Case-insensitive string comparison in Python

We generally use Python lists to store items. An online shopping application may contain a list of items in it so that the user can search the item from the list of items. For example, Our shopping application has a list of laptops it sells. List contains many brands and one of them is ‘Lenovo’. If we want to buy a laptop of Lenovo brand we go to the search bar of shopping app and search for ‘Lenovo’. Then it displays all the models of Lenovo laptops. But sometimes the user may type ‘lenovo’ in lowercase or ‘LENOVO’ in upper case. Even then it should display all the models of Lenovo laptops. That means we should perform a case-insensitive check.

 Case-insensitive means the string which you are comparing should exactly be the same as a string which is to be compared but both strings can be either in upper case or lower case. (ie., different cases)

Example 1: Conversion to lower case for comparison

In this example, the user string and each list item are converted into lowercase and then the comparison is made.

Python3

# conversion to lowercase for search

#function to search item
def check_Laptops():

    laptops = ['Msi', 'Lenovo', 'Hp', 'Dell']

    your_laptop = 'lenovo'

    # 'lenovo' is in lower case but it is present in the list of laptops.

    for lapy in laptops:

      #convert to lowercase and compare
        if your_laptop.lower() == lapy.lower():

            return True

    else:

        return False

# If the function returns true
if check_Laptops():

    print('Laptop is present')


# If function returns false
else:

    print('Laptop is not present')

Output

Laptop is present

Time Complexity: O(n), where n is length of laptops list.

Auxiliary Space: O(1)

Example 2: Conversion to uppercase for comparison

In this example, the user string and each list item are converted into uppercase and then the comparison is made. 

Python3

# conversion to upper case

# Function to search item
def check_Laptops():

  laptops = ['Msi', 'Lenovo', 'Hp', 'Dell']

  your_laptop = 'HP'

  # 'HP' is in upper case but it is
  # present in the list of laptops.

  for lapy in laptops:

    # convert to uppercase and compare
      if your_laptop.upper() == lapy.upper():

          return True

  else:

      return False


if check_Laptops():

  #If the function is true
  print('Laptop is present')

else:

  #If the function returns false
  print('Laptop is not present')

Output

Laptop is present

Example 3: 

In this example, the string is not present in the list. So case-insensitive search also returns false.

Python3

# Function to search item
def check_Laptops():

  laptops = ['Msi', 'Lenovo', 'Hp', 'Dell']

  your_laptop = 'Acer'

  for lapy in laptops:

    #convert to lower and compare
      if your_laptop.lower() == lapy.lower():
          return True

  else:
      return False

if check_Laptops():

  # If the function returns false
  print('Laptop is present')

else:

  # If the function returns false
  print('Laptop is not present')

Output

Laptop is not present

Example 4:  Comparison using casefold()

The casefold() method works similar to lower() method. But compared to lower() method it performs a strict string comparison by removing all case distinctions present in the string. In German, ‘β‘ is equivalent to “ss“. But every user might not know German, so casefold() method converts German letter ‘β’ to ‘ss’ whereas we cannot convert German letter ‘β’ to ‘ss’ by using lower() method.

In this example, we are checking whether our classroom is present in the list of classrooms or not.

Python3

#initial list
classrooms=['class1','class2','CLASS3','class4','class5']

# class to be searched
class_room='claß3'

#' claß3' means 'class3'

#function to search item
def search_classroom():
   for classes in classrooms:
       if class_room.casefold()==classes.casefold():
           return True

   else:
       return False

if search_classroom():

  # If function returns true
   print('Classroom you are searching is present')

else:

  # If function returns false
   print('Classroom you are searching is not present')

Output

Classroom you are searching is present

These are the methods in Python for case-insensitive string comparison.