• Python Features
• Python Installation
• PyCharm Configuration
• Python Variables
• Python Data Types
• Python If Else
• Python Loops
• Python Strings
  • String Methods
  • String Programs
  • String MCQs
• Python Lists
• Python Tuples
• Python List Vs Tuple
• Python Sets
• Python Dictionary
• Python Functions
• Python Files I/O
• Read Write Excel
• Read Write JSON
• Read Write CSV
• Python OS Module
• Python Exceptions
• Python Datetime
• Python Collection Module
• Python Sys Module
• Python Decorator
• Python Generators
• Python OOPS
• Python Numpy Module
• Python Pandas Module
• Python Sqlite Module

String Introduction:

A string is a sequence of characters. In Python, you can define a string using either single quotes (‘) or double quotes (“), or triple quotes (”’ or “””) for multiline strings. Here are some examples:

# Defining strings in Python

# Single-quoted string
single_quote_str = 'Hello, World!'
print("Single-quoted string:", single_quote_str)

# Double-quoted string
double_quote_str = "Hello, Python!"
print("Double-quoted string:", double_quote_str)

# Triple-quoted string (for multiline text)
triple_quote_str = '''This is a
multiline string.
It spans multiple lines.'''
print("Triple-quoted string:")
print(triple_quote_str)

Re-assign Strings:

In Python, you can reassign a string to a new value by simply assigning the new value to the variable that holds the string.  Here’s an example:

# Initial string assignment
my_string = "Hello, World!"
print("Original string:", my_string)

# Reassigning the string to a new value
my_string = "Welcome to Python!"
print("Reassigned string:", my_string)

In the example above, the first print statement outputs “Hello, World!” because my_string is initially assigned that value. Then, my_string is reassigned to “Sqatools” and the second print statement outputs the new value.

# Example to demonstrate string immutability in Python

# 1). String Concatenation
greeting = "Hello"
new_greeting = greeting + ", World!"
print("Original string (after concatenation):", greeting)  # Output: Hello
print("New string (concatenation result):", new_greeting)  # Output: Hello, World!

# 2). String Replacement
my_string = "Hello, Python!"
new_string = my_string.replace("Python", "World")
print("\nOriginal string (after replacement):", my_string)  # Output: Hello, Python!
print("New string (replacement result):", new_string)       # Output: Hello, World!

# 3). String Slicing
text = "Immutable"
sliced_text = text[:3]  # Taking the first three characters
print("\nOriginal string (after slicing):", text)           # Output: Immutable
print("Sliced string (slicing result):", sliced_text)       # Output: Imm

Deleting string:

In Python, you cannot delete individual characters in a string because strings are immutable. However, you can delete the entire string object from memory using the del statement.  Here’s an example:

# Define a string
my_string = "Hello, World!"
print(my_string)  # Outputs: Hello, World!

# Delete the string object
del my_string

# Try to access the deleted string
try:
    print(my_string)
except NameError as e:
    print(e)  # Outputs: name 'my_string' is not defined

In the example above, the first print statement outputs the value of my_string, which is “Hello, World!”. Then, the del statement deletes the my_string object from memory. When we try to print my_string again, we get a NameError because the variable no longer exists.

String formatting methods:

Python provides several methods for formatting strings. Here are the most commonly used methods:

1. The % operator: This operator allows you to format strings using placeholders, which are replaced with values at runtime. Here’s an example:

# Using the % operator for string formatting
name = "Alice"
age = 25

formatted_string = "My name is %s and I am %d years old." % (name, age)
print(formatted_string)
# Output: My name is Alice and I am 25 years old.

In the example above, %s and %d are placeholders for the name and age variables, respectively. The values of these variables are provided in a tuple that follows the % operator.

2. The str.format() method: This method allows you to format strings using placeholders that are enclosed in curly braces. Here’s an example:

# Using the str.format() method for string formatting
name = "Alice"
age = 25

formatted_string = "My name is {} and I am {} years old.".format(name, age)
print(formatted_string)
# Output: My name is Alice and I am 25 years old.

In the example above, {} is a placeholder for the name and age variables. The values of these variables are provided as arguments to the str.format() method.

3. F-strings: It allows you to embed expressions inside placeholders that are enclosed in curly braces preceded by the f character. Here’s an example:

# Using f-strings for string formatting
name = "Alice"
age = 25

# Embedding variables directly into the string
formatted_string = f"My name is {name} and I am {age} years old."
print(formatted_string)
# Output: My name is Alice and I am 25 years old.

In the example above, the f character before the string indicates that it is an f-string. The expressions inside the curly braces are evaluated at runtime and the resulting values are inserted into the string.

String operators:

In Python, strings support several operators that can be used to perform various operations on strings. Here are some of the most commonly used string operators:

1. Concatenation (+): The + operator can be used to concatenate two or more strings. Here’s an example:

# Using the + operator to concatenate strings
str1 = "Hello"
str2 = "World"
combined_str = str1 + " " + str2  # Adding a space between the words

print(combined_str)
# Output: Hello World

2. Repetition (*): The * operator can be used to repeat a string a certain number of times. Here’s an example:

# Using the * operator to repeat a string
str1 = "Hello "
repeated_str = str1 * 3  # Repeating the string 3 times

print(repeated_str)
# Output: Hello Hello Hello 

3. Membership (in): The in operator can be used to check if a substring exists within a string. It returns True if the substring is found, and False otherwise. Here’s an example:

# Using the 'in' operator to check membership
sentence = "Python is awesome!"

# Checking if a substring exists within the string
substring = "Python"
result = substring in sentence

print(result)
# Output: True

4. Indexing ([]): The [] operator can be used to access individual characters within a string. You can use a positive index to access characters from the beginning of the string, and a negative index to access characters from the end of the string. Here’s an example:

# Using the [] operator for indexing a string
my_string = "Python"

# Accessing characters using positive indices
first_char = my_string[0]  # First character
last_char = my_string[5]   # Last character (index 5 for "n")

print("First character:", first_char)  # Output: P
print("Last character:", last_char)    # Output: n

# Accessing characters using negative indices
second_last_char = my_string[-2]  # Second last character (index -2 for "o")
print("Second last character:", second_last_char)  # Output: o

5. Slicing ([start:end]): The [] operator can also be used to extract a substring (or slice) from a string. The start argument specifies the starting index of the slice (inclusive), and the end argument specifies the ending index of the slice (exclusive). Here’s an example:

# Using the [] operator for string slicing
my_string = "Python Programming"

# Extracting a substring using slicing
substring = my_string[0:6]  # From index 0 to 5 (6 is exclusive)
print(substring)  # Output: Python

6. Comparison (==, !=, <, <=, >, >=): The comparison operators can be used to compare two strings alphabetically.

# Comparison of strings using various operators
string1 = "Apple"
string2 = "Banana"

# Checking if the strings are equal
print(string1 == string2)  # Output: False

# Checking if the strings are not equal
print(string1 != string2)  # Output: True

# Checking if string1 is alphabetically less than string2
print(string1 < string2)   # Output: True

# Checking if string1 is alphabetically greater than string2
print(string1 > string2)   # Output: False

# Checking if string1 is alphabetically less than or equal to string2
print(string1 <= string2)  # Output: True

# Checking if string1 is alphabetically greater than or equal to string2
print(string1 >= string2)  # Output: False

String indexing and slicing:

Indexing:

Indexing: Each character in a string is assigned an index starting from 0. You can access a particular character in a string using its index. Here’s an example:

# Using indexing to access characters in a string
my_string = "Python"

# Accessing individual characters using their indices
first_char = my_string[0]  # First character
second_char = my_string[1]  # Second character
last_char = my_string[5]  # Last character

print("First character:", first_char)  # Output: P
print("Second character:", second_char)  # Output: y
print("Last character:", last_char)  # Output: n

Slicing:

You can extract a portion of a string using slicing. Slicing is done using the [] operator, with two indices separated by a colon (:) inside the brackets. Here’s an example:

# Using slicing to extract a portion of a string
my_string = "Python Programming"

# Slicing from index 0 to 6 (exclusive of index 6)
substring = my_string[0:6]  # This gives 'Python'

print(substring)  # Output: Python

In the example above, my_string[0:5] returns the first five characters of the string, my_string[:5] returns all the characters up to the fifth character, and my_string[-5:] returns the characters from the fifth-last to the last character.

Note that the first index in a slice is inclusive and the second index is exclusive. So, my_string[0:5] returns characters from index 0 to index 4, but not the character at index 5.

In addition to the two indices separated by a colon, you can also add a third index to specify the step value. Here’s an example:

# Using slicing with a step
my_string = "Python Programming"

# Extracting every second character from index 0 to index 12
substring = my_string[0:13:2]  # From index 0 to 12, taking every second character

print(substring)  # Output: Pto rg