Objects disappear when I try to pass them to another class

Question

I'm trying to create a virtual model of a production plant. For that I created the following structure:

1. First of all there must be a parts file, which shows all the parts processed.
2. For each part there is a list of phases of the production cycle, which happen with different machines or instruments
3. Every machine of the same kind is grouped inside a workshop in the production plant, so there will also be a workshops file with informations about the shifts in which the workshop is operational
4. My first goal is to sort the parts file and create, for each part, new part objects that contain only phases that happen in the same workshop.
5. Then I want to assign each part object sorted with same workshop phases to the corresponding workshop object
6. Finally, I want to set the level of automation of every workshop object by looking at an information inside each parts phase called 'placings'

My problem is that the set_part method I created to fill each workshop with the corresponding parts doesn't seem to work.

I have placed some print statements here and there to check what was going on, and it seems that the objects are created correctly inside the loader class, but they don't get out of there.

This is the code:

class Phase:

def __init__(self, seq, workshop, placings):

    self.seq = seq
    self.workshop = workshop
    self.placings = placings

class Part:

def __init__(self, name, phases, workshop):

    self.name = name
    self.phases = phases
    self.workshop = workshop

class Workshop:

    def __init__(self, name, shifts, shift_dur):

        self.name = name
        self.shifts = shifts
        self.shift_dur = shift_dur

        self.parts = []
        self.automation = []

        print('parts inside workshop ', self.name, ':', self.parts)

        #this should assign the level of automation to the workshop
        automation = []
        for part in self.parts:
            for phase in part.phases:
                if phase.placings > 0:
                    automation.append('auto')
                else:
                    automation.append('manual')
        self.automation = automation

    def set_part(self, part):
        self.parts.append(part)

class Loader:

def __init__(self, cycles_file, workshops_file):

    self.cycles_file = cycles_file
    self.workshops_file = workshops_file
    self.workshops = []

    # those are some nested cycles that I use to create part objects with the same workshops
    parts = []
    for sheet in self.cycles_file:
        name = sheet
        phases = []
        workshops_set = set()
        for phase in self.cycles_file[sheet]:
            seq = phase['seq']
            workshop = phase['workshop']
            placings = phase['placings']
            workshops_set.add(workshop)
            phase = Phase(seq, workshop, placings)
            phases.append(phase)
        for workshop in workshops_set:
            same_workshops_phases = []
            for phase in phases:
                if workshop == phase.workshop:
                    same_workshops_phases.append(phase)
            part = Part(name, same_workshops_phases, workshop)
            parts.append(part)

    # creates workshop obj
    for workshop in self.workshops_file:
        name = workshop
        shifts = self.workshops_file[workshop]['Shifts']
        shift_dur = self.workshops_file[workshop]['Shift duration']
        workshop = Workshop(name, shifts, shift_dur)
        self.workshops.append(workshop)

    # setting parts for workshops
    for part in parts:
        for workshop in self.workshops:
            if workshop.name == part.workshop:
                workshop.set_part(part)


    for workshop in self.workshops:
        print('workshop: ', workshop.name)
        print('level of automation: ', workshop.automation)
        print('parts processed by workshop:')
        for part in workshop.parts:
            print(part.name)
            print('with phases:')
            for phase in part.phases:
                print(phase.seq)

There is an indentation error in the first line of class Loader, but it's just a copy/paste issue. Then I create the objects:

cycles_file =  {'p1': [{'seq': 10, 'workshop': 'ws1', 'placings': 2},
                   {'seq': 20, 'workshop': 'ws2', 'placings': 0}],
            'p2': [{'seq': 10, 'workshop': 'ws3', 'placings': 0}],
            'p3': [{'seq': 10, 'workshop': 'ws2', 'placings': 0},
                   {'seq': 20, 'workshop': 'ws1', 'placings': 3},
                   {'seq': 30, 'workshop': 'ws3', 'placings': 0}]}

workshops_file =    {'ws1': {'Shifts': 3, 'Shift duration': 8},
                 'ws2': {'Shifts': 2, 'Shift duration': 7.5},
                 'ws3': {'Shifts': 2, 'Shift duration': 7.5}}

loader = Loader(cycles_file, workshops_file)

this is the result I get:

parts inside workshop ws1 : []

parts inside workshop ws2 : []

parts inside workshop ws3 : []

workshop: ws1

level of automation: []

parts processed by workshop:

p1 with phases: 10

p3 with phases: 20

workshop: ws2

level of automation: []

parts processed by workshop:

p1 with phases: 20

p3 with phases: 10

workshop: ws3

level of automation: []

parts processed by workshop:

p2 with phases: 10

p3 with phases: 30

As you see, the parts inside workshops are empty and so the automation level can't be set...

Can somebody help me? I'm a self learner and I feel really lost!

Answer 1

Your code is fine, print is misleading you.

In class Workshop, pay attention here:

class Workshop:
    def __init__(self, name, shifts, shift_dur):
        self.parts = []
        self.automation = []

        print('parts inside workshop ', self.name, ':', self.parts)

You are printing parts inside workshops before set_part method runs.

As I mentioned before your code is fine, the parts inside workshops are NOT empty, just test it with:

for workshop in loader.workshops:
    print('parts inside workshop ', workshop.name, ':', workshop.parts)