How do you Plot data generated by a python script?

I am fairly new to programing and have a question regarding matplotlib. I wrote a python script that reads in data from the outfile of another program then prints out the data from one column.

f = open( 'myfile.txt','r')
for line in f:
if line != ' ':
 line = line.strip()       # Strips end of line character
 columns = line.split() # Splits into coloumn
 mass = columns[8]    # Column which contains mass values
 print(mass)

What I now need to do is have matplotlib take the values printed in 'mass' and plot number versus mean mass. I have read the documents on the matplotlib website, but they don't really address how to get data from a script(or I just did not see it) If anyone can point me to some documentation that explains how I do this it would be really appreciated.
 Thanks in advance