Question

There is an error earlier in the program that I am attempting to find, but was asked to explain what is happening in this part of the code. Below is the code and what I think it is doing, but am unclear on some certain points. Some help in understanding would be greatly appreciated.

for title in titles:
    secString = 'sec_%02d' % (title)
    titleCitations = [c for c in cEdges if secString in c[0]]
    intraCitations = [c for c in titleCitations if secString in c[1]]
    print title, len(titleCitations), len(intraCitations), len(titleCitations) - len(intraCitations)

First, secString takes the remainder of 'sec_%02d' with respect to title, (I think this is just finding all strings that have a reference to a title?). It then creates a list titlecitations.

Though I am confused by the bracketed part. If I understand correctly, it takes the cEdge which I believe is just a list of a pairing of numbers from a given US legal code reference i.e. 26 USC 501 becomes just (26, 501), and asks if secString has a value in the c[0] spot.

(This is where I get confused; I am guessing that the c[0] spot maybe corresponds to the 26 in the above example and c[1] would correspond to the 501? Of course I am not even sure if I am understanding the c part correctly.)

Then put it in titlecitations if the c[0] spot is filled. It then creates the intracitations list. This list looks at the titlecitations list and asks if in secString is the c[1] filled and if so put it in this list.

I know there is a problem with something because titlecitations and intracitations appear to be the same list then.

Answer 1

secString = 'sec_%02d' % (title)

The % operator on a string isn’t modulus, it’s a formatting operator that behaves like C’s printf(). %02d is a formatting code that formats title as a two-digit number. If title is only one digit then it pads it with a 0 (e.g. 9 becomes 09).

(This is where I get confused; I am guessing that the c[0] spot maybe corresponds to the 26 in the above example and c[1] would correspond to the 501? Of course I am not even sure if I am understanding the c part correctly.)

That is correct.

titleCitations = [c for c in cEdges if secString in c[0]]

This searches through the items in cEdges and finds ones where the title contains the string sec_XY where XY is that two-digit number from earlier.

intraCitations = [c for c in titleCitations if secString in c[1]]

Now it searches through the things we found in the previous step, again searching for the sub-string sec_XY.

The end result is that intraCitations contains a list of all the items from cEdges where both the first and second item contain the substring sec_XY.