pdconcatdf1 df-2-1可以运行但是pdconcatdf1 df-2-1运行失败

The reason why pd.concat([df[:1], df[-2:-1]]) runs successfully but pd.concat(df[:1], df[-2:-1]) fails is because the pd.concat() function expects the first argument to be a list of DataFrames or Series to concatenate.

In the first example, pd.concat([df[:1], df[-2:-1]]), the square brackets [] are used to create a list containing the two DataFrame slices df[:1] and df[-2:-1]. This list is then passed as the first argument to pd.concat(), and the function is able to concatenate the DataFrames successfully.

In the second example, pd.concat(df[:1], df[-2:-1]), the square brackets are not used, so the function is called with two separate arguments df[:1] and df[-2:-1]. Since pd.concat() expects a list as the first argument, it raises an error because it is not able to concatenate the two separate DataFrames.

To fix the issue, you need to wrap the DataFrame slices in a list when calling pd.concat(), like this: pd.concat([df[:1], df[-2:-1]]).