dflocdf编号 == mailNumber 到达时间 = tdopTimeStart1809 in _setitem_with_indexer raise ValueErrorValueError cannot set a frame with no defined index and a scalar

The error message indicates that you are trying to assign a scalar value to a DataFrame using loc, but the DataFrame has no defined index.

To resolve this issue, you need to set the DataFrame index before assigning values using loc. You can do this by using the set_index method on your DataFrame, specifying the column that you want to set as the index.

Here's an example of how you can set the index and assign a value using loc:

df = df.set_index("编号")  # Set "编号" column as the index
df.loc[mailNumber, "到达时间"] = tdopTimeStart  # Assign value to "到达时间" column for the specified mailNumber

Make sure to replace "编号" with the actual column name in your DataFrame, and mailNumber and tdopTimeStart with the appropriate values in your code.