CodingPhiles
📦 Python Fundamentals
Module 2 · Topic 4

Input & Output Mastery

Master reading user input with input(), advanced print() usage, and all three string formatting methods.

Theory

The input() Function:

  • Always returns a string, regardless of what the user types
  • Blocks execution until user presses Enter
  • Optional prompt message: input("Enter name: ")
  • Must explicitly convert for numbers: int(input(...))

The print() Function — Advanced Usage:

  • print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)
  • sep: separator between multiple arguments
  • end: what to print at the end (default: newline)
  • file: output destination (can write to files)
  • flush: force immediate output (useful for progress indicators)

Three String Formatting Methods:

  1. f-strings (Python 3.6+, RECOMMENDED):
    f"Name: {name}, Age: {age}"

    • Can contain expressions: f"{2**10}"
    • Format specs: f"{3.14159:.2f}", f"{42:05d}"

  2. .format() method:
    "Name: {}, Age: {}".format(name, age)
    "Name: {0}, Age: {1}".format(name, age)

  3. % operator (oldest, C-style):
    "Name: %s, Age: %d" % (name, age)

Common Format Specifiers:

  • :.2f — 2 decimal places
  • :05d — zero-padded to 5 digits
  • :>10 — right-aligned in 10 chars
  • :<10 — left-aligned in 10 chars
  • :^10 — centered in 10 chars
  • :, — thousands separator
  • :% — percentage
Syntax
# Input
name = input("Enter name: ")     # Always returns str
age = int(input("Enter age: "))  # Convert to int

# Output with f-string
print(f"Hello {name}, you are {age} years old")

# Format specifiers
print(f"{price:.2f}")     # 2 decimals
print(f"{num:05d}")       # Zero-padded
print(f"{val:>10}")       # Right-aligned