(使用pandas)数据库单元格在函数之外不会更新。怎么办?

因此,我试图使用上面和下面一行中的值的平均值来填充缺失的数据行。我对编码相对较新,所以我对任何不简洁的代码表示歉意。

以下是我使用的函数和一些数据。

import pandas

def avg_round(a,b,c):
    x = float(round((a + b)/2,c))
    return x

def fill_in_single(c,ro): ##ro signifies to how many digits I need to round the new value to, "c" is the column we need to edit
    m_list = single_missing(c) ##this list has all the rows that are empty in the column "c"
    for i_obj in m_list:
        act_row=i_obj-2 ##I need to do this because the rows are stored as their excel row numbers which is different from the pandas df row number
        prev_row=act_row-1
        next_row=act_row+1
        prev_val=c[prev_row]
        next_val=c[next_row]
        new_val=avg_round(prev_val,next_val,ro)
        df.at[act_row,'{}'.format(c)] = new_val

fill_in_single(Column,0)
print(df.at[2,'Column'])

OUTPUT:
nan

   Index Column
    0       1
    1       9
    2 
    3       0

因此,当我运行此命令并尝试打印一个所谓的“更新”列的值时,我得到的是“nan”而不是new_val。我在函数中运行了此打印命令,它返回了new-val。我真的不确定该怎么办?

我还运行了函数外的代码,它正确地更新了列。那么,为什么这个功能不起作用呢?