Iterating over a file twice
Basically what you do is:
for line in somefile: pass # first run
for line in somefile: pass # second run
The first run will complete just fine, the second run will not run at all.
This is because the file was read until the end and there's no more data to read lines from.
Call somefile.seek(0)
to go to the beginning of the file:
for line in somefile: pass # first run
somefile.seek(0)
for line in somefile: pass # second run
Storing things uniquely
Basically, what you seem to want is a way to store the IDs from the file in the a data structure and every id shall only be once in said structure.
If you want to store elements uniquely you use, for example, dictionaries (help(dict)
)
or sets (help(set)
). Example with sets:
myset = set()
myset.add(2) # set([2])
myset.add(3) # set([2,3])
myset.add(2) # set([2,3])