Python create list from range

The range[] method returns an immutable sequence of numbers between the given start integer to the stop integer.

Example

print[list[range[6]]] # Output: [0, 1, 2, 3, 4, 5]

range[] constructor has two forms of definition:

range[stop] range[start, stop[, step]]

range[] Parameters

range[] takes mainly three arguments having the same use in both definitions:

• start - integer starting from which the sequence of integers is to be returned
• stop - integer before which the sequence of integers is to be returned.
  The range of integers ends at stop - 1.
• step [Optional] - integer value which determines the increment between each integer in the sequence

range[] Return value

range[] returns an immutable sequence object of numbers depending upon the definitions used:

range[stop]

• Returns a sequence of numbers starting from 0 to stop - 1
• Returns an empty sequence if stop is negative or 0.

range[start, stop[, step]]

The return value is calculated by the following formula with the given constraints:

r[n] = start + step*n [for both positive and negative step] where, n >=0 and r[n] < stop [for positive step] where, n >= 0 and r[n] > stop [for negative step]

• [If no step] Step defaults to 1. Returns a sequence of numbers starting from start and ending at stop - 1.
• [if step is zero] Raises a ValueError exception
• [if step is non-zero] Checks if the value constraint is met and returns a sequence according to the formula
  If it doesn't meet the value constraint, Empty sequence is returned.

Example 1: How range works in Python?

# empty range print[list[range[0]]] # using range[stop] print[list[range[10]]] # using range[start, stop]

print[list[range[1, 10]]]

Output

[] [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] [1, 2, 3, 4, 5, 6, 7, 8, 9]

Note: We've converted the range to a Python list, as range[] returns a generator-like object that only prints the output on demand.

However, the range object returned by the range constructor can also be accessed by its index. It supports both positive and negative indices.

You can access the range object by index as:

rangeObject[index]

Example 2: Create a list of even number between the given numbers using range[]

start = 2 stop = 14 step = 2

print[list[range[start, stop, step]]]

Output

[2, 4, 6, 8, 10, 12]

Example 3: How range[] works with negative step?

start = 2 stop = -14 step = -2

print[list[range[start, stop, step]]]

# value constraint not met print[list[range[start, 14, step]]]

Output

[2, 0, -2, -4, -6, -8, -10, -12] []

PythonServer Side ProgrammingProgramming

Python can handle any requirement in data manipulation through its wide variety of libraries and methods. When we need to generate all the numbers between a pair of given numbers, we can use python’s inbuilt functions as well as some of the libraries. This article describes such approaches.

Using range

The range[] function returns a sequence of numbers, starting from 0 by default, and increments by 1 ending at a specified number. We can of curse change the starting, ending as well as increment steps to suit our need.

Example

 Live Demo

def getnums[s, e,i]:    return list[range[s, e,i]] # Driver Code start, end, intval = -3, 6,2 print[getnums[start, end,intval]]

Output

Running the above code gives us the following result −

[-3, -1, 1, 3, 5]

Using randrange

The random module can also generate a random number between in a similar way as above. It involves calling the randrange method and supplying the parameters for start, end and interval values.

Example

 Live Demo

import random def getnums[s, e,i]:    return [random.randrange[s, e,i]] # Driver Code start, end, intval = 3, 16,2 print[getnums[start, end,intval]]

Output

Running the above code gives us the following result −

7

With numpy.arrange

The numpy library also provides a very wide range of functions for these requirements. We use arrange function which will also take the required parameters and give the output as a list.

Example

 Live Demo

import numpy as np def getnums[s, e,i]:    return [np.arange[s, e,i]] # Driver Code start, end, intval = 3, 16,2 print[getnums[start, end,intval]]

Output

Running the above code gives us the following result −

[ 3 5 7 9 11 13 15]

Published on 04-May-2020 12:57:48

Examples of how to create a list of numbers in python using list comprehensions or built-in functions list[]:

Create a list of integers

To create a list of integers between 0 and N, a solution is to use the range[N] function:

>>> l = [i for i in range[10]] >>> l [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> l = list[range[10]] >>> l [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

To create a list of integers between N and M [with M>N], the function range[] can still be used:

>>> l = [i for i in range[25,35]] >>> l [25, 26, 27, 28, 29, 30, 31, 32, 33, 34] >>> l = list[range[25,35]] >>> l [25, 26, 27, 28, 29, 30, 31, 32, 33, 34]

Create a list of floats using arange

To create a list of floats between [N,M] with a given step, a solution is to use the numpy function called arange:

>>> import numpy as np >>> l = [i for i in np.arange[2,8,0.5]] >>> l [2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5] >>> l = list[np.arange[2,8,0.5]] >>> l [2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5]

Create a list of floats using linspace

To create a list of floats between [N,M] with a given number of elementsa solution is to use the numpy function linspace:

>>> import numpy as np >>> l = [i for i in np.linspace[12,16,8]] >>> l [12.0, 12.571428571428571, 13.142857142857142, 13.714285714285714, 14.285714285714285, 14.857142857142858, 15.428571428571429, 16.0] >>> l = list[np.linspace[12,16,8]] >>> l [12.0, 12.571428571428571, 13.142857142857142, 13.714285714285714, 14.285714285714285, 14.857142857142858, 15.428571428571429, 16.0]

Create a list of random integers

The python function randint can be used to generate a random integer in a chosen interval [a,b]:

>>> import random >>> random.randint[0,10] 7 >>> random.randint[0,10] 0

A list of random numbers can be then created using python list comprehension approach:

>>> l = [random.randint[0,10] for i in range[5]] >>> l [4, 9, 8, 4, 5]

Another solution is to use randrange function [except that can specify a step if you need]:

>>> l = [random.randrange[0,10] for i in range[5]] >>> l [1, 7, 4, 3, 1] >>> l = [random.randrange[0,10,2] for i in range[5]] >>> l [2, 4, 4, 6, 0]

A third solution is to create a list of random numbers with no repetition, is to use random.sample function

>>> l = random.sample[range[1,100], 10] >>> l [89, 56, 87, 51, 46, 25, 52, 44, 10, 32]

References

In Pythons >> r = range[10] >>> l = [*r] >>> print[l] [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Though this is equivalent to list[r], it's literal syntax and the fact that no function call is involved does let it execute faster. It's also less characters, if you need to code golf :-]