How to use range() in Python | note.nkmk.me (2024)

In Python, you can generate a series of integers with the built-in range() function.

• Built-in Functions - range() — Python 3.11.3 documentation

See the following article for details of for loops in Python.

• Python for loop (with range, enumerate, zip, and more)

range() and the range type in Python3

In Python3, range() creates an object of range type.

• Built-in Types - Ranges — Python 3.11.3 documentation

An object of range type does not store values, but creates them when needed. Therefore, its values are not displayed with print(). However, since it is an iterable object, its values can be printed in a for loop.

print(range(3))# range(0, 3)print(type(range(3)))# <class 'range'>for i in range(3): print(i)# 0# 1# 2

Note that Python2 has range() and xrange(), and the behavior of range() is different between Python2 and Python3. This will be explained at the end of this article.

Convert a range object to a list

If you want to convert a range object to a list, use the list() function.

print(list(range(3)))# [0, 1, 2]

In the following sample code, the result of range() is converted into a list using list(). Note that this conversion is for explanatory purposes only, and using list() is not required when working with a for loop.

range(stop): 0 <= x < stop

range(stop) generates a series of integers 0 <= i < stop. Note that stop is not included in the result.

print(list(range(3)))# [0, 1, 2]print(list(range(10)))# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Specifying a negative value returns an empty range.

print(list(range(-3)))# []

range(start, stop): start <= x < stop

range(start, stop) generates a series of integers start <= i < stop. Note that start is included, but stop is not included in the result.

The result will be empty when stop <= start.

print(list(range(3, 10)))# [3, 4, 5, 6, 7, 8, 9]print(list(range(10, 3)))# []print(list(range(-3, 3)))# [-3, -2, -1, 0, 1, 2]print(list(range(3, -3)))# []

range(0, stop) is equivalent to range(stop).

print(range(0, 3) == range(3))# True

range(start, stop, step): start <= x < stop (increasing by step)

range(start, stop, step) generates a series of integers start <= i < stop, increasing by step.

If you provide a negative value for the step argument, the sequence will decrease. In such cases, the sequence will be empty if start <= stop.

print(list(range(3, 10, 2)))# [3, 5, 7, 9]print(list(range(10, 3, 2)))# []print(list(range(10, 3, -2)))# [10, 8, 6, 4]print(list(range(3, 10, -2)))# []

range(start, stop, 1) is equivalent to range(start, stop).

print(range(3, 10, 1) == range(3, 10))# True

range(0, stop, 1) is equivalent to range(0, stop) and range(stop).

print(range(0, 10, 1) == range(0, 10) == range(10))# True

Reversed range()

Specifying a negative value for the third argument step can generate decreasing integers.

print(list(range(3, 10, 2)))# [3, 5, 7, 9]print(list(range(9, 2, -2)))# [9, 7, 5, 3]

It is also possible to use the built-in reversed() function to reverse the result of range().

• Reverse a list, string, tuple in Python (reverse, reversed)

print(list(reversed(range(3, 10, 2))))# [9, 7, 5, 3]

Also, in this case, you don't need to convert the result to a list if you use the reversed range in a for loop.

for i in reversed(range(3, 10, 2)): print(i)# 9# 7# 5# 3

range() with float

Like the previous examples, you can only specify integers (int) as the arguments to range().

An error occurs when the floating point number (float) is specified.

# print(list(range(0.3, 1.0, 0.2)))# TypeError: 'float' object cannot be interpreted as an integer

If you want to generate a series of float values, use list comprehensions.

• List comprehensions in Python

print([i / 10 for i in range(3, 10, 2)])# [0.3, 0.5, 0.7, 0.9]

A small error may occur when multiplying floating point numbers. You can round the result using the round() function.

• Round numbers with round() and Decimal.quantize() in Python

print([i * 0.1 for i in range(3, 10, 2)])# [0.30000000000000004, 0.5, 0.7000000000000001, 0.9]print([round(i * 0.1, 1) for i in range(3, 10, 2)])# [0.3, 0.5, 0.7, 0.9]

If you can use NumPy, using np.arange() is more convenient. The arguments for np.arange() are the same as for range(), with the added support for float values.

import numpy as npprint(np.arange(3))# [0 1 2]print(np.arange(3, 10))# [3 4 5 6 7 8 9]print(np.arange(3, 10, 2))# [3 5 7 9]print(np.arange(0.3, 1.0, 0.2))# [0.3 0.5 0.7 0.9]

See the following articles for np.arange() and conversion between numpy.ndarray and list.

• numpy.arange(), linspace(): Generate ndarray with evenly spaced values
• Convert numpy.ndarray and list to each other

range() and xrange() in Python2

Python2 includes two functions: range() and xrange(). In Python3, xrange() has been removed, leaving only range().

There is a difference between range() in Python2 and Python3. Note that an error may occur if code written for Python2 is executed without modification in Python3.

range() returns a list, and xrange() returns an object of type xrange.

print(range(3))# [0, 1, 2]print(type(range(3)))# <type 'list'>print(xrange(3))# xrange(3)print(type(xrange(3)))# <type 'xrange'>

The xrange() and xrange types in Python2 are equivalent to the range() and range types in Python3.

• 2. Built-in Functions - xrange() — Python 2.7.18 documentation

If you want to run old Python2 code in Python3, you need to change xrange() to range().

In Python2, range() returns a list, which is equivalent to using list(range()) in Python3. When using range() in a for loop, you don't need to use list(). However, if you want to treat the result of range() as a list, you will need to convert it using list().