Regular Expression Exercise in python

1. Write a Python program that matches a string that has an a followed by zero or more b's
   

   
   import re
   str_check=raw_input("Enter a string")
   match=re.search(r'ab*',str_check)
   if match:
       print("Matched string is",match.group())
   else:
       print("string didn't match")
   
   

   
   Enter a string abby
   ('Matched string is', 'abb')
   Enter a string a
   ('Matched string is', 'a')
   Enter a string b
   string didn't match
   



2. Write a Python program that matches a string that has an a followed by one or more b's
   

   
   import re
   str_check=raw_input("Enter a string")
   match=re.search(r'ab+',str_check)
   if match:
       print("Matched string is",match.group())
   else:
       print("string didn't match")
   
   

   
   Enter a string abby
   ('Matched string is', 'abb')
   Enter a string a
   string did'nt match
   Enter a string b
   string didn't match
   

3. Write a Python program that matches a string that has an a followed by zero or one 'b'
   

   
   import re
   str_check=raw_input("Enter a string")
   match=re.search(r'ab?',str_check)
   if match:
       print("Matched string is",match.group())
   else:
       print("string didn't match")
   
   

   
   Enter a string abbbbby
   ('Matched string is', 'ab')
   Enter a string a
   ('Matched string is', 'a')
   Enter a string b
   string didn't match
   

4. Write a Python program that matches a string that has an a followed by three 'b'.

   
   import re
   str_check=raw_input("Enter a string")
   match=re.search(r'ab{3}',str_check)
   if match:
       print("Matched string is",match.group())
   else:
       print("string didn't match")
   
   

   
   Enter a string abbbby
   ('Matched string is', 'abbb')
   Enter a string abb
   string did'nt match
   Enter a string bbb
   string didn't match
   



5. Write a Python program that matches a string that has an a followed by two to three 'b'

   
   import re
   str_check=raw_input("Enter a string")
   match=re.search(r'ab{2,3}',str_check)
   if match:
       print("Matched string is",match.group())
   else:
       print("string didn't match")
   
   

   
   Enter a string abby
   ('Matched string is', 'abb')
   Enter a string abbbbby
   ('Matched string is', 'abbb')
   Enter a string ab
   string didn't match
   



6. Write a Python program to find sequences of lowercase letters joined with a underscore

   
   import re
   str_check=raw_input("Enter a string")
   match=re.search(r'[a-z]+_[a-z]+',str_check)
   if match:
       print("Matched string is",match.group())
   else:
       print("string didn't match")
   
   

   
   Enter a string alex_lion
   ('Matched string is', 'alex_lion')
   Enter a string abbbbby
   string didn't match
   



7. Write a Python program to find sequences of one upper case letter followed by lower case letters

   
   import re
   str_check=raw_input("Enter a string")
   match=re.search(r'[A-Z]{1}[a-z]+',str_check)
   if match:
       print("Matched string is",match.group())
   else:
       print("string didn't match")
   
   

   
   Enter a string Alex_lion
   ('Matched string is', 'Alex')
   Enter a string alexTheLion
   ('Matched string is', 'The')
   



8. Write a Python program that matches a string that has an 'a' followed by anything, ending in 'b'

   
   import re
   str_check=raw_input("Enter a string")
   match=re.search(r'a.+b$',str_check)
   if match:
       print("Matched string is",match.group())
   else:
       print("string didn't match")
   
   

   
   Enter a string theappleb
   ('Matched string is', 'appleb')
   Enter a string ab
   string didn't match
   



9. Write a Python program that matches a word containing 'z', not start or end of the word