=====Problem Statement=====
The re.sub() tool (sub stands for substitution) evaluates a pattern and, for each valid match, it calls a method (or lambda).
The method is called for all matches and can be used to modify strings in different ways.
The re.sub() method returns the modified string as an output.

Learn more about re.sub().

Transformation of Strings
Code

import re

#Squaring numbers
def square(match):
    number = int(match.group(0))
    return str(number**2)

print re.sub(r"\d+", square, "1 2 3 4 5 6 7 8 9")

Output

1 4 9 16 25 36 49 64 81


Replacements in Strings

Code

import re

html = """
<head>
<title>HTML</title>
</head>
<object type="application/x-flash" 
  data="your-file.swf" 
  width="0" height="0">
  <!-- <param name="movie"  value="your-file.swf" /> -->
  <param name="quality" value="high"/>
</object>
"""

print re.sub("(<!--.*?-->)", "", html) #remove comment

Output

<head>
<title>HTML</title>
</head>
<object type="application/x-flash" 
  data="your-file.swf" 
  width="0" height="0">

  <param name="quality" value="high"/>
</object>

=====Problem Statement=====
You are given a text of N lines. The text contains && and || symbols.
Your task is to modify those symbols to the following:
&& → and
|| → or

Both && and || should have a space " " on both sides.

=====Input Format=====
The first line contains the integer, N.
The next N lines each contain a line of the text.

=====Constraints=====
0<N<100
Neither && nor || occur in the start or end of each line. 

=====Output Format=====
Output the modified text.

Difficulty: introductory

Starter code:

# Enter your code here. Read input from STDIN. Print output to STDOUT

Solutions:
import re, sys
n = int(input())
for line in sys.stdin:
    remove_and = re.sub(r'(?<= )(&&)(?= )',"and",line)
    remove_or = re.sub(r'(?<= )(\|\|)(?= )',"or",remove_and)
    print(remove_or,end='')


import re

def change(match):
    symb = match.group(0)
    
    if symb == "&&":
        return "and"
    elif symb == "||":
        return "or"
    
n = int(input().strip())
for _ in range(n):
    print(re.sub(r'(?<= )(&&|\|\|)(?= )', change, input()))