PYTHON

python regex

import re

# Regex Cheat sheet : https://www.dataquest.io/blog/regex-cheatsheet/
# Regex python tester : https://pythex.org/
# re doc : https://docs.python.org/3/library/re.html

text = "i like train" 
reg = r"[a-c]" #the group of char a to c

if re.match(reg, text): #Check if regex is correct
	print(text)
else:
  print("Not any match")

python regex

# You need to - (import re)
# ^		    - Matches the beginning of the line
# $		    - Matches the end of the line
# .		    - Matches any character
# s	    - Matches whitespace
# S	    - Matches any non-whitespace character
# *		    - Repeat a character zero or more times
# *?	    - Repeat a character zero or more times (non-greedy)
# +		    - Repeat a character one or more times
# +?	    - Repeat a character one or more times (non-greedy)
# [aeiou]	- Matches a single character in the listed set
# [^XYZ]	- Matches a single character not in the listed set
# [a-z0-9]	- The set of characters can include a range
# (			- Indicates where string extraction is to start
# )			- Indicates where string extraction is to end

1. A fixed string -> abc123
2. Arbitrary repetition -> a*b ( "*" means that you can have an arbitrary
								number (possibly 0) of the previous char
3. Repeat character at least once -> a+b # ab, aaaab
4. Repeat character at most once -> a?b # b, ab
5. Repeat a character a fixed number of timers -> a{5} # aaaaa
6. Repeat a pattern a fixed number of times -> (a*b){3} # baabab, ababaaaab
7. Repeat a character or pattern a variable number of times -> a{2,4} # aa, aaa, aaaa
8. Choice of several characters -> [ab]c # ac, bc
9. Arbitrary mixture of several characters -> [ab]*c # c, aac, abbac
10. Ranges of characters -> [A-H][a-z]* # Aasdfalsd, Hb, G 
11. Characters OTHER than particular one -> [^AB] # C, D
12. Choice of several expressions -> Dr|Mr|Ms|Mrs # Dr, Mr, Mrs, Ms
13. Nesting expressions -> ([A-Z][a-z][0-9])* # A, AzSDFcvfg
14. Start of a line -> ^ab
15. End of a line -> ab$

#Type of pattern
1. Special characters -> [ # [
2. Any charactter 'except' newline -> . # a, *, -
3. Nongreedy evaluation -> <.*>? # <h1></h2 name = "foo">
4. Whitespace -> s 

python regular expression

import re

# The string you want to find a pattern within
test_string = 'Hello greppers!'

# Creating a regular expression pattern
# This is a simple one which finds "Hello"
pattern = re.compile(r'Hello')

# This locates and returns all the occurences of the pattern
# within the test_string
match = pattern.finditer(test_string)

# Outputs all the ocurrences which were returned as 
# as match objects
for match in matches:
  print(match)

python regular expressions

import re

# returns a match object if found else None
txt = "Hello world"
x = re.search(r"[a-zA-z]+", txt)

if x:
    print("YES! We have a match!", x)
else:
    print("No match")
# output YES! We have a match! <re.Match object; span=(0, 5), match='Hello'>


# returns a list of all matches found - regular express finds all vowels in this example
txt = "This is a test"
x = re.findall(r"[aeiou]", txt)
print(x)
# output ['i', 'i', 'a', 'e']


# returns a list of all matches found - regular expression find is or test in string case-insensitive
txt = "This iS a Test"
x = re.findall("(is|test)", txt, flags=re.IGNORECASE)
print(x)
# output ['is', 'iS', 'Test']

txt = "This is a silly string"
# splits a string into a list using regular expression
x = re.split(r"silly", txt)
print(x)
# output ['This is a ', ' string']


# replace concatenated tototo with to
txt = "We need tototo run "
x = re.sub(r"(to)+", "to", txt)
print(x)
# output We need to run

python regex match

# Step-By-Step breakdown:

import re  # We need this module
# First make a regex object containing your regex search pattern. Replace REGEX_GOES_HERE with your regex search. Use either of these:
regex_obj = re.compile(r'REGEX_GOES_HERE', flags=re.IGNORECASE)  # Case-insensitive search:
regex_obj = re.compile(r'REGEX_GOES_HERE')  # Case-sensitive search

# Define the string you want to search inside:
search_txt = "These are oranges and apples and pears"

# Combine the two to find your result/s:
regex_obj.findall(search_txt)

#And it wrapped in print:
print(regex_obj.findall(search_txt))  # Will return a LIST of all matches. Will return empty list on no matches.

regular expression syntax python

1. A fixed string -> abc123
2. Arbitrary repetition -> a*b ( "*" means that you can have an arbitrary
								number (possibly 0) of the previous char
3. Repeat character at least once -> a+b # ab, aaaab
4. Repeat character at most once -> a?b # b, ab
5. Repeat a character a fixed number of timers -> a{5} # aaaaa
6. Repeat a pattern a fixed number of times -> (a*b){3} # baabab, ababaaaab
7. Repeat a character or pattern a variable number of times -> a{2,4} # aa, aaa, aaaa
8. Choice of several characters -> [ab]c # ac, bc
9. Arbitrary mixture of several characters -> [ab]*c # c, aac, abbac
10. Ranges of characters -> [A-H][a-z]* # Aasdfalsd, Hb, G 
11. Characters OTHER than particular one -> [^AB] # C, D
12. Choice of several expressions -> Dr|Mr|Ms|Mrs # Dr, Mr, Mrs, Ms
13. Nesting expressions -> ([A-Z][a-z][0-9])* # A, AzSDFcvfg
14. Start of a line -> ^ab
15. End of a line -> ab$

#Type of pattern
1. Special characters -> [ # [
2. Any charactter 'except' newline -> . # a, *, -
3. Nongreedy evaluation -> <.*>? # <h1></h2 name = "foo">
4. Whitespace -> s 

regular expressions in python

# You need to - (import re)
# ^		    - Matches the beginning of the line
# $		    - Matches the end of the line
# .		    - Matches any character
# s	    - Matches whitespace
# S	    - Matches any non-whitespace character
# *		    - Repeat a character zero or more times
# *?	    - Repeat a character zero or more times (non-greedy)
# +		    - Repeat a character one or more times
# +?	    - Repeat a character one or more times (non-greedy)
# [aeiou]	- Matches a single character in the listed set
# [^XYZ]	- Matches a single character not in the listed set
# [a-z0-9]	- The set of characters can include a range
# (			- Indicates where string extraction is to start
# )			- Indicates where string extraction is to end 

regex in python

import re

text = "test1, test2, test3"
regex = re.compile(r"test1")

# Returns range of first match
print(regex.match(text).span())

# Returns text with all matches replaces with other text
print(regex.sub("replace", text))

# Returns every match
print(regex.findall(text))

# OUT:
#
# (0, 5)
# replace, replace, replace
# ['test1', 'test2', 'test3']

regex in python

'''
Regex (Regular Expression) are incredibly powerful,
and can do much more than regular text search.
'''
import re 
# a. The dot Regex, how to know how to match an arbitrary character
#                   by using the dot regex.
text = '''A blockchain, originally block chain,
is a growing list of records, called blocks,
which are linked using cryptography.
'''
print(re.findall('b...k', text)) # Output: ['block', 'block', 'block']

# b. The asterisk Regex, match text that begins and ends with the character
#                       and an arbitrary number of characters. We also can use 
#                       the asterisk operator in combination
print(re.findall('cr.*', text)) # Output: ['cryptography.']
print(re.findall('y.*y', text)) # Output: ['yptography']

# c. The Zero-or-one Regex / '?' chracter, to know how to match zero
#                         or one characters.
print(re.findall('blocks?', text)) # Output: ['block', 'block', 'blocks']

regex in python

# Let's say you want to check for a phone number in a string
# Note: Remove indentation

	import re
	phone_num_regex = re.compile(r'ddd-ddd-dddd')
	mobile_string = 'My number is 415-555-4242' # Not real number
	any_phone_numbers = phone_num_regex.search(mobile_string)
	print(any_phone_numbers)

The r in front of the string means it's a raw string (/n, /t, etc doesn't work)
In regex, if we use d, it will look for any digit in your string (0-9)

If we search for ddd-ddd-dddd, it will look for anywhere in the
string where there is a digit, followed by a digit, followed by a digit, followed
by a hyphen, ...

You can also use it in an if statement to check if there is a match or not
between a regex and a string with 're.match(regex, string)'

Python Regular Expressions

# A Python program to demonstrate working of re.match(). 
import re 
   
# Lets use a regular expression to match a date string 
# in the form of Month name followed by day number 
regex = r"([a-zA-Z]+) (d+)"
   
match = re.search(regex, "I was born on June 24") 
   
if match != None: 
   
    # We reach here when the expression "([a-zA-Z]+) (d+)" 
    # matches the date string. 
   
    # This will print [14, 21), since it matches at index 14 
    # and ends at 21. 
    print ("Match at index %s, %s" % (match.start(), match.end())) 
   
    # We us group() method to get all the matches and 
    # captured groups. The groups contain the matched values. 
    # In particular: 
    # match.group(0) always returns the fully matched string 
    # match.group(1) match.group(2), ... return the capture 
    # groups in order from left to right in the input string 
    # match.group() is equivalent to match.group(0) 
   
    # So this will print "June 24" 
    print ("Full match: %s" % (match.group(0))) 
   
    # So this will print "June" 
    print ("Month: %s" % (match.group(1))) 
   
    # So this will print "24" 
    print ("Day: %s" % (match.group(2)))
   
else: 
    print ("The regex pattern does not match.")

python regex

# Recursive Python3 program to find if a given pattern is
# present in a text
 
def exactMatch(text, pat, text_index, pat_index):
    if text_index == len(text) and pat_index != len(pat):
        return 0
  
    # Else If last character of pattern reaches
    if pat_index == len(pat):
        return 1
  
    if text[text_index] == pat[pat_index]:
        return exactMatch(text, pat, text_index+1, pat_index+1)
  
    return 0
 
  
# This function returns true if 'text' contain 'pat'
def contains(text, pat, text_index, pat_index):
    # If last character of text reaches
    if text_index == len(text):
        return 0
  
    # If current characters of pat and text match
    if text[text_index] == pat[pat_index]:
        if exactMatch(text, pat, text_index, pat_index):
            return 1
        else:
            return contains(text, pat, text_index+1, pat_index)
  
    # If current characters of pat and tex don't match
    return contains(text , pat, text_index+1, pat_index)
  
# Driver program to test the above function
 
print(contains("geeksforgeeks", "geeks", 0, 0))
print(contains("geeksforgeeks", "geeksquiz", 0, 0))
print(contains("geeksquizgeeksquiz", "quiz", 0, 0))
 
# This code is contributed by ankush_953.

Regular Expression in Python

import re
 
s = 'GeeksforGeeks: A computer science portal for geeks'
 
match = re.search(r'portal', s)
 
print('Start Index:', match.start())
print('End Index:', match.end())