Use raw string to escape backslash character in case there is Escape Sequence.
Example: “c:\yaser\now\rule” ‘\n’ and ‘\r’ will be consider as Escape Sequence. when using r"c:\yaser\now\rule" it will be escaped and the python representation will add extra backslash before each backslash. if you want to escape special character in regex don’t forgot to escape them.
r'[ab]' means a or b
r'' same as this range r'[0-9]'. ASCII Table
r'[a-zA-Z]' means any small letters or capital letters.
r'[^0-9]' means any character that is not a digit.
r'^y' means start of the string with character y. start of the string not the start of words in the string.
r’r$' means end of the string with character r.
r'^y$' means just single character y
r'.' means any single character except newline character.
r'a*'it will look at the expression, for example a character, before it and will match that 0 or more times.
r'a*'match empty string, a or aaaaa.
r'.*'match empty character, y or abcd.
r'[0-9]*'match empty character, 4 or 2131.
r'^[0-9][0-9]*$'Exclude empty character. There should be one digit and maybe there would be digits after it.
r'+' same as
r'*', but it will match 1 or more times.
r'^[0-9][0-9]*$'same as r'^[0-9]+$'
r'?' same as
r'*', but it will match 0 or 1 time.
It will return object if there is result otherwise it will be None