Underlying the way mappings deal with missing keys is the aptly named __missing__ method. This method is not defined in the base dict class, but dict is aware of it: if you subclass dict and provide a __missing__ method, the standard dict.__getitem__will call it whenever a key is not found, instead of raising KeyError.

StrKeyDict0.py

class StrKeyDict0(dict): 
 def __missing__(self, key):
 if isinstance(key, str): 
 raise KeyError(key)
 return self[str(key)] 
 def get(self, key, default=None):
 try:
 return self[key] 
 except KeyError:
 return default 
 def __contains__(self, key):
 return key in self.keys() or str(key) in self.keys()