App with @dataclass decorator throws AttributeError

[davetapley]

I wanted to pass some config in, so I tried:

@dataclass
class MyApp(App):
    host: str
    port: int


MyApp(host, port).run()

But that causes:

    if self.devtools is not None:
AttributeError: 'MyApp' object has no attribute 'devtools'

...

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
line 2329, in _begin_update
    if self._sync_available:
AttributeError: 'MyApp object has no attribute '_sync_available'

There might not be a way to workaround it, but it would be nice if it could warn that @dataclass is not supported and suggest an alternative approach.

---

# Textual Diagnostics

## Versions

| Name    | Value  |
|---------|--------|
| Textual | 0.12.1 |
| Rich    | 13.3.1 |

## Python

| Name           | Value                                                    |
|----------------|----------------------------------------------------------|
| Version        | 3.10.9                                                   |
| Implementation | CPython                                                  |
| Compiler       | GCC 9.4.0                                                |
| Executable     | /home/dave/.pyenv/versions/3.10.9/envs/ng/bin/python3.10 |

## Operating System

| Name    | Value                                       |
|---------|---------------------------------------------|
| System  | Linux                                       |
| Release | 5.14.0-1034-oem                             |
| Version | #37-Ubuntu SMP Tue Apr 19 14:13:20 UTC 2022 |

## Terminal

| Name                 | Value           |
|----------------------|-----------------|
| Terminal Application | vscode (1.75.1) |
| TERM                 | xterm-256color  |
| COLORTERM            | truecolor       |
| FORCE_COLOR          | *Not set*       |
| NO_COLOR             | *Not set*       |

## Rich Console options

| Name           | Value               |
|----------------|---------------------|
| size           | width=84, height=59 |
| legacy_windows | False               |
| min_width      | 1                   |
| max_width      | 84                  |
| is_terminal    | True                |
| encoding       | utf-8               |
| max_height     | 59                  |
| justify        | None                |
| overflow       | None                |
| no_wrap        | False               |
| highlight      | None                |
| markup         | None                |
| height         | None                |

[davep]

You may find this entry in the FAQ helpful here.

[davetapley]

Ah excellent, yep that's what I ended up doing.

Will be interesting to see if this catches others out.