您可以使用:

df['TradeDate'] = pd.to_datetime(df['TradeDate'], format='%Y%m%d.0')
print (df)
   TradeDate
0 2010-03-29
1 2010-03-28
2 2010-03-29

但是如果一些错误的值，添加 errors='coerce' 以替换它们到 NaT

But if some bad values, add errors='coerce' for replace them to NaT

print (df)
    TradeDate
0  20100329.0
1  20100328.0
2  20100329.0
3  20153030.0
4         yyy

df['TradeDate'] = pd.to_datetime(df['TradeDate'], format='%Y%m%d.0', errors='coerce')
print (df)
   TradeDate
0 2010-03-29
1 2010-03-28
2 2010-03-29
3        NaT
4        NaT