for linesplit3 in 980981982983984985986 if data逾限原因1 is None data逾限原因1 = linesplit4修改代码

You can modify the code as follows:

for linesplit[3] in ["980","981","982","983","984","985","986"]:
    if data["逾限原因1"] is None:
        data["逾限原因1"] = linesplit[4]

This code checks if the value of data["逾限原因1"] is None. If it is None, then it assigns the value of linesplit[4] to data["逾限原因1"].