Python 3 reference · Built-in Functions

Python range() Function

Create an immutable sequence of integers from start up to (but not including) stop, in steps. Used in for loops.

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Syntax

range(stop)
range(start, stop, step=1)

Parameter	Description
`start` optional	The first number. Default: `0`
`stop`	The end; this number is not included.
`step` optional	The difference between numbers; can be negative. Default: `1`

A range object (a lazy sequence; it doesn't store every number).

Start, stop and stepTry it yourself

print(list(range(5)))
print(list(range(2, 8)))
print(list(range(0, 20, 5)))
print(list(range(5, 0, -1)))

Output

[0, 1, 2, 3, 4]
[2, 3, 4, 5, 6, 7]
[0, 5, 10, 15]
[5, 4, 3, 2, 1]

Repeat something n timesTry it yourself

for i in range(3):
    print("round", i + 1)

Output

round 1
round 2
round 3

Ranges are lazy and fastTry it yourself

r = range(0, 1_000_000_000, 2)
print(len(r), r[10], 999_999_998 in r)  # no huge list is built

Output

500000000 20 True

range(1, 10) stops at 9. To include the end, use range(1, 11). To loop over a list with indexes, prefer enumerate() over range(len(items)).

Version	Change
Python 3.0	Added

enumerate() · Loop over an iterable and get each item together with its index, as (index, item) pairs. The start number is configurable.
len() · Return the number of items in a container: characters in a string, items in a list, keys in a dict, and so on.
list() · Create a list: an ordered, changeable sequence. Called with an iterable, it copies its items into a new list.
reversed() · Return an iterator that goes through a sequence backwards, without copying it. Works on lists, tuples, strings and ranges.
Python For Loops · tutorial

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