Question

I’m reading from two files (lists of datetimes), called A and B. (not necessarily in order)

I’d like to create a list of these datetimes as objects:

class AB(object):
    def __init__(self, datetime, a=False, b=False):
        self.datetime = datetime
        self.a = a
        self.b = b

a should be set to true if the datetime exists in file A, and b true if datetime exists in file B. (false otherwise)

For example:

file A: 20111225, 20111226
file B: 20111225, 20111227

List of objects should be:

AB(20111225, a = true, b = true)
AB(20111226, a = true, b = false)
AB(20111227, a = false, b = true)

Currently:

I’m reading through file A, putting the datetime into listA:

listObjects = []

fileA = open(A.log, 'rb')
listA = []
for line in fileA:
    try:
        dt = datetime.strptime(line, "%Y%m%d")
    except Exception, e:
        continue
    else:
        listA.append(dt)

Then reading through file B, checking if each item exists in listA, and adding to listObjects the B-only and A+B items:

fileB = open(B.log, 'rb')
for line in fileB:
    try:
        dt = datetime.strptime(line, "%Y%m%d")
    except Exception, e:
        continue
    else:
        if dt in listA:
            listA.remove(dt)
            listObjects.append(AB(dt, a=True, b=True))
        else: 
            listObjects.append(AB(dt, a=False, b=True))

I then loop through list A, adding the remaining A-only items:

for dt in listA:
    listObjects.append(AB(dt, a=True, b=False))

Then sort the list by datetime:

shutdowns.sort(key=lambda x: x.datetime)

---

Is there a better way to do this? This seems a bit clunky, and as the length of the files increases it’ll get exponentially slower.

I know you can get the intersection of lists by using set(A) & set(B) – should I use this?

Answer 1

Yes, using sets is a good idea. Take set(A) and set(B) then:

list_of_objects = [(i, i in A, i in B) for i in set(A) | set(B)]