Question

Python Questions：

Q1. list_1= ['wind', 'spring', 'summer', 'purse', 'great', 'sports']

Use re.search() in the re package and list comprehension to find all words in list_1 that does not contain the letter "r".

Q2.

str_1= '''I live in a room by the sea,
where the view is great and the food is free.
Some of the tenants come and go.
Some I eat, if they're too slow.
One end of me is firmly locked.
The other end just gently rocks.
I live in a room by the sea.
It's perfect for an anemone. '''
Use re.search() in the re package to find all lines that does not start with the letter "s", "S", or "I".

Q3. list_1= ['attitudes', 'ab\nchild', '2!apologies', 'echess', 'fly\n', 'cheer']
Use list comprehension and functions in re package to filter all elements that start with "ch" or end with "es".

Q4. Remove everything from the first occurrence of "e" till end of the string, using the function .sub() from the "re" package

str_1 = 'Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.'

Answer 1

Before we start coding we have to know the basics of re

.   (dot) represents any character except \n

^ represents starts with ex: '^h' will satisfy "helloworld"

$ represents  ends with ex: 'i$' will satisfy "hii"

| represents or ex: '^h|o$'  will satisfy for both "hi" and "hello"

*   Zero or more occurrences

ex: '.*' will satisfy any string

here ->

• . means one character
• * means any no of times

So ( .* ) finally represents any number of characters.

List comprehension in python :

• [ ] this symbol represents list type and here the contents placed inside these symbols directly converted to list type
• [ i for i in range(5) ] this statement generates integers from 0 to 5
• 0 1 2 3 4

Solutions

Q1

import re

list_1= ['wind', 'spring', 'summer', 'purse', 'great', 'sports']

print([i for i in list_1 if not re.search('r',i)])

[ i for i in list_1 if not re.search('r',i) ]
this statement is equivalent to

for word in list_1:

if not re.search('r',word): #if r is not found in word

print(word)

Hope you understand how list comprehension internally works!

Q2 Solution

import re

str_1= '''I live in a room by the sea,
where the view is great and the food is free.
Some of the tenants come and go.
Some I eat, if they're too slow.
One end of me is firmly locked.
The other end just gently rocks.
I live in a room by the sea.
It's perfect for an anemone. '''

print(*[line for line in str_1.split('\n') if not re.search('^S|^s|^I',line)])


#^s|^s|^I means if line starts with s or S or I
#str_1.split means total string is splitted into lines and matches with re

Q3 Solution

import re

list_1= ['attitudes', 'ab\nchild', '2!apologies', 'echess', 'fly\n', 'cheer']

print([word for word in list_1 if re.match('^ch|.*es$',word)])


#re will match word startswith ch  ^ch  | or ends with es .*es$

Q4 Solution

import re

str_1 = 'Two things are infinite: the universe and human stupidity; and I\'m not sure about the universe.'
        
print("".join([str_1[i] for i in range(re.search('e',str_1).start())]))


#start() method in re search will say the first position that e appears
#''.join will join all the characters obtained in the list comprehension
#we will traverse through str_1 and prints upto first appearance of character e 

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