Solution Exercise 53 : python program which transform given a string into lowercase

Exercise 53

By using the (Exercise 51), create a python algorithm as a function that takes as input a string s and which returns the same string in lowercase without using the lower() method. You can use the chr() and ord() methods.

Solution

def toLowercase(s):
    # Based on the exercise 51 we can obtain the lists of all upercase characters and lowercase characters:
    uppercase_characters = [chr(i) for i in range(65 , 91)]
    lowercase_characters =  [chr(i) for i in range(97 , 122)]
    # then we can obtain a lowercase characters from uppercase characters by adding 32 to its ascii code
    
    # initializing the searched string
    s_lower = ""
    for x in s:
        if x in uppercase_characters:
            x = chr(ord(x) + 32)
            s_lower = s_lower + x
        else :
            s_lower = s_lower + x
            
    return s_lower
print(toLowercase("PYTHON Programming"))
# The output is : 'python programming'

In this algorithm:

1. The list [chr(i) for i in range(65 , 91)]: used to generate the list of all uppercase charachter [A, B, ..., Z]
2. The list [chr(i) for i in range(97 , 122)]: used to generate the list of all lowercase charachter [a, b, ..., z]
3. s_lower = "": is the seached string initialized to the empty string.
4. for x in s: used to iterate over all charachter in the string s.
5. Then we test if the charchter 'x' is in the uppercase_characters list: we transform it into lowercase by using the chr() and ord() method, and then we add it into the s_lower string s.
6. If the charchter 'x' is in the lowercase_characters list: we add it into the s_lower string.

Younes Derfoufi
my-courses.net