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Strings

Definition of a String​

  • A string is a sequence of characters, essentially text data. In Python, a string is represented by enclosing characters within either single (') or double quotes (").
  • Example:
    strings.py
    name = "John"
    greeting = 'Hello, world!'

Creating Strings​

  • Strings can be assigned to variables:
    strings.py
    city = "San Francisco"
  • Double vs. Single Quotes:
    • You can use both single or double quotes to create strings.
    • The opening and closing quotes must match.
    • Example:
      strings.py
      sentence = 'It\'s a sunny day'
      # Alternatively, using double quotes avoids the need to escape the single quote:
      sentence = "It's a sunny day"

Multi-line Strings​

  • For multi-line strings, use triple quotes (''' or """).
  • Example:
    strings.py
    address = """123 Elm Street
    Springfield
    USA"""
  • This allows the string to span multiple lines.

String Concatenation​

  • You can concatenate (join) strings using the + operator:
    strings.py
    full_name = "John" + " " + "Doe"
    # Output: "John Doe"
  • Note that spaces between words must be explicitly added, as shown.

String Length​

  • Use the len() function to get the length of a string:
    strings.py
    length = len(full_name)
    print("Length of the full name:", length)
    # Output: 8

String Repetition​

  • You can repeat a string using the * operator:
    strings.py
    dash_line = "-" * 5
    # Output: "-----"

String Methods​

  • upper(): Converts all characters to uppercase.
    strings.py
    greeting = "hello"
    print(greeting.upper())  # Output: "HELLO"
  • lower(): Converts all characters to lowercase.
    strings.py
    print(greeting.lower())  # Output: "hello"
  • title(): Converts the first character of each word to uppercase.
    strings.py
    title_greeting = "welcome to python"
    print(title_greeting.title())  # Output: "Welcome To Python"

Whitespace Removal​

  • strip(): Removes leading and trailing whitespace.
    strings.py
    spaced_string = "  Hello  "
    print(spaced_string.strip())  # Output: "Hello"
  • lstrip(): Removes leading whitespace only.
  • rstrip(): Removes trailing whitespace only.

Replacing Substrings​

  • replace(old, new): Replaces all occurrences of old with new in the string.
    strings.py
    text = "I like apples"
    new_text = text.replace("apples", "bananas")
    print(new_text)  # Output: "I like bananas"

Finding Substrings​

  • count(sub): Counts how many times a substring appears in the string.
    strings.py
    phrase = "banana"
    print(phrase.count("a"))  # Output: 3
  • find(sub): Returns the index of the first occurrence of the substring. If not found, returns -1.
    strings.py
    print(phrase.find("na"))  # Output: 2

Accessing Characters in a String​

  • You can access individual characters in a string using indexing with square brackets.
  • Index starts at 0 (first character):
    strings.py
    first_char = phrase[0]  # Output: 'b'
  • Negative indexing starts from the end:
    strings.py
    last_char = phrase[-1]  # Output: 'a'

Comments and Disabling Code​

  • Use the # symbol to add comments to your code.
  • Example:
    strings.py
    # This is a comment
    print("Hello, World!")  # This line prints a greeting
  • You can comment out lines of code to prevent them from executing, especially useful during debugging:
    strings.py
    # print("This line won't run")
    print("This line will run")

String Slicing​

  • You can extract substrings using slicing syntax [start:end]:
    strings.py
    text = "Python programming"
    sub_text = text[0:6]  # Output: "Python"
  • start is inclusive, end is exclusive.

This overview gives a foundational understanding of working with strings in Python, covering creating, manipulating, and accessing string data effectively.