Check if a line in a file starts with a specific string - do some calculations

Question

So this is what im trying to do:

I have a huge file. I want to open it in python and look at each line, if it matches a certain predetermined string I want to get the number that comes immediately after that string, add them all up and get the average.

the file looks like this:

`$` Data
`$` Number of hours: 34
`$` DATA
`$` Number of hours: 56
`$` DATA3
`$` MoreDATA
`$` MOREDATA
`$` Number of hours: 9

I want to add 34 + 56 + 9 and then get the average.

So far this is what I have:

---

#fname = raw_input("Enter file name: ")
fh = open("data.txt")


fhread = fh.readlines()
#fhstrip = fhread.rstrip()
#fhstripz = fhstrip.lstrip()

findz = "Number of hours:"

for line in fhread:
    if line.startswith(findz)
    print line
    #print saved
    #spose = line.find('', atpos)


fh.close()    

print "Done"    

---

I dont know if I should use .read() or .readlines() ----When I use readlines it does not let me do rstrip and lstrip

Please help find all instances of the line with "Number of hours"

Answer 1

Treat the file as an iterator, which ensures that lines will only be read as they are actually needed, rather than caching the entire file in memory at once:

#fname = raw_input("Enter file name: ")
with open("data.txt") as fh:
    for line in fh:
        if line.startswith("Number of hours:"):
            print line