python parse prints only first line from list

Question

I have a list \'a\',where I need to print all the matching letters of the list with the line of a text file \'hello.txt\'.But it only prints the first word from the list and

Answer 1

The file-object f is an iterator. Once you've iterated it, it's exhausted, thus your for line in f: loop will only work for the first key. Store the lines in a list, then it should work.

a=['comp','graphics','card','part']
with open('hello.txt', 'r') as f:
    lines = f.readlines()  # loop the file once and store contents in list
    for key in a:
        for line in lines:
            if key in line:
                print line, key

Alternatively, you could also swap the loops, so you iterate the file only once. This could be better if the file is really big, as you won't have to load all it's contents into memory at once. Of course, this way your output could be slights different (in a different order).

a=['comp','graphics','card','part']
with open('hello.txt', 'r') as f:
    for line in f:     # now the file is only done once...
        for key in a:  # ... and the key loop is done multiple times
            if key in line:
                print line, key

Or, as suggested by Lukas in the comments, use your original loop and 'reset' the file-iterator by calling f.seek(0) in each iteration of the outer key loop.