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stdin

Short for standard input, stdin is the default input stream that a process reads to receive data, typically typed in at the keyboard.

Standard input is one of three preconnected I/O streams that a process inherits from the process that started it. The other two, standard output and standard error, work in the opposite direction and write to the screen by default, with standard error reserved for error and diagnostic messages.

The Unix model treats stdin as a plain stream of bytes, so a program reads it the same way no matter where the bytes come from. The data might be typed at the keyboard, read from a file, or piped in from another program.

This consistency is what lets you redirect input from a file with the < file syntax or chain commands into pipelines, where the shell connects stdin to the new source before the program runs. For example, you can list a directory and keep only the Python files:

Language: Shell 
$ ls | grep '\.py$'
app.py
utils.py

In that pipeline, ls writes its list of filenames to standard output, and the pipe hands those lines to grep as its standard input. Because grep reads from stdin like any other source, it filters the list down to the names ending in .py, never knowing the data came from another command.

In Python, you access standard input through sys.stdin. When you type input directly in a terminal, you signal end-of-file with Ctrl+D on Unix-like systems or Ctrl+Z on Windows.

Basic Input, Output, and String Formatting in Python

Tutorial

Basic Input and Output in Python

In this tutorial, you'll learn how to take user input from the keyboard with the input() function and display output to the console with the print() function. You'll also use readline to improve the user experience when collecting input and to effectively format output.

basics python

For additional information on related topics, take a look at the following resources:

By Martin Breuss • Updated June 10, 2026 • Reviewed by Leodanis Pozo Ramos
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