add doc

Author: heysushil

regex.py

@@ -1,4 +1,24 @@
 # regex using module re to match patterns
+
+'''
+MetaCharacters
+Metacharacters are characters that are interpreted in a special way by a RegEx engine. Here's a list of metacharacters:
+
+[] . ^ $ * + ? {} () \ |
+
+Here, [abc] will match if the string you are trying to match contains any of the a, b or c.
+
+You can also specify a range of characters using - inside square brackets.
+
+[a-e] is the same as [abcde].
+[1-4] is the same as [1234].
+[0-39] is the same as [01239].
+
+You can complement (invert) the character set by using caret ^ symbol at the start of a square-bracket.
+
+[^abc] means any character except a or b or c.
+[^0-9] means any non-digit character.
+'''
 import re
 pattern = '^a...s$'
 test_string = 'abyss'
@@ -7,4 +27,4 @@
 if result:
     print('Pattern matched')
 else:
-    print('Pattern not matched')
+    print('Pattern not matched')