pandas 足够男人/女人来解析，而无需使用格式字段:

pandas is man/woman enough to parse this without a format field:

In[90]:
pd.to_datetime('01-JUN-17 00:00:00')

Out[90]: Timestamp('2017-06-01 00:00:00')

所以这应该起作用:

df['dayofservice'] =  pd.to_datetime(df['dayofservice'])