Question

I have a dictionary and using .keys() to convert into a list of keys then lower case the keys and sort the list, like this:

dictionary = list()
# covert all to lower case
for word in self._dict.keys():
  dictionary.append(word.lower())
dictionary.sort()
print dictionary[:5]

prints [u'a', u'a', u'aa', u'aa', u'aaa']

Why elements are duplicated?

UPDATE: stupid me, didn’t think of there might be lower case letters in the original dictionary… pure embarrassment

Answer 1

Because you’ve converted the keys to lower case. For example:

'AAA'.lower() == 'aaa'
True
'Aa'.lower() == 'aA'.lower()
True

So, if you had a class defined like this:

class C:
    def __init__(self):
        self.a = None
        self.A = None
        self.aA = None
        self.Aa = None
        self.AAA = None
        self.aAa = None

And then an instance of it:

>>> c = C()
>>> c.__dict__
{'a': None, 'A': None, 'aA': None, 'AAA': None, 'Aa': None, 'aAa': None}
>>> c.__dict__.keys()
['a', 'A', 'aA', 'AAA', 'Aa', 'aAa']

Converting the keys to lower case results in duplicates:

>>> sorted(key.lower() for key in c.__dict__.keys())
['a', 'a', 'aa', 'aa', 'aaa', 'aaa']