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)
range(1,20,5)

To see the list created by range you need to tell python to display the range of numbers as a list.

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

A list of things in python is easy to identify because of 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:

>>> list(range(20))
>>> list(range(10,20))
>>> list(range(10,20,2))
>>> list(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(f"{x:5d}{x**2:8d}")

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()