Question

I’m passing a set of MovieFile objects from x.py to y.py and iterating through them, trying to use each object’s attributes in y.py

x.py

mfSet = {}

def pop():
    ## populate mfSet with MovieFile objects
    m = MovieFile(title=t, year=y, dir=d, filename=f)
    mfSet.setdefault(str(m), []).append(m)

class MovieFile():
    def __init__(self, title, dir, filename, year=0):
        self.title = title
        self.year = year
        self.fulltitle = title if year == 0 else title + ' (' + year + ')'
        self.dir = dir
        self.filename = filename
    def __str__(self):
        return repr(self.title + ' (' + self.year + ') at ' + self.dir)

y.py

from x import MovieFile, mfSet, pop # not sure if I need to import MovieFile

pop()

for mf in mfSet:
    ft = mf.fulltitle # stacktrace says this attr doesn't exist for str object
    title = mf.title # printing shows that this is "<built-in method title of str object at 0x10d84a3f0>"

So my main questions are:

Why are the MovieFile objects compiling as str objects, and how can I use the fulltitle attr once I get use of those objects?

Answer 1

You haven’t shown what pop is (please include that code, it’s the important bit). However, I expect what the problem is that mfSet is a dict and you are assigning str keys—perhaps mfSet[str(mf)] = mf. Iteration of a dict produces the keys, not the values of a dictionary.

You may want to use a set instead of a dict. Or, change for mf in mfSet: to for mf in mfSet.itervalues(): (and change the variable name mfSet to not be misleading about type; PEP 8 also recommends against camelCase in variable names).

---

So, you’re grouping by MovieFile.__str__(). Very well, then. Here’s how I might write that code:

from collections import defaultdict

mf_collection = defaultdict(list)

def pop():
    ## populate the collection with MovieFile objects
    m = MovieFile(title=t, year=y, dir=d, filename=f)
    mf_collection[str(m)].append(m)

class MovieFile():

    def __init__(self, title, dir, filename, year=0):
        self.title = title
        self.year = year
        self.fulltitle = title if year == 0 else title + ' (' + year + ')'
        self.dir = dir
        self.filename = filename

    def __str__(self):
        return repr(self.title + ' (' + self.year + ') at ' + self.dir)

And y.py:

from x import mf_collection, pop

pop()

for mf_group in mf_collection.itervalues():  # this yields lists of MovieFiles
    for mf in mf_group:  # this yields the actual MovieFiles
        ft = mf.fulltitle
        title = mf.title

Because you’re working with lists being the values, you’ve got another level of iteration to do.