You can use dict's get() method to get back a None for missing keys instead of throwing a KeyError exception. That avoids the overhead of checking `if key in dict` or catching KeyError.
class optionaldict(defaultdict):
"""
A defaultdict that disregards KeyErrors and returns None for missing keys.
"""
def __init__(self, *original, **kwargs):
super().__init__(lambda: None, *original, **kwargs) {k: None}[k]
{}[k]