Strings

In Python, strings are a sequence of characters, and Python provides a wide range of methods and functions to manipulate them. 
Here's a comprehensive guide to string operations, methods, and functions:

String Creation and Basics

# Strings can be created using single, double, or triple quotes

single_quoted = 'Hello'

double_quoted = "Hello"

triple_quoted = '''Hello'''

triple_quoted_multiline = '''This is a 
multiline string'''

String Operators

Concatenation (+): Combines two strings.
result = 'Hello' + ' ' + 'World'

Repetition (*): Repeats a string multiple times.
result = 'Hi!' * 3  # Output: 'Hi!Hi!Hi!'

Membership (in / not in): Checks if a substring is in a string.
'H' in 'Hello'  # True
'z' not in 'Hello'  # True


String Methods

1. Basic Methods

len(string): Returns the length of the string.
len('Hello')  # Output: 5


str(): Converts any data type to a string.
str(123)  # Output: '123'


2. Case Manipulation

lower(): Converts all characters to lowercase.
'Hello'.lower()  # Output: 'hello'


upper(): Converts all characters to uppercase.
'Hello'.upper()  # Output: 'HELLO'


capitalize(): Converts the first character to uppercase.
'hello'.capitalize()  # Output: 'Hello'


title(): Converts the first character of each word to uppercase.
'hello world'.title()  # Output: 'Hello World'


swapcase(): Swaps the case of all characters.
'Hello World'.swapcase()  # Output: 'hELLO wORLD'


3. Whitespace Removal

strip(): Removes leading and trailing whitespace.

'  Hello  '.strip()  # Output: 'Hello'

lstrip(): Removes leading whitespace.

'  Hello'.lstrip()  # Output: 'Hello'

rstrip(): Removes trailing whitespace.

'Hello  '.rstrip()  # Output: 'Hello'


4. Searching and Replacing

find(substring): Returns the index of the first occurrence of substring, or -1 if not found.
'Hello'.find('e')  # Output: 1


rfind(substring): Returns the index of the last occurrence of substring.
'Hello'.rfind('l')  # Output: 3


index(substring): Like find(), but raises a ValueError if not found.
'Hello'.index('e')  # Output: 1


replace(old, new): Replaces all occurrences of old with new.
'Hello World'.replace('World', 'Python')  # Output: 'Hello Python'


5. String Splitting and Joining

split(separator): Splits the string into a list of substrings.
'Hello World'.split()  # Output: ['Hello', 'World']

rsplit(separator): Splits from the right.
'a,b,c'.rsplit(',', 1)  # Output: ['a,b', 'c']


splitlines(): Splits the string at line breaks (\n).
'Line1\nLine2\nLine3'.splitlines()  # Output: ['Line1', 'Line2', 'Line3']


join(iterable): Joins the elements of an iterable (e.g., list) into a single string, using the string as a separator.
','.join(['a', 'b', 'c'])  # Output: 'a,b,c'


6. Character Checks


These methods return True or False based on the string's content:
isalpha(): Checks if all characters are alphabetic.
'Hello'.isalpha()  # Output: True


isdigit(): Checks if all characters are digits.
'12345'.isdigit()  # Output: True


isalnum(): Checks if all characters are alphanumeric (letters and numbers).
'Hello123'.isalnum()  # Output: True


isspace(): Checks if all characters are whitespace.
'   '.isspace()  # Output: True


istitle(): Checks if the string is title-cased (first letter of each word is uppercase).
'Hello World'.istitle()  # Output: True


7. String Alignment

center(width, fillchar=' '): Centers the string, padding with fillchar.
'Hello'.center(10, '-')  # Output: '--Hello---'


ljust(width, fillchar=' '): Left-justifies the string.
'Hello'.ljust(10, '-')  # Output: 'Hello-----'


rjust(width, fillchar=' '): Right-justifies the string.
'Hello'.rjust(10, '-')  # Output: '-----Hello'


String Formatting


1. format() Method

You can insert values into a string using placeholders {}:
'My name is {}'.format('John')  # Output: 'My name is John'


Positional and keyword arguments:
'Coordinates: {}, {}'.format(10, 20)  # Output: 'Coordinates: 10, 20'
'Name: {first} {last}'.format(first='John', last='Doe')  # Output: 'Name: John Doe'


2. Formatted String Literals (f-strings)

Introduced in Python 3.6, f-strings allow embedding expressions inside string literals using {}.
name = 'John'
age = 30
f'My name is {name} and I am {age} years old'  # Output: 'My name is John and I am 30 years old'


3. % Operator (Old-style)
The % operator allows formatting similar to C's printf.
'Hello, %s' % 'World'  # Output: 'Hello, World'
'Age: %d' % 30  # Output: 'Age: 30'


String Encoding and Decoding

encode(encoding='utf-8'): Encodes the string to bytes using the specified encoding.
'Hello'.encode('utf-8')  # Output: b'Hello'


decode(encoding='utf-8'): Decodes bytes to a string.
b'Hello'.decode('utf-8')  # Output: 'Hello'

String Slicing

Strings in Python can be sliced to extract substrings.

list[start:end]  -->  from index start to (end-1)

list[start:]  ---> from index start to end of the list

list[:end] -->  from index 0 to end-1

list[:]  --> copy of whole array

Examples:
s = 'Hello World'
s[0:5]  # Output: 'Hello' (characters from index 0 to 4)
s[:5]   # Output: 'Hello' (same as above)
s[6:]   # Output: 'World' (characters from index 6 to end)
s[-5:]  # Output: 'World' (last 5 characters)


Common String Functions
max(): Returns the character with the maximum ASCII value.
max('Hello')  # Output: 'o'

min(): Returns the character with the minimum ASCII value.
min('Hello')  # Output: 'H'


ord(): Returns the ASCII value of a character.
ord('A')  # Output: 65


chr(): Returns the character for an ASCII value.
chr(65)  # Output: 'A'

This guide covers the majority of string methods and functions available in Python.