How to Ignore Case in Python Strings

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Problem Formulation and Solution Overview

In this article, you’ll learn how to ignore (upper/lower/title) case characters when dealing with Strings in Python.

The main reason for ignoring the case of a String is to perform accurate String comparisons or to return accurate search results.

For example, the following three (3) Strings are not identical. If compared with each other, they would return False.

when life gives you lemons, make lemonade.
WHEN LIFE GIVES YOU LEMONS, MAKE LEMONADE.
When Life Gives You Lemons, Make Lemonade.

This is because each character in the ASCII Table assigns different numeric values for each key or key combination on the keyboard.

This article outlines various ways to ignore the case of Strings.


💬 Question: How would we write code to compare Strings?

We can accomplish this task by one of the following options:


Method 1: Use lower() and a lambda

This method uses lower() and a lambda to convert a List of Strings to lower case to search for an Employee.

staff = ['Andy', 'MAci', 'SteVe', 'DarCY', 'Harvey']
staff_lower = list((map(lambda x: x.lower(), staff)))
print(staff_lower)

Above declares a List of Rivers Clothing Employees. If we were searching for an Employee, such as Darcy, using this List, no results would return as Darcy and DarCY are not the same. Let’s fix this issue.

ℹ️ Info: A lambda function is a one-liner that, in this case, converts each List element in staff to lower case. Then, converts to a map() object and back to a List. The output saves to staff_lower and is output to the terminal.

['andy', 'maci', 'steve', 'darcy', 'harvey']

If a comparison was made now, it would find the correct Employee.

if ('Darcy'.lower() == staff_lower[3]):
    print('Match Found!')
Match Found!
Let's Play Finxter - The Lambda Function in Python

Method 2: Use upper() and List Comprehension

This method uses upper() and a list comprehension to convert a List of Strings to upper case and search for an Employee.

brands = ['ChaNnel', 'CLINique', 'DIOR', 'Lancome', 'MurAD']
brands_upper = [x.upper() for x in brands]
print(brands_upper)

Above declares a List of the Top five (5) Beauty Brands in the world. If we were searching for a Company, such as Channel, using this List, no results would return as Channel and ChaNnel are not the same. Let’s fix this issue.

A List Comprehension is called and converts each element in brands to upper case. The results are saved to brands_upper and output to the terminal.

['CHANEL', 'CLINIQUE', 'DIOR', 'LANCOME', 'MURAD']

If a comparison was made now, it would find the correct Brand.

my_fav = 'Murad'
if (my_fav.upper() == brands_upper[4]):
    print(f'{my_fav} Found!')
Murad Found!
Python One-Liner Trick 9 - Nested List Comprehension

Method 3: Use title()

This method uses title() to convert each word in a String to upper case. Great use of this is to convert a Full Name to title case. This ensures both the First, Middle and Last Names are as expected.

full_name = 'jessica a. barker'.title()
print(full_name)

Above accepts a string, appends the title() method to the string, saves it to full_name and outputs to the terminal.

Jessica A. Barker
Python String Methods [Ultimate Guide]

Method 4: Use casefold() and a Dictionary

This method uses casefold() to convert a String to lower case. This method does more than lower(): it uses Unicode Case Folding Rules.

phrase = 'Nichts ist unmöglich für den Unwilligen!'
cfold = phrase.casefold()
print(cfold)

Above creates a quote in German and saves it to phrase. This ensures all characters are correctly converted to lower case, thus making a caseless match.

nichts ist unmöglich für den unwilligen!

What does this say?


Method 5: Use lower() and Dictionary Comprehension

This method uses Use lower() to convert Dictionary values into lower case using Dictionary Comprehension.

employees = {'Sandy': 'Coder', 'Kevin': 'Network Specialist', 'Amy': 'Designer'}
result = {k: v.lower() for k, v in employees.items()}
print(result)

Above creates a Dictionary containing Rivers Employees Names and associated Job Title. This saves to employees.

Next, Dictionary Comprehension is used to loop through the values in the key:value Dictionary pairs and convert the values to lower case. The output saves to result and is output to the terminal.

{'Sandy': 'coder', 'Kevin': 'network specialist', 'Amy': 'designer'}
Python Dictionary Comprehension - A Powerful One-Liner Tutorial

Bonus: CSV Column to title() case

In this Bonus section, a CSV file you are working with contains a column of Full Names. You want to ensure all data entered in this column is in title() case. This can be accomplished by running the following code.

Contents of finxter_users.csv file

FID Full_Name
30022145sally jenkins
30022192joyce hamilton
30022331allan thompson
30022345harry stiller
30022157ben hawkins
import pandas as pd 
users = pd.read_csv('finxter_users.csv')
users['Full_Name'] = users['Full_Name'].str.title()
print(users)

Above imports the Pandas library. For installation instructions, click here.

Next, the finxter_users.csv file (contents shown above) is read and saved to the DataFrame users.

The highlighted line directly accesses all values in the users['Full_Name'] column and converts each entry to title() case. This saves back to users['Full_Name'] and is output to the terminal.

FID Full_Name
030022145Sally Jenkins
130022192Joyce Hamilton
230022331Allan Thompson
330022345Harry Stiller
430022157Ben Hawkins

💡Note: Don’t forget to save the DataFrame to keep the changes.

10 Minutes to Pandas in 5 Minutes (Okay 8)

Summary

These six (6) methods of ignoring cases in Strings should give you enough information to select the best one for your coding requirements.

Programmer Humor

Question: Why do programmers always mix up Halloween and Christmas?
Answer: Because Oct 31 equals Dec 25.

(If you didn’t get this, read our articles on the oct() and int() Python built-in functions!)