This is a code in a file—

    class vector(object):

      def __init__(self, r1, r2, r3):
        self.data=[float(r1), float(r2), float(r3)]
        return

Let's say that the file is saved as vector_functions.py.

This is a code that must be executed in Python shell—

    >>> a=vector(1,2,3)
    >>> print(a.data)
    [1.0, 2.0, 3.0]

The lines that must be manually typed is prefixed by the Python REPL prompt—>>>. The ones without are the outputs.

What is not explicitly mentioned is that the reader will have to import the code before executing the instructions.

    >>> from vector_functions import vector
    >>> a=vector(1,2,3)
    >>> print(a.data)
    [1.0, 2.0, 3.0]