Wsrtjtyk

I am new to python.
I have a data frame with a column called "temp_signal" already with 1,-1,or 0, and am trying to modified the number via the code below.
The logic is to reassign numbers based on what I already have.
if 1 or -1,keep the value;
if the value becomes 0, loop back to previous one till non 0 value;

like this
enter image description here

I am also setting up a new column "final signal" to collect the output. But different errors are reported. Can anyone help? Thanks

import pandas as pd

import numpy as np

import xlrd as xl



TRND= pd.read_excel("C:\Users\Downloads\file.xlsx")

def final():

    for i in range(len(TRND["temp_signal"])):

        df=TRND["temp_signal"]

        data=pd.DataFrame()

        if df[i]==0:

            j=1

            while df[i]==0:

                df=df[i-j]

                j=j+1

            data=data.append(df)

            return data

        else:

            data=data.append(df)

            return data

TRND["final_signal"]=final()

print(TRND["final_signal"].describe())