最近在做GitHut上的Harvard-cs109，遇到一个地方疯狂报错，求老司机指指路（右边是链接）
以下是报错的地方：
errors = all_error_data()
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-18-aea6d425eefd> in <module>()
----> 1 errors = all_error_data()
<ipython-input-17-2a9c686164e8> in all_error_data()
17 #your code here
18 def all_error_data():
---> 19 data = [error_data(race_page) for race_page in find_governor_races(page)]
20 return pd.concat(data, ignore_index=True)
<ipython-input-14-5c576ec1e316> in error_data(url)
48 #compute forecast length in days
49 #(assuming that last forecast happens on the day of the election, for simplicity)
---> 50 forecast_length = (df.date.max() - df.date).values
51 forecast_length = forecast_length / np.timedelta64(1, 'D') # convert to number of days
52
//anaconda/lib/python2.7/site-packages/pandas/core/generic.pyc in __getattr__(self, name)
2667 if name in self._info_axis:
2668 return self[name]
-> 2669 return object.__getattribute__(self, name)
2670
2671 def __setattr__(self, name, value):
AttributeError: 'DataFrame' object has no attribute 'date'