Python: range function

‘range()’ function is used to iterate over a sequence of numbers.

There are two variants of range function.

class range(stop)

class range(start, stop[, step])

All the arguments to range function are integers. By default start is assigned to 0, step is assigned to 1. ‘range(5) is same as ‘range(0, 5).

test.py

for i in range(5):
 print(i)

$ python3 test.py

0

1

2

3

4

test.py

for i in range(0, 15, 3):
 print(i)

$ python3 test.py

0

3

6

9

12

If you assign 0 to the argument ‘step’ then ValueError thrown.

test.py

for i in range(0, 15, 0):
 print(i)

$ python3 test.py

Traceback (most recent call last):

  File "test.py", line 1, in <module>

    for i in range(0, 15, 0):

ValueError: range() arg 3 must not be zero

test.py

for i in range(0, -10, -2):
 print(i)

$ python3 test.py

0

-2

-4

-6

-8

Check for a value in given range

By using ‘in’ operator you can check, whether given value is in range or not.

>>> 2 in range(0, 10, 2)
True
>>> 4 in range(0, 10, 2)
True
>>> 14 in range(0, 10, 2)
False
>>> 1 in range(0, 10, 2)
False

By using range(), len() functions, you can iterate over a sequence.

test.py

names=["Phalgun", "Sambith", "Mahesh", "swapna"]

for i in range(len(names)):
 print(i, names[i])
else:
 print("Exiting from loop")

print("Execution finished")

$ python3 test.py

0 Phalgun

1 Sambith

2 Mahesh

3 swapna

Exiting from loop

Execution finished

Note:

For a positive step, the contents of a range r are determined by the formula r[i] = start + step*i where i >= 0 and r[i] < stop.

For a negative step, the contents of the range are still determined by the formula r[i] = start + step*i, but the constraints are i >= 0 and r[i] > stop.

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