Python. Showing text from a file in fragments of 20 lines every time ENTER is pressed.

Question

This is the code i have at the moment

print "Please input the filename:"
n = raw_input()
f = open(n,"r")
x = 0
for line in f.readlines():
    print line
    x+=1
    if x % 20 == 0:
        break
        q = raw_input()
        if q == "":
            x+= 20
        continue

Things the program should do: 1) Ask for a filename 2) Read the file 3) Print the first 20 lines of the file 4) Stop working after the first 20 lines and wait for an Enter keypress 5) If Enter is pressed show the next 20 lines of the file (20->40 and so on)

Current problem: The loop doesn't restart, it only shows the first 20 lines and then stops working.

Answer 1

Basically, you want to pause every 20 lines. Currently, you're breaking out of your loop after the first 20 lines.

for line in f:
    print line
    x += 1
    if x % 20 == 0:
        raw_input("Hit enter")

should suffice.

Answer 2

filename = raw_input("Please enter the file name: ")
with open(filename) as f:
    lines = f.readlines()
    for i in xrange(0, len(lines), 20):
        print lines[i:i+20]
        raw_input("Press Enter for more")

This reads the whole file into memory so you might not want to use slices if it's a huge file. But if it's a huge file, you're unlikely to want to step through it twenty lines at a time ;)

The major change is that we are opening the file using a with statement. This is much nicer than using open/close and guarantees that the file will always be closed.

in the code that you posted, when you executed break, you were exiting your look. break leaves the loop so you only want to use it for that purpose. just calling a blocking operation likeraw_input` suffices if you just need to pause execution for some reason (like waiting on the user).

also, the continue is entirely unnecessary. At the end of the body of a loop, it has no choice but to continue

What were you thinking with the linesif q == "": x += 20? first off, it should just be if not q: x += 20 (empty string (like empty lists/dicts/tuples) evaluates to False) and second, this would skip the next 20 lines. Is this a requirement that you haven't shared?