Need a program to exit after hitting a character python

Question

My script first reads a data file and then proceeds to analyze/plot it. I want the program to read the file line by line and then stop looking for lines upon hitting a # in the data file, at which point I'd like it to continue on the the rest it's code (plotting/analyzing, etc). I've been looking around and have tried sys.exit() and break but they don't allow for the program to continue on to it's analytic process, it just exits. Totally lost.

For more info....

for i in range(WL):
if(data[i][0]=='#'):comments=comments+1
else:
 #analytic stuff
 #more stuff

That was what was originally written in. This isn't my stuff, so I'm finding I get errors with this format, I'd like to revamp it and make the # a termination character. After trying @Lev_Levitsky's suggestion I now get an error of the type

flux=np.append(flux,data[i][1])
IndexError: list index out of range

Why would that happen?

Here's the new look

for i in range(WL):
 if '#' in line:
   break
 else:
  #analyze

Answer 1

break is what you need. It will take you out of the loop where you read lines from the file, and take you to whatever is after the loop:

with open('data') as f:
    for line in f:
       if '#' in line:
           break
       # do something else in the loop
       # like append something to a list

# analyze the data

Answer 2

Based on what you just showed us, what you want to do is this:

for i in range(WL):
    if(data[i][0]=='#'):
        comments=comments+1
        break
    else:
        #analytic stuff
        #more stuff

This is exactly the same as what Lev suggested, except I've spelled out explicitly where to put your break.