Regular Expressions in Python

Question 1

r’st\d\s\w\n{3,10}’

Answer 1

r: raw
st: string
d: digit
s: white space
S:non-white space
w:word
W:non-word
n: new line

Question 2

Search the string to see if it starts with “The” and ends with “Spain”:

Answer 2

txt = “The rain in Spain”
x = re.search(“^The.*Spain$”, txt)

Question 3

Print a list of all matches with “ai”

Answer 3

txt = “The rain in Spain”
x = re.findall(“ai”, txt)
print(x)

Question 4

Search for the first white-space character in the string:

Answer 4

txt = “The rain in Spain”
x = re.search(“\s”, txt)

print(“The first white-space character is located in position:”, x.start())

returns: The first white-space character is located in position: 3

Question 5

Split at each white-space character:

txt = “The rain in Spain”

Answer 5

x = re.split(“\s”, txt)
print(x)

returns: [‘The’, ‘rain’, ‘in’, ‘Spain’]

Question 6

Split the string only at the first occurrence:

txt = “The rain in Spain”

Answer 6

x = re.split(“\s”, txt, 1)
print(x)

returns: [‘The’, ‘rain in Spain’]

Question 7

Replace every white-space character with the number 9:
txt = “The rain in Spain”

Answer 7

x = re.sub(“\s”, “9”, txt)
print(x)

returns: The9rain9in9Spain

Question 8

RegEx Functions (4)

Answer 8

findall, search, split, sub

Question 9

findall

Answer 9

Returns a list containing all matches

Question 10

search

Answer 10

Returns a Match object if there is a match anywhere in the string

Question 11

split

Answer 11

Returns a list where the string has been split at each match

Question 12

sub

Answer 12

Replaces one or many matches with a string

Question 13

Extract the substring from the 12th to the 30th character from the variable movie which corresponds to the movie title. Store it in the variable movie_title.
Get the palindrome by reversing the string contained in movie_title.
Complete the code to print out the movie_title if it is a palindrome.

Answer 13

movie_title = movie[11:30]

– Obtain the palindrome

palindrome = movie_title[::-1]

– Print the word if it’s a palindrome

if movie_title == palindrome:
print(movie_title)

Question 14

Convert the string in the variable movie to lowercase. Print the result.

Answer 14

movie_lower = movie.lower()

Question 15

Remove the $ that occur at the start and at the end of the string contained in movie_lower. Print the results.

Answer 15

movie_no_sign = movie_lower.strip(“$”)

Question 16

Split the string contained in movie_no_sign into as many substrings as possible. Print the results.

Answer 16

movie_split = movie_no_sign.split()

Question 17

To get the root of the second word contained in movie_split, select all the characters except the last one.

Answer 17

word_root = movie_split[1][:-1]

Question 18

Remove tag <\i> from the end of the string. Print the results.

Answer 18

movie_tag = movie.strip()

Question 19

Split the string contained in movie_tag using the commas as a separating element. Print the results.

Answer 19

movie_no_comma = movie_tag.split(“,”)

Question 20

Join back together the list of substring contained in movie_no_comma using a space as a join element. Print the results.

Answer 20

movie_join = “ “.join(movie_no_comma)

Question 21

Split the string file into many substrings at line boundaries.
Print out the resulting variable file_split.
Complete the for-loop to split the strings into many substrings using commas as a separator element.

Answer 21

– Split string at line boundaries
file_split = file.splitlines()

– Print file_split
print(file_split)

– Complete for-loop to split by commas

for substring in file_split:
substring_split = substring.split(“,”)
print(substring_split)

Question 22

Find if the substring actor occurs between the characters with index 37 and 41 inclusive. If it is not detected, print the statement Word not found.
Replace actor actor with the substring actor if actor occurs only two repeated times.
Replace actor actor actor with the substring actor if actor appears three repeated times.

Answer 22

for movie in movies:

if movie.find("actor", 37, 42) == -1:
    print("Word not found")


elif movie.count("actor") == 2:  
    print(movie.replace("actor actor", "actor"))
else:


    print(movie.replace("actor actor actor", "actor"))

Question 23

Find the index where money occurs between characters with index 12 and 50. If not found, the method should return -1.

Answer 23

for movie in movies:
print(movie.find(“money”, 12, 51))

Question 24

Find the index where money occurs between characters with index 12 and 50. If not found, it should raise an error.

Answer 24

for movie in movies:
try:

print(movie.index(

“

money

”

, 12, 51))

except ValueError:
print(“substring not found”)

Question 25

my_string1 = “Awesome day”my_string2 = “for biking”

write concatenation to return:
Awesome day for biking

Answer 25

print(my_string1+” “+my_string2)

Question 26

my_string = “Awesome day”

return:
Awe

Answer 26

print(my_string[0:3])

Question 27

my_string = “Awesome day”

return: aweso
return:me day

Answer 27

print(my_string[:5])
print(my_string[5:])

Question 28

my_string = “Awesome day”

return: yad emosewA

Answer 28

print(my_string[::-1])

Question 29

Select the first 32 characters of movie1

Answer 29

first_part = movie1[:32]

Question 30

Select from 43rd character to the end of movie1

Answer 30

last_part = movie1[42:]

Question 31

Select from 33rd to the 42nd character of movie2

Answer 31

middle_part = movie2[32:42]

Question 32

Find out how many characters the variable movie has.

Answer 32

length_string = len(movie)

Question 33

Convert the numeric variable length_string to a string representation.
Then, Concatenate the predefined variable statement and the variable to_string adding a space between them. Print out the result.

Answer 33

to_string = str(length_string)

– Predefined variable

statement = “Number of characters in this review:”

– Concatenate strings and print result

print(statement+” “+ to_string)

Question 34

Select the first 32 characters of the variable movie1 and assign it to the variable first_part.

Answer 34

first_part = movie1[:32]

Question 35

Select the substring going from the 43rd character to the end of movie1. Assign it to the variable last_part.

Answer 35

last_part = movie1[42:]

Question 36

Select the substring going from the 33rd to the 42nd character of movie2. Assign it to the variable middle_part.

Answer 36

middle_part = movie2[32:42]

Question 37

Print the concatenation of the variables first_part, middle_part and last_part in that order.

Answer 37

print(first_part+middle_part+last_part)

Question 39

Convert the string in the variable movie to lowercase. Print the result.

Answer 39

movie_lower = movie.lower()
print(movie_lower)

Question 40

find all matches of a pattern

Answer 40

re.findall(r”regex”,string)

Question 41

Remove the $ that occur at the start and at the end of the string contained in movie_lower. Print the results.

Answer 41

movie_no_sign = movie_lower.strip(“$”)
print(movie_no_sign)

Question 42

Split the string contained in movie_no_sign into as many substrings as possible. Print the results.

Answer 42

movie_split = movie_no_sign.split()
print(movie_split)

Question 43

To get the root of the second word contained in movie_split, select all the characters except the last one.

Answer 43

word_root = movie_split[1][:-1]
print(word_root)

Question 44

Remove tag <\i> from the end of the string, movie. Print the results.

Answer 44

movie_tag = movie.rstrip(“<\i>”)

Question 45

what’s rstrip()?

Answer 45

remove trailing characters

Question 46

Join back together the list of substring contained in movie_no_comma using a space as a join element. Print the results.

Answer 46

movie_join = “ “.join(movie_no_comma)
print(movie_join)

Question 47

Find if the substring actor occurs between the characters with index 37 and 41 inclusive. If it is not detected, print the statement Word not found.

Answer 47

for movie in movies:

if movie.find("actor", 37, 42) == -1:
    print("Word not found")

Question 49

add elif to for statement to replace actor actor with the substring actor if actor occurs only two repeated times.

for movie in movies:
if movie.find(“actor”, 37, 42) == -1:
print(“Word not found”)

Answer 49

elif movie.count(“actor”) == 2:
print(movie.replace(“actor actor”, “actor”))

Question 50

Find the index where money occurs between characters with index 12 and 50. If not found, the method should return -1.

Answer 50

for movie in movies:
print(movie.find(“money”, 12, 51))

Question 51

Complete a for-loop to split the strings into many substrings using commas as a separator element.

Answer 51

for substring in file_split:
substring_split = substring.split(“,”)

Question 52

Split the string, file ,into many substrings at line boundaries.

Answer 52

file_split = file.splitlines()

Question 53

Import the re module.
Write a regex that matches the user mentions that starts with @ and follows the pattern, e.g. @robot3!.
Find all the matches of the pattern in the sentiment_analysis variable.

Answer 53

Import the re module
import re

Write the regex
regex = r”@robot\d\W”

Find all matches of regex
print(re.findall(regex, sentiment_analysis))

Question 54

Write a regex that matches the number of user mentions given as, for example, User_mentions:9 in sentiment_analysis.

Answer 54

print(re.findall(r”User_mentions:\d”, sentiment_analysis))

Question 55

Write a regex that matches the number of retweets given as, for example, number of retweets: 4 in sentiment_analysis.

Answer 55

print(re.findall(r”number\sof\sretweets:\s\d”, sentiment_analysis))