Python program to generate a list of alphabets in lexical order

Prerequisite: chr()

The following methods explain how a python list with alphabets in lexical(alphabetic) order can be generated dynamically using chr() method.

Approach:

The core of the concept in both methods is almost same, they only differ in implementation:

1. Validate size of alphabet list(size=26).
2. If size>26, change to 26.
3. If size≤0, no meaning left to the function and to make it meaningful set size to 26.
4. Use chr() to produce the list using any of following methods.

Method 1: Using loop

Python3

# function to get the list of alphabets
def generateAlphabetListDynamically(size = 26):
  size = 26 if (size > 26 or size <= 0) else size

  # Empty list
  alphabetList = []

  # Looping from 0 to required size
  for i in range(size):
    alphabetList.append(chr(65 + i))

  # return the generated list
  return alphabetList


alphabetList = generateAlphabetListDynamically()
print('The alphabets in the list are:', *alphabetList)

Output:

The alphabets in the list are: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Time Complexity: O(n), where n is length of alphabetList.
Auxiliary Space: O(n), where n is length of alphabetList.

Method 2: using list comprehension

Python3

def generateAlphabetListDynamically(size=26):
    size = 26 if (size > 26 or size <= 0) else size

    # Here we are looping from 0 to upto specified size
    # 65 is added because it is ascii equivalent of 'A'
    alphabetList = [chr(i+65) for i in range(size)]

    # returning the list
    return alphabetList


# Calling the function to get the alphabets
alphabetList = generateAlphabetListDynamically()
print('The alphabets in the list are:', *alphabetList)

Output:

The alphabets in the list are: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Time Complexity: O(n)
Auxiliary Space: O(n)

Approach 3: Using the string library

This approach is simpler compared to the other two, as we don’t have to use any loop or list comprehension. Instead, we just use the string.ascii_uppercase constant, which returns a string containing all ASCII uppercase letters. Then, we just slice it to get the first size characters and convert it to a list.

Python3

import string

def generateAlphabetListDynamically(size=26):
  size = 26 if (size > 26 or size <= 0) else size
  alphabetList = list(string.ascii_uppercase[:size])
  return alphabetList
alphabetList = generateAlphabetListDynamically()
print('The alphabets in the list are:', *alphabetList)

Output

The alphabets in the list are: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Time Complexity: O(n)
Auxiliary Space: O(n)