我希望实现__missing__（与dict中相同的行为），而不会覆盖__getitem__的子类pandas.DataFrame。这是我到目前为止所尝试的：
import pandas as pd
class Bar0(pd.DataFrame):
@property
def _constructor(self):
return Bar0
def __missing__(self, key):
print('Call __missing__ from {} with key'.format(type(self), key))
return key
class Bar1(Bar0):
@property
def _constructor(self):
return Bar1
def __getitem__(self, key):
print('Call __getitem__ from {} with key {}'.format(type(self), key))
try:
return super().__getitem__(key)
except KeyError:
return self.__missing__(key)
class Bar2(dict, Bar0):
@property
def _constructor(self):
return Bar2
def __init__(self, *args, **kwargs):
Bar0.__init__(self, *args, **kwargs)
dict.__init__(self)
self.__getitem__ = Bar0.__getitem__
class Bar3(Bar0, dict):
@property
def _constructor(self):
return Bar3
def __init__(self, *args, **kwargs):
Bar0.__init__(self, *args, **kwargs)
dict.__init__(self)
self.__getitem__ = Bar0.__getitem__
for bar in (Bar0, Bar1, Bar2, Bar3):
foo = bar({'a': [1]})
foo['a']
try:
foo['b']
except KeyError:
print('Raised KeyError for {}'.format(type(foo)))
print('')
导致：
Raised KeyError for <class '__main__.Bar0'> // Didn't call __missing__
Call __getitem__ from <class '__main__.Bar1'> with key a
Call __getitem__ from <class '__main__.Bar1'> with key b // Did call __missing__ but also __getitem__
Call __missing__ from <class '__main__.Bar1'> with key
Call __missing__ from <class '__main__.Bar2'> with key // Didn't even find 'a' - I guess it searches __getitem__ from dict instead of pd.DataFrame
Call __missing__ from <class '__main__.Bar2'> with key
Raised KeyError for <class '__main__.Bar3'> // Didn't call __missing__
对于这个案件很重要：