Strings

adapted from Medium.com

Let us see the different operations that can be performed on the below string.

word = 'Sample'
len(word)
# 6

 +---+---+---+---+---+---+
 | S | a | m | p | l | e |
 +---+---+---+---+---+---+
 0   1   2   3   4   5   6
-6  -5  -4  -3  -2  -1

1 Concatenation

Join a string with another string

word = 'Sample'
word + ' ' + 'trick'
# 'Sample trick'

2 Indexed Access of Strings

A string in a python can be indexed to perform operations on the string.

Positive single character

word = 'Sample'
word[3]
# 'p'

Negative single character

word = 'Sample'
word[-2]
# 'l'

String Reverse

word = 'Sample'
word[::-1]
# 'elpmaS'

Reverse string by iterating through string contents.

word = 'Sample'
for char in reversed(word):    
    print(char)

### Output ###
e
l
p
m
a
S

3 Slicing of Strings

Slicing allows us to access a substring of characters from a word.

Example 1
word = 'Sample'
word[0:3]
# 'Sam'

Example 2
word = 'Sample'
word[4:5]
# 'le'

Example 3
word = 'Sample'
word[:5]
# 'Sampl'

4 Remove leading and trailing characters

To remove space before and after a string the strip() method can be used has shown below

'   Sample   '.strip()
# 'Sample'
'sample'.strip('ple')
# 'sam'

5 Left fill with ASCII ‘0’

To left fill with ASCII ‘0’’, we can use zfill() method to make a length of required string width.

"10".zfill(6)
# '000010'
"-10".zfill(6)
# '-00010'

6 Find Substring

The find() method can be used to extract a substring from a string

'sample'.find('am',0,5)
# '1'
'sam' in 'sample'
# True

7 Find if the string contains Numbers

The isalpha() method can be used to find if a string contains number

'123'.isalpha()
# False
'abc'.isalpha()
# True
'1abc'.isalpha()
# False

8 Find if the string is alphanumeric

The isalnum() method can be used to find if the string contains alphanumeric and at least one character

' '.isalnum()
# False
'abc'.isalnum()
# True

9 Find if the string is having only whitespace

The isspace() method can be used to determine if the string is only whitespace character

' '.isspace()
# True
'Sample  '.isspace()
# False

10 Remove Spaces on the left side of the string

The lstrip() Strings can be used to remove whitespace characters on the left.

'   sample   '.lstrip()
# 'spacious   '
'www.example.com'.lstrip('cmowz.')
# 'example.com'

11 Remove Spaces on the right side of the string

The rstrip() can be used to remove whitespace characters on the left.

'   sample   '.rstrip()
# 'spacious   '
'mississippi'.rstrip('ipz')
# 'mississ'

12 Formatted String Literals

The string literals which are prefixed with ‘f’ or ’F’ are called f-string.

word = "Sample"
f"THis is a {word!r} string."
# "THis is a 'Sample' string."

13 Joining multiple strings from a list

The join() method can be used to join the strings in a list

Test = ["This","is","Sample"]
print(" ".join(Test))
# This is Sample

14 Repeat string multiple times

Same like nos the strings can be multiplied to generate multiple string

word = "Sample"
print(word*3)
# SampleSampleSample

15 Search for multiple prefixes in a string

The startswith() and endswith() method can be passed with multiple patterns of substrings to check if it is present.

"sample".startswith(("sam","Sam"))
# True
"sample".endswith(("ple","ple."))
# True

16 Splitting a sentence to word

The split() method can be used to split a sentence to multiple words to form a list

"This is a Sample".split()
# ['This', 'is', 'a', 'Sample']

17 Find the frequent word in a sentence

The word which occurs most times in a sentence can be found using the below trick

sentence = "She was young the way an actual young person is young"
split_sentence = sentence.split()
most_frequent_word = max(set(split_sentence),key=split_sentence.count)
# 'young'

18 Find how many occurences of words in a sentence

The below trick helps in finding, how many times the word is present in the sentence sorted by the increasing rate of word occurence.

from collections import Counter
sentence = "She was young the way an actual young person is young"
split_sentence = sentence.split()
Counter(split_sentence)
# Counter({'young': 3, 'She': 1, 'was': 1, 'the': 1, 'way': 1, 'an': 1, 'actual': 1, 'person': 1, 'is': 1})

19 Convert all the words to capital in a sentence

The map() method can be used to make all words to capital letters.

sentence = "Quick brown fox".split()
list(map(str.capitalize,sentence))
# ['Quick', 'Brown', 'Fox']

20 Remove duplicate words in a sentence

Duplicate words in a sentence can be removed has shown below

sentence = "The sound sounds sound".split()
list(set(sentence))
# ['sound', 'The', 'sounds']

21 Remove duplicate words retain the sentence order

The below trick removes the duplicate word keeping the order of words in the sentence.

from collections import OrderedDict
sentence = "The sound sounds sound".split()
list(OrderedDict.fromkeys(sentence).keys())
# ['The', 'sound', 'sounds']

22 Reversing a sentence

The reverse() method can be used to reverse a sentence

sentence = "This is Sample".split()
sentence.reverse()
print(sentence)
# ['Sample', 'is', 'This']

23 Splitting words to multiple string

The below trick can be used to split a sentence into multiple words and storing in a string variable.

sentence = "This is Sample".split()
first_word, second_word, third_word = sentence
print(first_word)
print(second_word)
print(third_word)

24 Combine list using zip() method

The zip() method can be used to combine two seperate list of strings.

Name = ['Tom', 'Marry', 'Jon']
Age = ['35', '30', '40']
for Name, Age in zip(Name,Age):
    print(Name,Age)
###  Output ###
Tom 35
Marry 30
Jon 40

25 Sort words in a list using sorted() method

The sorted() method can be used to sort the list of strings.

sorted(['string1','string2','string3'],reverse=True)
# ['string3', 'string2', 'string1']