Count the number of iterations of a if loop

I have the following if loop:

for line in content[:-1]:
 # if the line has No Data in it
    if line.find("No Data"):
        line = line.replace("No Data", "0")

What the if loop does is to read every line of a list called "Content" and whe it detects the words "No Data" it subtitutes them for a Zero value. What I would like to do is to Count how many times this Change is done; I've tried with the following:

ctr=0
for line in content[:-1]:
    if line.find("No Data"):
        line = line.replace("No Data", "0")
        ctr +=1

But what I got is that crt equals the total value of lines instead the number of times that that Change is done.