Python | Create list of numbers with given range

Given two numbers r1 and r2 (which defines the range), write a Python program to create a list with the given range (inclusive).

Examples:

Input : r1 = -1, r2 = 1
Output : [-1, 0, 1]

Input : r1 = 5, r2 = 9
Output : [5, 6, 7, 8, 9]

Let’s discuss a few approaches to do this task.

Approach #1 : Naive Approach

A naive method to create list within a given range is to first create an empty list and append successor of each integer in every iteration of for loop.

# Python3 Program to Create list  
# with integers within given range  
  
def createList(r1, r2): 
  
    # Testing if range r1 and r2  
    # are equal 
    if (r1 == r2): 
        return r1 
  
    else: 
  
        # Create empty list 
        res = [] 
  
        # loop to append successors to  
        # list until r2 is reached. 
        while(r1 < r2+1 ): 
              
            res.append(r1) 
            r1 += 1
        return res 
      
# Driver Code 
r1, r2 = -1, 1
print(createList(r1, r2)) 

Output:

[-1, 0, 1]

Approach #2 : List comprehension

We can also use list comprehension for the purpose. Just iterate ‘item’ in a for loop from r1 to r2 and return all ‘item’ as list. This will be a simple one liner code.

# Python3 Program to Create list  
# with integers within given range  
  
def createList(r1, r2): 
    return [item for item in range(r1, r2+1)] 
      
# Driver Code 
r1, r2 = -1, 1
print(createList(r1, r2)) 

Output:

[-1, 0, 1]

Approach #3 : using Python range()

Python comes with a direct function range() which creates a sequence of numbers from start to stop values and print each item in the sequence. We use range() with r1 and r2 and then convert the sequence into list.

# Python3 Program to Create list  
# with integers within given range  
  
def createList(r1, r2): 
    return list(range(r1, r2+1)) 
      
# Driver Code 
r1, r2 = -1, 1
print(createList(r1, r2)) 

Output:

[-1, 0, 1]

Approach #4 : Using numpy.arange()

Python numpy.arange() returns a list with evenly spaced elements as per the interval. Here we set the interval as 1 according to our need to get the desired output.

# Python3 Program to Create list  
# with integers within given range  
import numpy as np 
def createList(r1, r2): 
    return np.arange(r1, r2+1, 1) 
      
# Driver Code 
r1, r2 = -1, 1
print(createList(r1, r2)) 

Output:

[-1  0  1]

My Personal Notes

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