Hi Alfonso,
I see you've had some responses yet -- I've not read them all, and am just
posting the following suggestion you might want to look at:
# read lines with "keys" into a list
selected_keys=open('A.txt', 'r').readlines()
# read all data records into another list
records=open('B.txt', 'r').readlines()
# Now use a list comprehension to return the required entries, the i+1th
entries for all i indexes in the records
# list that corresponds to a key in the keys list:
selected_values = [(records[i], records[i+1]) for i, row in
enumerate(records) if row in selected_keys]
# The above returns both the key and the value, in a tuple, if you just
want the value rows only then the above becomes:
#selected_values = [records[i+1] for i, row in enumerate(records) if row in
selected_keys]
# Finally print the result.
print selected_values
You'll note I read both files into memory, even though you say your files
are largish. I don't consider 500MB to be very large in this day and age
of 4+GB PC's, which is why I've basically ignored the "large" issue. If
this is not true in your case then you'll have to post back.
Good luck,
Walter
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