How do I do a case insensitive string comparison in Python?

Question

What's the best way to do case insensitive string comparison in Python?

I would like to encapsulate comparison of a regular strings to a repository string using in a very simple and pythonic way. I also would like to have ability to look up values in a dict hashed by strings using regular python strings. Much obliged for advice.

Answer 1

string1 = 'Hello'
string2 = 'hello'

if string1.lower() == string2.lower():
    print "The strings are the same (case insensitive)"
else:
    print "The strings are not the same (case insensitive)"

Answer 2

The usual approach is to uppercase the strings or lower case them for the lookups and comparisons. For example:

>>> "hello".upper() == "HELLO".upper()
True
>>>

Answer 3

How about converting to lowercase first? you can use string.lower().

Answer 4

lower(string1) == lower(string2)
lower(string1) <  lower(string2)
lower(string1) >  lower(string2)

Answer 5

You could subclass the builtin "str" if you need to compare a lot and dont want to clutter your code all over with .lower()

class ci_str(str):
    def __eq__(self, other):
        return self.lower() == other.lower()

a = ci_str("Hello World")
b = ci_str("hello world")
c = ci_str("foo bar")
print a == b
print b == c

>>> 
True
False

Answer 6

Please see Ignore case in Python strings

Answer 7

def insenStringCompare(s1, s2):
    """ Method that takes two strings and returns True or False, based
        on if they are equal, regardless of case."""
    try:
        return s1.lower() == s2.lower()
    except AttributeError:
        print "Please only pass strings into this method."
        print "You passed a %s and %s" % (s1.__class__, s2.__class__)

Answer 8

What about the performance of the str.lower method? I am running a batch process against a small database (500 MB of text) and using this method for case-insensitive comparison is taking about 3 times as along as the case-sensitive comparison did.

In C there are functions for doing case-insensitive comparison which do not need to alter the strings, such as stricmp. Is there no equivalent for Python?

Answer 9

import re
re.match('what to find', 'text to search through', re.IGNORECASE) is None