Unpickling saved pytorch model throws AttributeError: Can't get attribute 'Net' on <module '__main__' despite adding class definition inline
I'm trying to serve a pytorch model in a flask app. This code was working when I ran this on a jupyter notebook earlier but now I'm running this within a virtual env and apparently it can't get attribute 'Net' even though the class definition is right there. All the other similar questions tell me to add the class definition of the saved model in the same script. But it still doesn't work. The torch version is 1.0.1 (where the saved model was trained as well as the virtualenv)
What am I doing wrong?
Here's my code.

import os
import numpy as np
from flask import Flask, request, jsonify 
import requests

import torch
from torch import nn
from torch.nn import functional as F


MODEL_URL = 'https://storage.googleapis.com/judy-pytorch-model/classifier.pt'


r = requests.get(MODEL_URL)
file = open("model.pth", "wb")
file.write(r.content)
file.close()

class Net(nn.Module):

    def __init__(self):
        super(Net, self).__init__()
        self.fc1 = nn.Linear(input_size, hidden_size)
        self.fc2 = nn.Linear(hidden_size, hidden_size)
        self.fc3 = nn.Linear(hidden_size, output_size)

    def forward(self, x):
        x = torch.sigmoid(self.fc1(x))
        x = torch.sigmoid(self.fc2(x))
        x = self.fc3(x)

        return F.log_softmax(x, dim=-1)

model = torch.load('model.pth')

app = Flask(__name__)

@app.route("/")
def hello():
    return "Binary classification example\n"

@app.route('/predict', methods=['GET'])
def predict():


    x_data = request.args['x_data']

    x_data =  x_data.split()
    x_data = list(map(float, x_data))

    sample = np.array(x_data) 

    sample_tensor = torch.from_numpy(sample).float()

    out = model(sample_tensor)

    _, predicted = torch.max(out.data, -1)

    if predicted.item() == 0: 
         pred_class = "Has no liver damage - ", predicted.item()
    elif predicted.item() == 1:
        pred_class = "Has liver damage - ", predicted.item()

    return jsonify(pred_class)


Here's the full traceback:

Traceback (most recent call last):
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/bin/flask", line 10, in &lt;module&gt;
    sys.exit(main())
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/flask/cli.py", line 894, in main
    cli.main(args=args, prog_name=name)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/flask/cli.py", line 557, in main
    return super(FlaskGroup, self).main(*args, **kwargs)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/click/decorators.py", line 64, in new_func
    return ctx.invoke(f, obj, *args, **kwargs)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/flask/cli.py", line 767, in run_command
    app = DispatchingApp(info.load_app, use_eager_loading=eager_loading)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/flask/cli.py", line 293, in __init__
    self._load_unlocked()
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/flask/cli.py", line 317, in _load_unlocked
    self._app = rv = self.loader()
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/flask/cli.py", line 372, in load_app
    app = locate_app(self, import_name, name)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/flask/cli.py", line 235, in locate_app
    __import__(module_name)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/app.py", line 34, in &lt;module&gt;
    model = torch.load('model.pth')
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/torch/serialization.py", line 368, in load
    return _load(f, map_location, pickle_module)
  File "/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/lib/python3.6/site-packages/torch/serialization.py", line 542, in _load
    result = unpickler.load()
AttributeError: Can't get attribute 'Net' on &lt;module '__main__' from '/Users/judyraj/Judy/pytorch-deployment/flask_app/liver_disease_finder/bin/flask'&gt;


This doesn't solve my issue. I do not want to change the way I persist the model. torch.save() worked fine for me outside the virtual env. I don't mind adding the class definition to the script. I'm trying to see what's causing the error despite that.

(This is a partial answer)
I don't think torch.save(model,'model.pt') works from the command prompt, or when a model is saved from one script running as '__main__' and loaded from another.
The reason is that torch must be automatically loading the module that was used to save the file, and it gets the module name from __name__.
Now for the partial part: It's unclear how to fix this issue, especially when you have virtualenvs in the mix.
Thanks to Jatentaki for starting the conversation in this direction.
