RegularExpression.py

import re

txt = "The rain in Spain"
x = re.search("^The.*Spain$", txt)

str = "The rain in Spain"
x = re.findall("ai", str)
print(x)


str = "The rain in Spain"
x = re.search("\s", str)

print("The first white-space character is located in position:", x.start())

str = "The rain in Spain"
x = re.split("\s", str, 1)
print(x)



fh = open(r"test_emails.txt", "r").read()
import re

for line in re.findall("From:.*", fh):
    print(line)


match = re.findall("From:.*", fh)

for line in match:
    print(re.findall("wS*@.*w", line))

match = re.search("From:.*", fh)
print(type(match))
print(type(match.group()))
print(match)
print(match.group())

'''
findall Returns a list containing all matches
search  Returns a Match object if there is a match anywhere in the string
split Returns a list where the string has been split at each match
sub Replaces one or many matches with a string


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


\A  Returns a match if the specified characters are at the beginning of the string  "\AThe" 
\b  Returns a match where the specified characters are at the beginning or at the end of a word r"\bain"
r"ain\b"  
\B  Returns a match where the specified characters are present, but NOT at the beginning (or at the end) of a word  r"\Bain"
r"ain\B"  
\d  Returns a match where the string contains digits (numbers from 0-9) "\d"  
\D  Returns a match where the string DOES NOT contain digits  "\D"  
\s  Returns a match where the string contains a white space character "\s"  
\S  Returns a match where the string DOES NOT contain a white space character "\S"  
\w  Returns a match where the string contains any word characters (characters from a to Z, digits from 0-9, and the underscore _ character) "\w"  
\W  Returns a match where the string DOES NOT contain any word characters "\W"  
\Z  Returns a match if the specified characters are at the end of the string  "Spain\Z"


[arn] Returns a match where one of the specified characters (a, r, or n) are present  
[a-n] Returns a match for any lower case character, alphabetically between a and n  
[^arn]  Returns a match for any character EXCEPT a, r, and n  
[0123]  Returns a match where any of the specified digits (0, 1, 2, or 3) are present 
[0-9] Returns a match for any digit between 0 and 9 
[0-5][0-9]  Returns a match for any two-digit numbers from 00 and 59  
[a-zA-Z]  Returns a match for any character alphabetically between a and z, lower case OR upper case  
[+] In sets, +, *, ., |, (), $,{} has no special meaning, so [+] means: return a match for any + character in the string


'''