Question

I’ve been using python for a couple years on and off, but not much for complicated object oriented programming and I rarely use dictionaries as a structure. For this application I’m trying to build a database of geo-located waypoints on a map.

As such, I want to create a container class that is capable of accessing a 2-D dictionary structure and performing various methods. In the interest of usability and readability, I’m trying to implement the various container methods, but I’m having a hard time adding the class functionality.

A snippet of my container class

# Python standard libraries
from collections import defaultdict
from GeoWayPt import *
#===========================================================================
class GeoWayPtData():
    """ Geodetic waypoint data container """

    # Nested dictionary structure for equipment/waypoints
    def equip_dict(self): return defaultdict(self.waypt_dict)
    def waypt_dict(self): return GeoWayPt

    def __init__(self):
        """ Constructor """
        #
        self.AvailEquipIndex = 0

        # Nested dictionary of equipment with waypoints
        #
        # First key for each equipment.
        # Second key for each waypoint.
        # [EquipNum][WayptNum]
        self.dictWayPts = defaultdict(self.equip_dict)

I wasn’t sure how to implement the iter and next methods in order to achieve the looping functionality in the test script below.

Part of my data class

class GeoWayPt():
    """ Geodetic waypoint container class """
    def __init__(self):
        """ Constructor """
        # Equipment ID (integer, starting at 0)
        self.ID = 0
        # Equipment class (string description)
        self.EquipClassStr = ''

My test script

from GeoWayPt import *
from GeoWayPtData import *

# 2-D data structure
data = GeoWayPtData()

waypt = GeoWayPt()
waypt.ID = 0
waypt.EquipClassStr = "foo"
# Add equipment 0
data.AddEquip(waypt)

waypt = GeoWayPt()
waypt.ID = 0
waypt.EquipClassStr = "bar"
# Add waypoint to equipment 0
data.AddWayPt(0, waypt)

waypt = GeoWayPt()
waypt.ID = 1
waypt.EquipClassStr = "can"
# Add equipment 1
data.AddEquip(waypt)

waypt = GeoWayPt()
waypt.ID = 1
waypt.EquipClassStr = "haz"
# Add waypoint to equipment 1
data.AddWayPt(1, waypt)

waypt = GeoWayPt()
waypt.ID = 1
waypt.EquipClassStr = "sum"
# Add another waypoint to equipment 1
data.AddWayPt(1, waypt)

# Functionality I'd like:
for equip in data:
    for waypt in equip:
        print waypt.ID, waypt.EquipClassStr

Answer 1

Instead of trying to support iteration in GeoWayPtData, it may be easier to iterate over the defaultdict in GeoWayPtData:

for equip in data.dictWayPts.itervalues():
    for waypt in equip.itervalues():
        print waypt.ID, waypt.EquipClassStr

Of course you could also add this functionality to GeoWayPtData by adding an __iter__ that yields the waypoints:

    def __iter__(self):
        for equip in self.dictWayPts.itervalues():
            for waypt in equip.itervalues():
                yield waypt

Then you could do this:

for waypt in data:
    print waypt.ID, waypt.EquipClassStr