A list-creating function: `range()`

The built-in function range creates arithmetic lists, and is often used to produce the lists to drive for loops.

range(start_value, stop_value, stepsize)

Example:

>>> range(1, 20, 5)
[1, 6, 11, 16]

You can tell that the value range returns is a list by the square brackets and the commas.

Notes:

the start_value defaults to 0.
the stepsize defaults to 1.
the stop_value is NOT included in the list. This means that the range is asymmetric: because the starting value is included, but the stopping value is not included.

Try entering the following expressions in the Python shell and see what results:

>>> range(20)
>>> range(10,20)
>>> range(10,20,2)
>>> range(20,2)

(Do you understand why the last one returns the value it does?)

Here's a little code snippet showing how range can be used to display the squares of the numbers from 1 to 10.,

print "Table of squares for 1-10"
print "    x    x**2"
for x in range(1,11):
    print "%5d%8d", % (x, x**2)

Note that since the stop value is NOT included in the list we have to specify a stop value of 11 to include the value 10.

A list-creating function: range()