Python range() Function Tutorial

The range() function is a very popular and widely used function in Python, especially when you are working with for loops, and sometimes also with while loops. The range() function is worth knowing and mastering because doing so will open a lot of doors: range() is used in everything from controlling the flow of a program to looping through data sets that you are using for data analysis. 

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What is the range() Function in Python?

The range() function returns a sequence of numbers and is immutable, meaning its value is fixed. The range() function takes one or at most three arguments, namely the start and a stop value along with a step size.

range() was introduced in Python3. In Python2, a similar function, xrange(), was used, which had somewhat different behavior. Among other things, xrange() returned a generator object and consumed less memory, while range(), on the other hand, returns a list or sequence of numbers.

Part of the reason the range() function is useful is because it only stores the start, stop, and step values, so it consumes less memory when compared to a list or tuple.

Python range() Function Syntax

The range() function can be represented in three different ways, or you can think of them as three range() parameters:

• range(stop_value): By default, the starting point here is zero.

• range(start_value, stop_value): This generates the sequence based on the start and stop value.

• range(start_value, stop_value, step_size): It generates the sequence by incrementing the start value using the step size until it reaches the stop value.

We can also check the type of the range() function by wrapping range() in type().

my_range = range(100)
print(type(my_range))

# Expected output: <class 'range'>

Python range() Function Examples

Let's now take a look at a few examples so you can practice and master using range().

Using Python range() to print a sequence of numbers

Let's start with a simple example of printing a sequence of ten numbers, which will cover your first range() parameter. To achieve this, you will be just passing in the stop value. Since Python works on zero-based indexing, hence, the sequence will start with zero and stop at the specified number, i.e., n-1, where n is the specified number in the range() function.

my_range = range(10)

for num in my_range:
	print(num)

# Expected output:
# 0
# 1
# 2
# 3
# 4
# 5
# 6
# 7
# 8
# 9

As expected, the above cell returns a sequence of numbers starting with 0 and ending at 9.

Using Python range() with list()

You could also use the range function as an argument to a list in which case it would result in a list of numbers with a length equal to the stop value as shown below:

my_range = list(range(10))
print(my_range)

range_length = len(my_range)
print(range_length)

# Expected output:
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
# 10

Making use of start, stop, and step in Python range()

Next, let's look another way of working with the range() function. Here you will specify both start and the stop value.

my_range = range(5, 10)
print(my_range)

# Expected output: range(5, 10)

for num in range(5,10):
    print(num)

# Expected output:
# 5
# 6
# 7
# 8
# 9

Similarly, you can use the range() function to print the negative integer values as well.

for num in range(-5,0):
    print(num)

# Expected output:
# -5
# -4
# -3
# -2
# -1

Let's now add the third parameter, i.e., the step size to the range() function, and find out how it affects the output. You will specify the start point as 50, the stop value as 1000 with a step size of 100. The below range function should output a sequence starting from 50 incrementing with a step of 100.

my_range = range(50,1000,100)
print(my_range)

# Expected output: range(50, 1000, 100)

You will notice that it will print all even numbers.

for num in range(50,1000,100):
    print(num)

# Expected output:
# 50
# 150
# 250
# 350
# 450
# 550
# 650
# 750
# 850
# 950

A note on Python range() and float values

It is important to note that the range() function can only work when the specified value is an integer or a whole number. It does not support the float data type and the string data type. However, you can pass in both positive and negative integer values to it. Let's see what happens when you try to pass float values.

for num in range(0.2,2.4):
    print(num)

# Expected output:
# TypeError: 'float' object cannot be interpreted as an integer

You would have scratched your head at least once while trying to reverse a linked list of integer values in C language. However, in Python, it can be achieved with the range() function with just interchanging the start and stop along with adding a negative step size. Isn't that so simple? Let's find out!

for num in range(100,10,-10):
    print(num)

# Expected output:
# 100
# 90
# 80
# 70
# 60
# 50
# 40
# 30
# 20

Using range() to find the sum of a list

Say you have a list of integer values, and you would like to find the sum of the list, but using the range() function. Let's find out it can be done.

First, you will define the list consisting of integer values. Then initialize a counter in which you will store the value each time you iterate over the list and also add the current list value with the old count value.

To access the elements from the list, you will apply the range() function on the length of the list and then access the list elements bypassing the index i which will start from zero and stop at the length of the list.

list1 = [2,4,6,8,10,12,14,16,18,20]
count = 0

for i in range(len(list1)):
    count = count + list1[i]
    print(count)
print('sum of the list:', count)

# Expected output:
# 2
# 6
# 12
# 20
# 30
# 42
# 56
# 72
# 90
# 110
# sum of the list: 110

Using range() with itertools to concatenate a list

You could also concatenate two or more range() functions using the itertools package class called chain. And not just the range function, you could even concatenate list, tuples, etc. Remember that chain method returns a generator object, and to access the elements from that generator object, you can either use a for loop or use list and pass the generator object as an argument to it.

from itertools import chain

a1 = range(10,0,-2)
a2 = range(30,20,-2)
a3 = range(50,40,-2)

final = chain(a1,a2,a3)

print(final) #generator object

# Expected output: <itertools.chain object at 0xae6330>

print(list(final))

# Expected output:
# [10, 8, 6, 4, 2, 30, 28, 26, 24, 22, 50, 48, 46, 44, 42]

Python range() and equality comparisons

You can apply equality comparisons between range() functions. Given two range() functions, if they represent the same sequence of values, then they are considered to be equal. Having said that, two equal range() functions don't need to have the same start, stop, and step attributes. Let's understand it with an example.

# range(0, 10, 3) = [0, 3, 6, 9]
# range(0, 11, 3) = [0, 3, 6, 9]

print(range(0, 10, 3) == range(0, 11, 3))

# Expected output: True

# range(0, 10, 3) = [0, 3, 6, 9]
# range(0, 11, 2) = [0, 2, 4, 6, 8, 10]

print(range(0, 10, 3) == range(0, 11, 2))

# Expected output: False

As you can observe from the above outputs, even though the parameters of the range() function are different, they are still considered to be equal since the sequence of both the functions are the same. In the second example, changing the step size makes the comparison False.

Conclusion

Congratulations on finishing the tutorial. You might want to tinker around a bit with the range() function and find a way to customize it for accepting data types other than just integers.

If, after reading, you feel like could benefit from practicing Python functions, check out our Python Functions and our Beginner's Guide to Python for Loops tutorials. For a structured learning path, take a look at our Writing Efficient Python Code DataCamp course, which not only covers the range() function in detail but also helps with more general coding concepts to help you write really efficient code without a lot of overhead.