Question

I have two files as shown below:

File 1 (tab delimited):

A1   someinfo1     someinfo2    someinfo3
A1   someinfo1     someinfo2    someinfo3
B1   someinfo1     someinfo2    someinfo3
B1   someinfo1     someinfo2    someinfo3

File 2 (tab delimited):

A1   newinfo1     newinfo2    newinfo3
A1   newinfo1     newinfo2    newinfo3
B1   newinfo1     newinfo2    newinfo3
B1   newinfo1     newinfo2    newinfo3

I want to read two lines together (lines starting with A1 and A1) from File 1 and two lines (lines starting with A1 and A1) from File 2. To be more clear, I have two requirements:

1) Reading two lines from the same file
2) Read same two lines from the other file.  

To be precise, I want to read four lines together ( 2 consecutive lines from two files (2 lines from each file)).

I searched online and was able to get a code to read two lines together but only from one file.

with open(File1) as file1:
        for line1,line2 in itertools.izip_longest(*[file1]*2):

Also, I was also able to read one line from each of the two files as:

for i,(line1,line2) in enumerate(itertools.izip(f1,f2)):
        print line1, line2

But I want to do sth like:

Pseudocode:

for line1, line2 from file1 and line_1 and line_2 from file2:
              compare line1 with line2
              compare line1 with line_1
              compare line2 with line_1
              compare line2 with line_2

I am hoping a solution to be a linear time one. All the files have same number of lines and the first column (primary id) is same for the consecutive lines within a file and the other file follows the same order (See the above example).

Thanks.

Answer 1

How about this:

with open('a') as A, open('b') as B:
    while True:
        try:
            lineA1, lineA2, lineB1, lineB2 = next(A), next(A), next(B), next(B)
            # compare lines
            # ...
        except StopIteration:
            break