python - 捕获异常并返回空数据帧

Question

我查询数据库并将结果保存为数据框，然后我通过 factorize 和 pivot_table 对其进行转换。这在数据库查询返回数据时工作正常，但在没有返回数据时抛出错误(这是预料之中的)。如何捕获此异常并返回空数据框？

#When dataframe is non-empty, transformation works fine:
print df

   sale name  year
0   41  Jason  2012
1   24  Molly  2012
2   31  Jason  2013
3   32  Jason  2014
4   31  Molly  2014


df['groups'] = (pd.factorize(df.year)[0] + 1).astype(str)

df1 = (df.pivot_table(index='name', columns='groups', values=['sale', 'year']))
df1.columns = [''.join(col) for col in df1.columns]
print (df1)

       sale1  sale2  sale3   year1   year2   year3
name                                              
Jason   41.0   31.0   32.0  2012.0  2013.0  2014.0
Molly   24.0    NaN   31.0  2012.0     NaN  2014.0

#But when dataframe is empty, factorize by pivot_table throws error

df  = pd.DataFrame(columns=['sales','name','year'])
df1 = (df.pivot_table(index='name', columns='groups', values=['sale', 'year']))
df1.columns = [''.join(col) for col in df1.columns]
print (df1)

DataError:没有要聚合的数字类型

Answer 1

try:
    df1 = df.pivot_table(index='name', columns='name', values=['sale', 'year'])
except pd.core.groupby.DataError:
    df1 = pd.DataFrame()
except:
    raise

感谢 brenbarn，他在 How can I catch a pandas DataError? 找到了 dataerror 的错误名称