What are Strings?

• Strings are the data structures which store a sequence of characters.

• Strings are immutable i.e. they cannot be changed.

• Ex: "Hello"

• "Hello" is a string of characters with characters 'h', 'e', 'l', 'l', and 'o' in it.

• A string can be initialised by single quotes and double quotes. It throws an array if used in combinations of single quotes and double quotes.

• Initialise a string.
  

  >>> s = 'abcde'
  >>> s   #Prints the output
  'abcde'
  

• The indexing on a string starts with 0 from the start and -1 from the end.

• Accessing a particular index in a string.
  

  >>> s = 'Hello'
  >>> s[2]
  l
  >>> s[-4]
  e
  

• Concatenation in a string.
  

  >>> a = "Python"
  >>> b = "3.7"
  >>> a + " " + b
  "Python 3.7"
  

• Slicing in a string is done with the help of square brackets.

• s[start:stop:step]
  

  >>> s = 'Pythonist'
  >>> s[2:4]
  th
  

Helper Functions in strings

• string.capitalize()

  Returns a copy of a string with the first letter capitalised.
  

  >>> s.capitalize()
  'Abcde'
  
  

• string.lower()

  Return a copy of a string with all the characters in lowercase.
  

  >>> a = 'Hello WORLD'
  >>> a.lower()
  hello world
  

• string.upper()

  Return a copy of a string with all the characters in lowercase.
  

  >>> a.upper()
  HELLO WORLD   
  

• string.split()

  Returns a list with the space-separated elements.
  

  >>> a.split()
  ["Hello", "World"]
  

• string.join()

  Returns a string by joining the entire set of characters in a list or a tuple.
  

  >>> l1 = ['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd']
  >>> ''.join(l1)
  'Hello World'
  

• string.swapcase()

  Returns a copy of string but with lowercase letters to uppercase and vice versa.
  

  >>> a = 'Python'
  >>> a.swapcase()
  'pYTHON'
  

• string.casefold()

  Return a copy of a string with all the characters in lowercase. It is the same as the string.lower()
  

  >>> a = 'Hello WORLD'
  >>> a.casefold()
  hello world
  

• string.center(width, fill_char)

  Returns a copy of the string in the centre with added spaces to the right and left. It takes space as a fill character if nothing is given.
  

  >>> s = 'HELLO'
  >>> s.center(30, '-')
  '------------HELLO-------------'
  
  

• string.count(string)

  Returns an integer value stating the number of occurrences of a string in a string.
  

  >>> s = 'HELLO'
  >>> s.count('L')    
  2
  

• string.endswith(string)

  Returns True if the string end with the specified string.
  

  >>> s = 'Python'
  >>> s.endswith("on")
  True
  

• string.index(string)

  Returns the index of the first occurrence in a string.
  

  >>> s = 'Hello World'
  >>> s.index('o')
  4
  

• string.isalnum()

  Returns True if all characters in the string are alphanumeric.
  

  >>> s = 'AabcD123'
  >>> s.isalnum()
  True    
  

• string.isalpha()

  Returns True if all characters in the string are in the alphabet.
  

  >>> s = 'abcd'
  >>> s.isalpha()
  True
  

• string.isdecimal()

  Returns True if all characters in the string are decimals.
  

  >>> s = '1234'
  >>> s.isdecimal()
  True
  

• string.isdigit()

  Returns True if all characters in the string are digits.
  

  >>> s = '1234'
  >>> s.isdecimal()
  True    
  

• string.islower()

  Returns True if all characters in the string are lowercase.
  

  >>> s = 'abcd'
  >>> s.islower()
  True    
  

• string.isupper()

  Returns True if all characters in the string are uppercase.
  

  >>> s = 'ABCD'
  >>> s.isupper()
  True    
  

References

• To know more about the helper functions in a string, click on the below link.

  String Methods