Reading Input

Intuition

print sends text out; input brings text in. When a program reaches input() it waits for one line from the keyboard (or from whatever is connected to standard input, such as a file or an automatic grader) and gives it to you as a string.

Precise explanation

name = input()                 # one line, without the trailing newline, always a str
year = int(input())            # convert when you need a number
city = input("City? ")         # an optional prompt is printed first (not used in graded tasks)
  • input() returns a str, even if the user typed digits. input() + 1 is a TypeError.
  • text.strip() removes spaces, tabs and newlines from both ends. int() and float() already ignore surrounding whitespace, but names and words do not.
  • Each call reads the next line. If there is no line left, Python raises EOFError.

Worked example

Input:

  Grace
1990

name = input().strip()     # "Grace"
birth_year = int(input())  # 1990
print(f"Hello, {name}! In 2030 you will turn {2030 - birth_year}.")

Output: Hello, Grace! In 2030 you will turn 40.

Common mistakes

  • Forgetting int(...), then subtracting a string.
  • Printing a prompt in graded tasks: the prompt becomes part of your output and breaks exact comparisons. Tests in this site supply input directly, so call input() with no prompt.
  • Calling input() more times than there are lines.

Why this matters

Reading and validating outside data is where most real programs start: command-line tools, web forms (FA-01 later) and dataset files all deliver text you must parse.

References