capitalization of library class names

Question

Why do collection.defaultdict and collection.OrderedDict have different capitalizations?

Is there some subtle difference that I should be a

Answer 1

defaultdict is written in C and pep8 don't apply , in the other hand OrderDict is written in python,

you can read C code norm for the C implementation of Python here : PEP 7

reference : source code python2.7

defaultdict  : Modules/_collectionsmodule.c
OrderDict : Lib/collections.py