January 22, 2026 - Using .casefold() for Case-Insensitive String Comparison in Python

When you need to compare string in Python, a lot of us reach for .strip().lower() by default to pre-normalize the strings. But it turns out that .lower() doesn’t really work when you start thinking about non-ASCII characters. For example, the German letter “ß” (Eszett) should probably be equivalent to “ss” in a case-insensitive comparison, but .lower() doesn’t handle that correctly. So how can we do better? Python has a method .casefold() that is specifically designed for caseless matching of strings. It takes .lower() a step further by handling more complex cases, including those involving special characters and different alphabets:

words = [
    "HELLO",
    "Straße",      # German ß
    "İstanbul",   # Turkish dotted capital I
    "ΜΆΪΟΣ",      # Greek with accents
]

for word in words:
    print(f"Original: {word}")
    print(f"lower():    {word.lower()}")
    print(f"casefold(): {word.casefold()}")
    print("-" * 30)

# Equality comparison example
a = "Straße"
b = "strasse"

print("Comparison example:")
print("Using lower():", a.lower() == b.lower())
print("Using casefold():", a.casefold() == b.casefold())

Gives:

Original: HELLO
lower():    hello
casefold(): hello
------------------------------
Original: Straße
lower():    straße
casefold(): strasse
------------------------------
Original: İstanbul
lower():    i̇stanbul
casefold(): i̇stanbul
------------------------------
Original: ΜΆΪΟΣ
lower():    μάϊος
casefold(): μάϊοσ
------------------------------
Comparison example:
Using lower(): False
Using casefold(): True

So now you know :)