Strings

What are Strings

Strings are sequences of characters enclosed in quotes. They can be created using single quotes (‘), double quotes (“), or triple quotes (‘’’ or “””) for strings that span multiple lines.

# Examples of strings
single_quote_string = 'Hello, World!'
double_quote_string = "Hello, World!"
triple_quote_string = """This is a 
multi-line string."""

Basis String Operations

Indexing

Strings are indexed, starting at 0. A sequence of characters is stored in a string data type. So you can access each character of a string when using [].

my_string = "Hello"
print(my_string[0]) # Output: H
print(my_string[1]) # Output: e
print(my_string[4]) # Output: o

Concatenation (`+`)

Concatenation is the process of joining two or more strings together using the + operator.

greeting = "Hello"
name = "Alice"
full_greeting = greeting + ", " + name + "!"
print(full_greeting)
# Output: "Hello, Alice!"

Repetition (`*`)

Repetition is the process of repeating a string multiple times using the * operator.

repeat_greeting = "Hello! " * 3
print(repeat_greeting)
# Output: "Hello! Hello! Hello! "

Slicing (`:`)

Slicing allows you to extract a portion of a string using indices. The slice operator : is used to specify the start and end indices of the substring.

sample_string = "Hello, World!"
substring = sample_string[0:5]
print(substring)
# Output: "Hello"

Built-in String Functions

Python provides several built-in methods for string manipulation.

The print() function outputs strings (or other data types) to the console. We have used that function before.

# Print a string
print("Hello, World!")
# Output: Hello, World!

# Print a string variable
message = "Hello, Python!"
print(message)
# Output: Hello, Python!

The len() function returns the length of a string.

length = len("Hello, World!")
print(length)
# Output: 13

The str() function converts other data types to strings.

number = 42
number_string = str(number)
print(number_string)
# Output: '42'

Built-in String Methods

The replace() method replaces occurrences of a substring with another substring.

original_string = "Hello, World!"
new_string = original_string.replace("World", "Python")
print(new_string)
# Output: "Hello, Python!"

The find() method returns the lowest index of the first occurrence of a substring, while rfind() returns the highest index of the last occurrence.

# Find first occurrence
text = "Hello, World! Hello, Python!"
index_hello = text.find("Hello")
# Output: 0

# Find last occurrence
index_hello_last = text.rfind("Hello")
# Output: 13

The count() method returns the number of occurrences of a substring in a string.

text = "Hello, World! Hello, Python!"
count_hello = text.count("Hello")
# Output: 2

The split() method splits a string into a list of substrings based on a delimiter.

# Splits string at all spaces
sentence = "Hello, World! How are you?"
words = sentence.split(" ")
# Output: ['Hello,', 'World!', 'How', 'are', 'you?']

The splitlines() method splits a string at line breaks and returns a list of lines.

# Split string into lines
multiline_string = """This is line one.
This is line two.
This is line three."""
lines = multiline_string.splitlines()
# Output: ['This is line one.', 'This is line two.', 'This is line three.']

String Methods in Python

Method/Function	Description
`str.lower()`	Converts all characters in the string to lowercase.
`str.upper()`	Converts all characters in the string to uppercase.
`str.title()`	Converts the first character of each word to uppercase and the rest to lowercase.
`str.capitalize()`	Capitalizes the first character of the string and lowers all other characters.
`str.strip()`	Removes any leading and trailing whitespace from the string.
`str.split(separator)`	Splits the string into a list of substrings based on the specified separator.
`str.join(iterable)`	Concatenates a list or tuple of strings into a single string, separated by the string used to call the method.
`str.replace(old, new)`	Replaces all occurrences of a substring with another substring.
`str.find(substring)`	Returns the lowest index of the substring if found in the string; otherwise, it returns -1.
`str.rfind(substring)`	Returns the highest index of the substring if found in the string; otherwise, it returns -1.
`str.count(substring)`	Returns the number of occurrences of a substring in the string.
`str.startswith(prefix)`	Returns `True` if the string starts with the specified prefix; otherwise, it returns `False`.
`str.endswith(suffix)`	Returns `True` if the string ends with the specified suffix; otherwise, it returns `False`.
`str.isdigit()`	Returns `True` if all characters in the string are digits; otherwise, it returns `False`.
`str.isalpha()`	Returns `True` if all characters in the string are alphabetic; otherwise, it returns `False`.
`str.isalnum()`	Returns `True` if all characters in the string are alphanumeric; otherwise, it returns `False`.
`str.format(args, *kwargs)`	Formats the string using the specified arguments or keyword arguments.