com. Favorite site: www.hola.com" re.findall(r"www[^0-9]+com", my_links) ['www.hola.com']

Greedy vs. non- greedy matching REGULAR EX P RES S ION S IN P YTH ON Maria Eugenia Inzaugarat Data Scientist

REGULAR EXPRESSIONSIN PYTHON Greedy vs. non-greedy matching Two types of matching methods: Greedy Non-greedy or lazy Standard quanti ers are greedy by default: * , + , ? , {num, num}

REGULAR EXPRESSIONSIN PYTHON Greedy matching Greedy: match as many characters as possible Return the longest match import re re.match(r"d+", "12345bcada") <_sre.SRE_Match object; span=(0, 5), match='12345'>

REGULAR EXPRESSIONSIN PYTHON Greedy matching Backtracks when too many character matched Gives up characters one at a time import re re.match(r".*hello", "xhelloxxxxxx") <_sre.SRE_Match object; span=(0, 6), match='xhello'>

REGULAR EXPRESSIONSIN PYTHON Non-greedy matching Lazy: match as few characters as needed Returns the shortest match Append ? to greedy quanti ers import re re.match(r"d+?", "12345bcada") <_sre.SRE_Match object; span=(0, 1), match='1'>

REGULAR EXPRESSIONSIN PYTHON Non-greedy matching Backtracks when too few characters matched Expands characters one a time import re re.match(r".*?hello", "xhelloxxxxxx") <_sre.SRE_Match object; span=(0, 6), match='xhello'>

Regular expression in python for students

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