1.2 Input/output

Input and output functions are essential for interacting with users and managing data flow in Python programs. These functions allow you to display information, collect user input, and convert data types for calculations.

Understanding how to use print() and input() effectively is crucial for creating interactive programs. You'll learn to customize output, handle user input, and convert data types to perform operations, laying the foundation for more complex programming tasks.

Input and Output Functions

Custom output with print()

• print()

  displays output to the console (stdout)
• Separates arguments with a space by default and ends with a newline character
• Customize the separator using the

  [sep](https://www.fiveableKeyTerm:sep)

  parameter

  • print("Hello", "world", sep="-")

    outputs "Hello-world"
• Customize the line ending using the

  [end](https://www.fiveableKeyTerm:end)

  parameter

  • print("Hello", end="")

    outputs "Hello" without a newline

  • print("Hello", end=" ")

    outputs "Hello " with a space instead of a newline
• Use escape characters to include special characters

  • [\n](https://www.fiveableKeyTerm:\n)

    for newline,

    [\t](https://www.fiveableKeyTerm:\t)

    for tab

  • print("Hello\nworld")

    outputs "Hello" on one line and "world" on the next

User input and variable storage

• input()

  gets input from the user via the console (stdin)
• Prompts the user to enter a value and waits for input
• Returns the user's input as a string
• Assign the result of

  input()

  to a variable to store the user's input

  • name = input("Enter your name: ")

    prompts the user and stores the input in

    name

• Provide a prompt message as an argument to guide the user
  • Displayed before the user enters their input

  • age = input("Enter your age: ")

    prompts with "Enter your age: "

Data type conversion for calculations

• User input is always returned as a string by

  input()

• Convert the input to the appropriate data type for numerical operations

  • [int](https://www.fiveableKeyTerm:int)()

    converts input to an integer

    • num = int(input("Enter a number: "))

      converts input to integer and stores in

      num

  • [float](https://www.fiveableKeyTerm:Float)()

    converts input to a floating-point number

    • price = float(input("Enter the price: "))

      converts input to float and stores in

      price

• Attempting numerical operations on strings will result in a

  [TypeError](https://www.fiveableKeyTerm:TypeError)

  • result = "10" + 5

    raises an error (cannot add string and integer)
• Handle invalid input by catching exceptions with a

  try-except

  block
  • Catch

    [ValueError](https://www.fiveableKeyTerm:ValueError)

    exceptions when converting input to numerical data types
  • Example:

    try:
        age = int(input("Enter your age: "))
    except ValueError:
        print("Invalid input. Please enter a valid integer.")
    

Advanced I/O Operations

• File I/O allows reading from and writing to files on the system
• Buffering can improve performance by reducing the number of I/O operations
• Formatting options enable precise control over output appearance