What do the three arrow (">>>") signs mean?

Question

I haven't been able to figure out what the >>> does, even though I often see it often in source code.

Answer 1

You won't see it in source code, it's probably documentation. It indicates an interactive session, and things typed into the 'interpreter' are marked with this. Output is shown without the arrows.

In fact, the python documentation often has a button >>>at the top right of example code to be able to hide the arrows (and output) so that you can copy and paste the code.

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Answer 2

'>>>' is the prompt of the interactive Python interpreter, meaning that the interpreter is ready to get Python statements typed in. It's occuring quite often in examples within the documentation of a Python program, in order to show which commands can be used and what will be the result of giving these commands to the interactive interpreter. For example, in a documentation of the print statement, one could give this example:

>>> print "Hello world." Hello world. 

This would be an actual snippet of a session with the interactive Python interpreter.

An interesting feature in IPython is that it ignores leading >>>, meaning that you can copy and paste code from such documentation without needing to remove the leading >>>:

In [1]: >>> print "Hello world." Hello world. 

(The prompt in IPython is In [n]:, where n is counting the interactive commands issued.)