a = {}
#a.a = 'a' #AttributeError: 'dict' object has no attribute 'a'
#a['a'] #KeyError: 'a'
a['a'] = 'a'
a #{'a': 'a'}

a = {'a': 'a'}
b = {}
#a.a #AttributeError: 'dict' object has no attribute 'a'
#a.get('a') #'a'
#b.get('b') #None
a['a'] #'a'