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String in Python


You have already been introduced with strings.
a = "Hey there"
Like list, string is also a collection. They are collection of characters.

  • Python 2
  • Python 3
a = "Hey there"
print a[1]
a = "Hey there"
print(a[1])
Output
e

Like list, we can also use 'len' and 'slice' on a string.

  • Python 2
  • Python 3
a = "Hello World"
print len(a)
print a[1:4]
a = "Hello World"
print(len(a))
print(a[1:4])
Output
11
ell

But unlike lists, strings are immutable. This means that we that we can't change any element of a string. So, we can't do a[2]='b' as we did with lists. Let's see what happens when we try to write this.

  • Python 2
  • Python 3
a =  "Hello World!"
a[2] = 'b'
a =  "Hello World!"
a[2] = 'b'
Output
a[2] = 'b'
TypeError: 'str' object does not support item assignment

You got this error because you can't change any element of a string.

We can also use for loop on strings. for loop will be discussed in a later chapter.

Splitting a Stirng


  • Python 2
  • Python 3
import string
a = "Hey there world"
print a.split()
import string
a = "Hey there world"
print(a.split())
Output
['Hey', 'there', 'world']

import string - We are making use of Python's string directory. It contains many useful functions. See more at Python's official documentation.

split function splits a string when it encounters a space(" ") and put them into a list.

To split at a particular place.

We can also use the split function to split a string with something other than a 'space'. Let's see how:

  • Python 2
  • Python 3
import string
a = "Buggy bug buggy bug, where are you my buggy bug!"
print a.split('b')
import string
a = "Buggy bug buggy bug, where are you my buggy bug!"
print(a.split('b'))
Output
['Buggy ', 'ug ', 'uggy ', 'ug, where are you my ', 'uggy ', 'ug!']

Here we wanted our string to split at 'b'. So, we passed 'b' to the 'split()' function and it's done.

String Comparison


Comparison of strings in Python is very simple. We just use '==', '<,' ,'>' ,'>=' , '<=' operators. Let's see an example:

  • Python 2
  • Python 3
a = raw_input()
if a>"abc":
	print 'your word comes after abc'
elif a<"abc":
	print 'your word comes before abc'
else:
	print 'your word is abc'
a = input()
if a>"abc":
	print('your word comes after abc')
elif a<"abc":
	print('your word comes before abc')
else:
	print('your word is abc')
Output
as
your word comes after abc
Python does not handle uppercase and lowercase letters the same way that people do. All the uppercase letters come before all the lowercase letters.

See this example of taking a string input of numbers which are separated by a space and storing them in a list as ints.

  • Python 2
  • Python 3
a = raw_input()
b = a.split()
print b
c = map(int,b)
print c
a = input()
b = a.split()
print(b)
c = list(map(int,b))
print(c)
Output
1 2 3 4 5 6 7 8 9
['1', '2', '3', '4', '5', '6', '7', '8', '9']
[1, 2, 3, 4, 5, 6, 7, 8, 9]

We first split the string using the 'split' function and stored them into a list. And then the'map' function changed all the strings of the list to integers.

Useful String Functions


Let's have a look at some useful functions which we can use on a list.

capitalize


Capitalizes the first character of a string

  • Python 2
  • Python 3
import string
a = "hey there world!"
print a.capitalize()
print a
import string
a = "hey there world!"
print(a.capitalize())
print(a)
Output
Hey there world!

lower


Turns every character of the string into lower case.

  • Python 2
  • Python 3
import string
a = "hEy tHEre WOrld!"
print a.lower()
import string
a = "hEy tHEre WOrld!"
print(a.lower())
Output
hey there world!

upper


Turns every character of the string into upper case.

  • Python 2
  • Python 3
import string
a = "hEy tHEre WOrld!"
print a.upper()
import string
a = "hEy tHEre WOrld!"
print(a.upper())
Output
HEY THERE WORLD!

join


Joins the element of a list to form a string. It will be clear by the example given below.

  • Python 2
  • Python 3
import string
a = ["hEy", "tHEre", "WOrld!"]
print " ".join(a)
print ";".join(a)
import string
a = ["hEy", "tHEre", "WOrld!"]
print(" ".join(a))
print(";".join(a))
Output
hEy tHEre WOrld!
hEy;tHEre;WOrld!

swapcase


Inverts the case of a string

  • Python 2
  • Python 3
import string
a = "hEy tHEre WOrld!"
print a.swapcase()
import string
a = "hEy tHEre WOrld!"
print(a.swapcase())
Output
HeY TheRE woRLD!

You have seen many useful things to do with string in this chapter. But there are a lot more functions to explore. You can use them whenever you need them from the official documentation.

If you don't practice, you don't deserve to win.
- Andre Agassi


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