Python in a Nutshell

Text Input and Output

Python presents non-GUI text input and output channels to your programs as file objects, so you can use the methods of file objects (covered in Section 10.3 earlier in this chapter) to manipulate these channels.

Standard Output and Standard Error

The sys module, covered in Chapter 8, has attributes stdout and stderr, file objects to which you can write. Unless you are using some sort of shell redirection, these streams connect to the terminal in which your script is running. Nowadays, actual terminals are rare: the terminal is generally a screen window that supports text input/output (e.g., an MS-DOS Prompt console on Windows or an xterm window on Unix).

The distinction between sys.stdout and sys.stderr is a matter of convention. sys.stdout, known as your script’s standard output, is where your program emits results. sys.stderr, known as your script’s standard error, is where error messages go. Separating program results from error messages helps you use shell redirection effectively. Python respects this convention, using sys.stderr for error and warning messages.

The print Statement

Programs that output results to standard output often need to write to sys.stdout. Python’s print statement can be a convenient alternative to sys.stdout.write. The print statement has the following syntax:

print [>>fileobject,] expressions [,]

The normal destination of print’s output is the file or file-like object that is the value of the stdout attribute of the sys module. ...