'NoneType' object is not iterable

Anvil Q&A
1

I’m trying to add the products that are medicines to the Medicines link.

I’ve tried using if and else, try and except, and isinstance(), but they didn’t really help.

def load_medicines(self, row):
medicines = anvil.server.call(‘get_all_medicines’, row)

for medicine in medicines:
  m = MedicineItem(name=medicine['name'], image=medicine['image'], price=f"{medicine['price']}", description=medicine['description'], button_callback=self.render_add_to_cart)
  self.content_panel.add_component(m)

https://anvil.works/build#clone:QYMBON3FCI6GPUUL=66EOLRYQSWUNC2U5BGH6GJZI

2

You are not returning anything from the server call:

ProductDetails:

@anvil.server.callable
def get_all_medicines(row):
  medicines_row = app_tables.categories.get(category="Medicines")
  row = app_tables.products.search(category=medicines_row)

This function does not return anything, so the caller will “receive” a None as a result of the anvil.server.call().
Hence the “NoneType” object.

  return app_tables.products.search(category=medicines_row)

Would be a way to fix this.

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3

It looks like you may be assuming that row is a single variable, passed by reference. In other languages, that’s a perfectly reasonable assumption. But here, it isn’t, for several good reasons.

First, get_all_medicines runs on a completely different computer from anvil.server.call. The computers aren’t sharing memory. So get_all_medicines can only receive a copy of row's value.

Second, in Python, the variable row that exists inside get_all_medicines is a completely separate variable, local to that particular call of get_all_medicines. As a result of the call, it initially points to the (received) copy of the value of caller’s row. Then, as a result of assignment, it no longer points to that copy, but points to the result of your app_tables.products.search call. After that, local variable row ceases to exist.

Either way, the in-browser variable row, whose value is passed in to the anvil.server.call, isn’t going to change. That’s an entirely separate variable.

2 Likes