Python range(): Represent Numerical Ranges

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January 10, 2024
Python range(): Represent Numerical Ranges
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A range is a Python object that represents an interval of integers. Usually, the numbers are consecutive, but you can also specify that you want to space them out. You can create ranges by calling range() with one, two, or three arguments, as the following examples show:

Python 
>>> list(range(5))
[0, 1, 2, 3, 4]

>>> list(range(1, 7))
[1, 2, 3, 4, 5, 6]

>>> list(range(1, 20, 2))
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

In each example, you use list() to explicitly list the individual elements of each range. You’ll study these examples in more detail soon.

In this tutorial, you’ll learn how you can:

  • Create range objects that represent ranges of consecutive integers
  • Represent ranges of spaced-out numbers with a fixed step
  • Decide when range is a good solution for your use case
  • Avoid range in most loops

A range can sometimes be a powerful tool. However, throughout this tutorial, you’ll also explore alternatives that may work better in some situations. You can click the link below to download the code that you’ll see in this tutorial:

Construct Numerical Ranges

In Python, range() is built in. This means that you can always call range() without doing any preparations first. Calling range() constructs a range object that you can put to use. Later, you’ll see practical examples of how to use range objects.

You can provide range() with one, two, or three integer arguments. This corresponds to three different use cases:

  1. Ranges counting from zero
  2. Ranges of consecutive numbers
  3. Ranges stepping over numbers

You’ll learn how to use each of these next.

Count From Zero

When you call range() with one argument, you create a range that counts from zero and up to, but not including, the number you provided:

Python 
>>> range(5)
range(0, 5)

Here, you’ve created a range from zero to five. To see the individual elements in the range, you can use list() to convert the range to a list:

Python 
>>> list(range(5))
[0, 1, 2, 3, 4]

Inspecting range(5) shows that it contains the numbers zero, one, two, three, and four. Five itself is not a part of the range. One nice property of these ranges is that the argument, 5 in this case, is the same as the number of elements in the range.

Count From Start to Stop

You can call range() with two arguments. The first value will be the start of the range. As before, the range will count up to, but not include, the second value:

Python 
>>> range(1, 7)
range(1, 7)

The representation of a range object just shows you the arguments that you provided, so it’s not super helpful in this case. You can use list() to inspect the individual elements:

Python 
>>> list(range(1, 7))
[1, 2, 3, 4, 5, 6]

Observe that range(1, 7) starts at one and includes the consecutive numbers up to six. Seven is the limit of the range and isn’t included. You can calculate the number of elements in a range by subtracting the start value from the end value. In this example, there are 7 - 1 = 6 elements.

Count From Start to Stop While Stepping Over Numbers

Read the full article at https://realpython.com/python-range/ »

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January 10, 2024 at 07:30PM
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