Regular Expressions in Python

Regular Expressions: 

 A regular expression (or RE) specifies a set of strings that matches it; the functions in this module let you check if a particular string matches a given regular expression.

 Regular expressions can contain both special and ordinary characters.

 Ordinary Characters:

Most ordinary characters, like 'A', 'a', or '0', are the simplest regular expressions; they simply match themselves.

 Special Characters:

 Some characters, like '|' or '(', are special. Special characters either stand for classes of ordinary characters or affect how the regular expressions around them are interpreted.

 The special characters are::

a)   ' . '(Dot):  this matches any character except a newline

 b)  '^': (Caret.) Matches the start of the string

 c) '$': Matches the end of the string or just before the newline at the end of the string

 d)  '*': It causes the resulting RE to match 0 or more repetitions of the preceding RE, as many repetitions as are possible. ab* will match ‘a’, ‘ab’, or ‘a’ followed by any number of ‘b’s.

 e) {m}: Specifies that exactly m copies of the previous RE should be matched; fewer matches cause the entire RE not to match. For example, a{6} will match exactly six 'a' characters, but not five.

f) 

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