String Data Type in python Class 11 Notes

String Data Type in python

WHAT ARE STRINGS?

In Python, a string is a sequence of characters, enclosed in either single quotes (”) or double quotes (“”). Strings are immutable, which means once a string is created, its contents cannot be changed.

Here is an example of a string:

my_string = "Hello, World!"

You can access individual characters within a string using indexing. The index of the first character in a string is 0, and you can count backwards from the end of the string using negative indices. Here are some examples:

first_char = my_string[0]      # returns 'H'
last_char = my_string[-1]      # returns '!'

You can also slice a string to extract a substring. Slicing is done using the colon (:) operator. The syntax for slicing is [start_index:end_index], where start_index is the index of the first character you want to include in the substring, and end_index is the index of the first character you want to exclude from the substring. If you omit start_index, Python assumes you want to start at the beginning of the string, and if you omit end_index, Python assumes you want to go to the end of the string. Here are some examples:

substring = my_string[0:5]    # returns 'Hello'
substring2 = my_string[7:]    # returns 'World!'

You can also concatenate two or more strings using the + operator. Here is an example:

greeting = "Hello"
name = "Alice"
full_greeting = greeting + ", " + name + "!"

This would set full_greeting to "Hello, Alice!".

here are some more operations and methods you can perform on strings in Python:

• len(string): returns the length of the string

my_string = "Hello, World!"
length = len(my_string)   # returns 13

string.upper(): returns a new string with all characters in uppercase

my_string = "Hello, World!"
uppercase_string = my_string.upper()   # returns "HELLO, WORLD!"

string.lower(): returns a new string with all characters in lowercase

my_string = "Hello, World!"
lowercase_string = my_string.lower()   # returns "hello, world!"

string.strip(): returns a new string with leading and trailing whitespace removed

my_string = "  Hello, World!  "
stripped_string = my_string.strip()   # returns "Hello, World!"

string.replace(old, new): returns a new string with all occurrences of old replaced by new

my_string = "Hello, World!"
new_string = my_string.replace("World", "Python")   # returns "Hello, Python!"

string.split(separator): returns a list of substrings, split by the specified separator (default is whitespace)

my_string = "Hello, World!"
words = my_string.split(",")   # returns ["Hello", " World!"]

string.join(iterable): returns a new string by concatenating the elements of an iterable, separated by the string

words = ["Hello", "World", "!"]
my_string = ", ".join(words)   # returns "Hello, World, !"

string.format(): allows you to insert values into a string using placeholders

name = "Alice"
age = 30
greeting = "Hello, my name is {} and I am {} years old.".format(name, age)

my_string = "Hello, World!"
starts_with_hello = my_string.startswith("Hello")   # returns True

my_string = "Hello, World!"
ends_with_exclamation = my_string.endswith("!")   # returns True

my_string = "Hello, World!"
index_of_world = my_string.find("World")   # returns 7

string.count(substring): returns the number of times the specified substring appears in the string.

my_string = "Hello, World!"
number_of_l = my_string.count("l")   # returns 3

string.isalpha(): returns True if all characters in the string are alphabetic, False otherwise.

my_string = "Hello, World!"
is_alpha = my_string.isalpha()   # returns False (because of the comma and the space)

string.isdigit(): returns True if all characters in the string are digits, False otherwise.

my_string = "12345"
is_digit = my_string.isdigit()   # returns True

string.islower(): returns True if all alphabetic characters in the string are lowercase, False otherwise.

my_string = "hello, world!"
is_lower = my_string.islower()   # returns True

string.isupper(): returns True if all alphabetic characters in the string are uppercase, False otherwise.

my_string = "HELLO, WORLD!"
is_upper = my_string.isupper()   # returns True

string.encode(): returns a bytes object encoding the string using the specified encoding (default is UTF-8)

my_string = "Hello, World!"
encoded_bytes = my_string.encode()   # returns b'Hello, World!'

string.center(width): returns a new string centered within a string of a specified width, with any extra space filled by a specified character (default is whitespace).

my_string = "Hello, World!"
centered_string = my_string.center(20, "*")   # returns "***Hello, World!***"

string.ljust(width): returns a new string left-justified within a string of a specified width, with any extra space filled by a specified character (default is whitespace).

my_string = "Hello, World!"
left_justified_string = my_string.ljust(20, "*")   # returns "Hello, World!*******"

string.rjust(width): returns a new string right-justified within a string of a specified width, with any extra space filled by a specified character (default is whitespace).

my_string = "Hello, World!"
right_justified_string = my_string.rjust(20, "*")   # returns "*******Hello, World!"

string.swapcase(): returns a new string with uppercase characters converted to lowercase and vice versa.

my_string = "Hello, World!"
swapped_case_string = my_string.swapcase()   # returns "hELLO, wORLD!"

string.title(): returns a new string with the first letter of each word capitalized.

my_string = "hello, world!"
title_string = my_string.title()   # returns "Hello, World!"

string.capitalize(): returns a new string with the first character capitalized and the rest in lowercase.

my_string = "hello, world!"
capitalized_string = my_string.capitalize()   # returns "Hello, world!"