Replacing text in a file

Question

I'm new to python,I wanted to replace text or more specifically words in a file using the list in excel. So,was doing my research and wrote the code. But I'm stuck at a place.

First was trying to replace in same file :-

for line in file:
    i=0
    for x in range(nrows):  
        file.write(line.replace(sheet1.cell(i,0).value,sheet1.cell(i,1).value))
        #print(string)
        i=i+1

file.close()  

It was replacing but also replicating the line multiple times.

So I researched and found other way that was writing in Two different files and with a string variable.

Here is the code for it :-

for line in file:
    i=0
    string=line
    for x in range(nrows):  
        string.replace(sheet1.cell(i,0).value,sheet1.cell(i,1).value)
        #print(string)
        i=i+1
    file1.write(string)
    #print(string)

But Now It's not replacing anything just copy pasting the code.

Can anyone pls guide me with both ways ....

So as per the post https://stackoverflow.com/questions/5453267/is-it-possible-to-modify-lines-in-a-file-in-place

I have Inculcated the fileinput function

But after running the script the file becomes blank

Can you pls tell me...

My Updated Code :-

for line in fileinput.input(filepath,inplace=True, backup='.bak'):
    i=0
    for x in range(nrows):  
        line.replace(sheet1.cell(i,0).value,sheet1.cell(i,1).value)
        #print(string)
        i=i+1