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Basic Syntax

Input and Output

print() and input() functions

Interview: Basic I/O operations

Last Updated: June 12, 2026 • 6 min read

Python provides built-in functions for console I/O: print() for output and input() for reading user input. For file I/O, see the File Handling chapter.

print() Function

The print() function writes to sys.stdout. It's more powerful than most beginners realize.

  • sep parameter: separator between values (default: space)
  • end parameter: appended after last value (default: newline)
  • file parameter: redirect output to any file-like object
  • flush parameter: force immediate output (useful for progress indicators)

input() Function

input() reads a line from stdin and returns it as a string. Always convert the result if you need a number.

Formatted Output

  • f-strings (best): f"{name} is {age}" — supports expressions, method calls, format specs
  • format(): "{0} is {1}".format(name, age)
  • % formatting: "%s is %d" % (name, age) — legacy style

String Formatting Specifiers

  • {value:.2f} — 2 decimal places
  • {value:>10} — right-align in 10 chars
  • {value:,} — thousands separator: 1,234,567
  • {value:.0%} — percentage: 75%
  • {value:08b} — binary: 00001010

Use Cases

Building CLI tools with formatted output

Reading and validating user input in interactive programs

Redirecting output to files or stderr for logging

Progress indicators with flush and carriage return

Common Mistakes

Forgetting that input() always returns a string

Not handling ValueError when converting user input to numbers

Using print() for logging instead of the logging module

Forgetting to use flush=True for real-time progress output