[Tut] How to Ignore Case in Strings

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How to Ignore Case in 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.

Code:

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 a
  Code:

  lower()
  and a
  Code:

  lambda
  
  
  
• Method 2: Use
  Code:

  upper()
  and
  Code:

  List Comprehension
  
  
  
• Method 3: Use
  Code:

  title()
  
  
  
• Method 4: Use
  Code:

  casefold()
  
  
  
• Method 5: Use
  Code:

  lower()
  and Dictionary Comprehension
  
  
• Bonus: Convert CSV of Full Names to title case
  

Method 1: Use lower() and a lambda

This method uses

Code:

lower()

and a

Code:

lambda

to convert a

Code:

List

of Strings to lower case to search for an Employee.

Code:

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

Above declares a

Code:

List

of Rivers Clothing Employees. If we were searching for an Employee, such as

Code:

Darcy

, using this List, no results would return as

Code:

Darcy

and

Code:

DarCY

are not the same. Let’s fix this issue.

Info: A

Code:

l

Code:

a

Code:

mbda

function is a one-liner that, in this case, converts each List element in

Code:

staff

to lower case. Then, converts to a

Code:

map()

object and back to a https://blog.finxter.com/python-lists/List. The output saves to

Code:

staff_lower

and is output to the terminal.

Code:

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

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

Code:

if ('Darcy'.lower() == staff_lower[3]): print('Match Found!')

Match Found!



Method 2: Use upper() and List Comprehension

This method uses

Code:

upper()

and a list comprehension to convert a List of Strings to upper case and search for an Employee.

Code:

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

Code:

Channel

, using this List, no results would return as

Code:

Channel

and

Code:

ChaNnel

are not the same. Let’s fix this issue.

Ahttps://blog.finxter.com/a-simple-introd...in-python/List Comprehension is called and converts each element in

Code:

brands

to upper case. The results are saved to

Code:

brands_upper

and output to the terminal.

Code:

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

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

Code:

my_fav = 'Murad' if (my_fav.upper() == brands_upper[4]): print(f'{my_fav} Found!')

Murad Found!



Method 3: Use title()

This method uses

Code:

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.

Code:

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

Above accepts a string, appends the

Code:

title()

method to the string, saves it to

Code:

full_name

and outputs to the terminal.

Code:

Jessica A. Barker

Method 4: Use casefold() and a Dictionary

This method uses

Code:

casefold()

to convert a String to lower case. This method does more than

Code:

lower()

: it uses Unicode Case Folding Rules.

Code:

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

Above creates a quote in German and saves it to

Code:

phrase

. This ensures all characters are correctly converted to lower case, thus making a caseless match.

Code:

nichts ist unmöglich für den unwilligen!

What does this say?

Method 5: Use lower() and Dictionary Comprehension

This method uses Use

Code:

lower()

to convert Dictionary values into lower case using Dictionary Comprehension.

Code:

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

Code:

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

Code:

result

and is output to the terminal.

Code:

{'Sandy': 'coder', 'Kevin': 'network specialist', 'Amy': 'designer'}

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

Code:

title()

case. This can be accomplished by running the following code.

Contents of

Code:

finxter_users.csv

file

FID |
Full_Name

30022145 |
sally jenkins

30022192 |
joyce hamilton

30022331 |
allan thompson

30022345 |
harry stiller

30022157 |
ben hawkins

Code:

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

Code:

finxter_users.csv

file (contents shown above) is read and saved to the DataFrame

Code:

users

.

The highlighted line directly accesses all values in the

Code:

users['Full_Name']

column and converts each entry to

Code:

title()

case. This saves back to

Code:

users['Full_Name']

and is output to the terminal.

|
FID |
Full_Name

0 |
30022145 |
Sally Jenkins

1 |
30022192 |
Joyce Hamilton

2 |
30022331 |
Allan Thompson

3 |
30022345 |
Harry Stiller

4 |
30022157 |
Ben Hawkins

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



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

Code:

oct()

and

Code:

int()

Python built-in functions!)