3.13 Built-In Function range: A Deeper Look

Function range also has two- and three-argument versions. As you’ve seen, range’s one-argument version produces a sequence of consecutive integers from 0 up to, but not including, the argument’s value. Function range’s two-argument version produces a sequence of consecutive integers from its first argument’s value up to, but not including, the second argument’s value, as in:

In [1]: for number in range(5, 10):
   ...:     print(number, end=' ')
   ...:
5 6 7 8 9

Function range’s three-argument version produces a sequence of integers from its first argument’s value up to, but not including, the second argument’s value, incrementing by the third argument’s value, which is known as the step:

In [2]: for number in range(0, 10, 2):
   ...:     print(number, end=' ')
   ...:
0 2 4 6 8

If the third argument is negative, the sequence progresses from the first argument’s value down to, but not including the second argument’s value, decrementing by the third argument’s value, as in:

In [3]: for number in range(10, 0, -2):
   ...:     print(number, end=' ')
   ...:
10 8 6 4 2

tick mark Self Check

  1. (True/False) Function call range(1, 10) generates the sequence 1 through 10.
    Answer: False. Function call range(1, 10) generates the sequence 1 through 9.

  2. (IPython Session) What happens if you try to print the items in range(10, 0, 2)?
    Answer: Nothing displays because the step is not negative (this is not a fatal error):

    In [1]: for number in range(10, 0, 2):
   ...:     print(number, end=' ')
   ...:
In [2]:

  3. (IPython Session) Use a for statement, range and print to display on one line the sequence of values 99 88 77 66 55 44 33 22 11 0, each separated by one space.
    Answer:

    In [3]: for number in range(99, -1, -11):
   ...:     print(number, end=' ')
   ...:
99 88 77 66 55 44 33 22 11 0

  4. (IPython Session) Use for and range to sum the even integers from 2 through 100, then display the sum.
    Answer:

    In [4]: total = 0

In [5]: for number in range(2, 101, 2):
   ...:     total += number
   ...:

In [6]: total
Out[6]: 2550
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