Strings in Python - Interview Questions and Answers

A string is a sequence of characters enclosed in single, double, or triple quotes (', ", ''')

string1 = 'Hello'
string2 = "World"
string3 = '''Multiline
String'''

By indexing:

string = "Python"
print(string[0])  # P
print(string[-1])  # n

Using the len() function

string = "Hello"
print(len(string))  # 5

Extracting a substring using start:end:step

string = "Python"
print(string[1:4])  # yth
print(string[:3])  # Pyt
print(string[::2])  # Pto

No, strings are immutable in Python, meaning their content cannot be changed after creation.

Functionally, there?s no difference. Double quotes are often used when the string contains a single quote:

string = "It's a string"

Using +:

print("Hello" + " " + "World")  # Hello World

Using *

print("Python " * 3)  # Python Python Python

Using str()

num = 123
print(str(num))  # '123'

Using the in keyword:

print("Py" in "Python")  # True

Use lower() and upper()

string = "Python"
print(string.lower())  # python
print(string.upper())  # PYTHON

Use strip()

string = "  Hello  "
print(string.strip())  # 'Hello'

find() returns -1 if the substring is not found, while index() raises a ValueError.

Using replace():

string = "Hello World"
print(string.replace("World", "Python"))  # Hello Python

Using split()

string = "a,b,c"
print(string.split(","))  # ['a', 'b', 'c']

Using join():

list_strings = ["a", "b", "c"]
print(",".join(list_strings))  # a,b,c

Inserting variables into strings using f-strings or .format()

name = "Alice"
print(f"Hello, {name}!")  # Hello, Alice!

Checks if a string is alphanumeric (contains only letters and numbers).

isalpha(): Checks if all characters are alphabetic.
isdigit(): Checks if all characters are digits.

Using slicing:

string = "Python"
print(string[::-1])  # nohtyP

Strings prefixed with r to prevent escape sequences:

raw_string = r"C:\new_folder"
print(raw_string)  # C:\new_folder

Pads a string with zeros to the left:

print("42".zfill(5))  # 00042

Using startswith() and endswith()

print("Python".startswith("Py"))  # True
print("Python".endswith("on"))  # True

Using count():

print("banana".count("a"))  # 3

Using format() or f-strings

print(f"{1000000:,}")  # 1,000,000

capitalize(): Capitalizes the first character of the string.
title(): Capitalizes the first character of each word.

Unicode is a standard for encoding text in multiple languages. Python strings support Unicode by default.

Using encode() and decode()

encoded = "Hello".encode("utf-8")
decoded = encoded.decode("utf-8")

By reversing and comparing

string = "madam"
print(string == string[::-1])  # True

Formats a string using a dictionary:

data = {"name": "Alice", "age": 30}
print("{name} is {age}".format_map(data))  # Alice is 30

split() splits from the left, rsplit() splits from the right.

Using ord()

print(ord("A"))  # 65

Using chr()

print(chr(65))  # A

Replaces characters based on a translation table:

table = str.maketrans("aeiou", "12345")
print("apple".translate(table))  # 1ppl2

Using replace() or translate():

print("hello!".replace("!", ""))  # hello

Splits a string into three parts: before, separator, and after

print("Hello,World".partition(","))  # ('Hello', ',', 'World')

Using sorted()

print("dcba".join(sorted("dcba")))  # abcd

Using isspace()

Expands tab characters to spaces:

print("Hello\tWorld".expandtabs(4))

join() is faster and more efficient for combining multiple strings, especially when dealing with lists. Concatenation (+) is simpler for combining two or three strings.

# Using join
words = ["Python", "is", "fun"]
print(" ".join(words))  # Python is fun

# Using concatenation
print("Python" + " is " + "fun")  # Python is fun

Use a set() to extract unique characters:

string = "programming"
unique_chars = set(string)
print(unique_chars)  # {'g', 'r', 'a', 'o', 'n', 'm', 'i', 'p'}

Strings in Python are immutable, meaning their content cannot be changed after creation. Any modification creates a new string.

string = "Python"
string[0] = "J"  # This raises a TypeError
string = "Java"  # Creates a new string

Escape sequences allow special characters (like newline \n, tab \t) to be included in strings.

print("Hello\nWorld")  # Outputs:
# Hello
# World

Using set() and join()

string = "programming"
result = "".join(set(string))
print(result)  # The order may vary

Python does not copy the sliced string into a new memory location. It uses the original string, which improves performance.

Use the split() method or nltk library for advanced tokenization

string = "Python is fun"
tokens = string.split()  # ['Python', 'is', 'fun']

String literals are strings explicitly defined in code, enclosed in quotes

string = "Hello"  # This is a string literal

Using isupper():

print("PYTHON".isupper())  # True
print("Python".isupper())  # False

casefold() is used for case-insensitive comparisons. It converts strings to lowercase, considering language-specific cases.

print("?".casefold())  # 'ss'

Use f-strings, format(), or % formatting

name = "Alice"
print(f"Hello, {name}")  # Hello, Alice

strip(): Removes leading and trailing spaces.
lstrip(): Removes leading spaces.
rstrip(): Removes trailing spaces.

string = "  Hello  "
print(string.strip())  # 'Hello'
print(string.lstrip())  # 'Hello  '
print(string.rstrip())  # '  Hello'

Using isnumeric():

print("123".isnumeric())  # True
print("123a".isnumeric())  # False

isdecimal() checks for decimal characters (0-9).
isdigit() includes decimal characters, superscripts, etc.

print("123".isdecimal())  # True
print("?".isdigit())  # True

Strings enclosed in triple quotes (''' or """) can span multiple lines

string = '''This is
a multiline
string.'''

Use a combination of split(), find(), or regular expressions:

import re
email = "test@example.com"
print(bool(re.match(r"[^@]+@[^@]+\.[^@]+", email)))  # True

Use if not string

string = ""
print(not string)  # True

These methods align strings to the left, right, or center

string = "Python"
print(string.ljust(10, "-"))  # Python----
print(string.rjust(10, "-"))  # ----Python
print(string.center(10, "-"))  # --Python--

Strings in Python support Unicode by default. Use encode() to convert to bytes and decode() to convert back.

string = "caf?"
encoded = string.encode("utf-8")
print(encoded)  # b'caf\xc3\xa9'
print(encoded.decode("utf-8"))  # caf?

Using a loop or comprehension:

string = "Hello World"
vowels = "aeiouAEIOU"
count = sum(1 for char in string if char in vowels)
print(count)  # 3