Print Operations

In Python, print prints things—it’s simply a programmer-friendly interface to the standard output stream.

Technically, printing converts one or more objects to their textual representations, adds some minor formatting, and sends the resulting text to either standard output or another file-like stream. In a bit more detail, print is strongly bound up with the notions of files and streams in Python:

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File object methods

In Chapter 9, we learned about file object methods that write text (e.g., file.write(str)). Printing operations are similar, but more focused—whereas file write methods write strings to arbitrary files, print writes objects to the stdout stream by default, with some automatic formatting added. Unlike with file methods, there is no need to convert objects to strings when using print operations.

Standard output stream

The standard output stream (often known as stdout) is simply a default place to send a program’s text output. Along with the standard input and error streams, it’s one of three data connections created when your script starts. The standard output stream is usually mapped to the window where you started your Python program, unless it’s been redirected to a file or pipe in your operating system’s shell.
Because the standard output stream is available in Python as the stdout file object in the built-in sys module (i.e., sys.stdout), it’s possible to emulate print with file write method calls. However, print is noticeably easier to use and makes it easy to print text to other files and streams.

Printing is also one of the most visible places where Python 3.0 and 2.6 have diverged. In fact, this divergence is usually the first reason that most 2.X code won’t run unchanged under 3.X. Specifically, the way you code print operations depends on which version of Python you use:

 

 
  • In Python 3.X, printing is a built-in function, with keyword arguments for special modes.
  • In Python 2.X, printing is a statement with specific syntax all its own.

Because this book covers both 3.0 and 2.6, we will look at each form in turn here. If you are fortunate enough to be able to work with code written for just one version of Python, feel free to pick the section that is relevant to you; however, as your circumstances may change, it probably won’t hurt to be familiar with both cases.