issue_comments

Rest of the work on this will happen in the PR: - #2080

This is bad: python async def __call__(self, request, datasette): try: handler = getattr(self, request.method.lower()) return await handler(request, datasette) except AttributeError: return await self.method_not_allowed(request) Because it hides any AttributeError exceptions that might occur in the view code.

I'm going to call this VerbView for the moment. Might even rename it to View later.

Here's a new BaseView class that automatically populates OPTIONS based on available methods: ```python class BaseView: async def head(self, args, kwargs): try: response = await self.get(args, **kwargs) response.body = b"" return response except AttributeError: raise

async def method_not_allowed(self, request):
    if (
        request.path.endswith(".json")
        or request.headers.get("content-type") == "application/json"
    ):
        response = Response.json(
            {"ok": False, "error": "Method not allowed"}, status=405
        )
    else:
        response = Response.text("Method not allowed", status=405)
    return response

async def options(self, request, *args, **kwargs):
    response = Response.text("ok")
    response.headers["allow"] = ", ".join(
        method.upper()
        for method in ("head", "get", "post", "put", "patch", "delete")
        if hasattr(self, method)
    )
    return response

async def __call__(self, request, datasette):
    try:
        handler = getattr(self, request.method.lower())
        return await handler(request, datasette)
    except AttributeError:
        return await self.method_not_allowed(request)

class DemoView(BaseView): async def get(self, datasette, request): return Response.text("Hello there! {} - {}".format(datasette, request))

post = get

```

Actually no need for that extra level of parameter detection: BaseView.__call__ should always take datasette, request - scope and receive are both available on request, and send is only needed if you're not planning on returning a Response object.

So the get and post and suchlike methods should take datasette and request too.

This prototype seems to work well:

```diff diff --git a/datasette/app.py b/datasette/app.py index d7dace67..ed0edf28 100644 --- a/datasette/app.py +++ b/datasette/app.py @@ -17,6 +17,7 @@ import secrets import sys import threading import time +import types import urllib.parse from concurrent import futures from pathlib import Path @@ -1266,6 +1267,8 @@ class Datasette: # TODO: /favicon.ico and /-/static/ deserve far-future cache expires add_route(favicon, "/favicon.ico")

• add_route(wrap_view(DemoView, self), '/demo') + add_route( asgi_static(app_root / "datasette" / "static"), r"/-/static/(?P<path>.*)$" ) @@ -1673,8 +1676,46 @@ def _cleaner_task_str(task): return _cleaner_task_str_re.sub("", s)

-def wrap_view(view_fn, datasette): - @functools.wraps(view_fn) +class DemoView: + async def call(self, datasette, request): + return Response.text("Hello there! {} - {}".format(datasette, request)) + +def wrap_view(view_fn_or_class, datasette): + is_function = isinstance(view_fn_or_class, types.FunctionType) + if is_function: + return wrap_view_function(view_fn_or_class, datasette) + else: + if not isinstance(view_fn_or_class, type): + raise ValueError("view_fn_or_class must be a function or a class") + return wrap_view_class(view_fn_or_class, datasette) + + +def wrap_view_class(view_class, datasette): + async def async_view_for_class(request, send): + instance = view_class() + if inspect.iscoroutinefunction(instance.call): + return await async_call_with_supported_arguments( + instance.call, + scope=request.scope, + receive=request.receive, + send=send, + request=request, + datasette=datasette, + ) + else: + return call_with_supported_arguments( + instance.call, + scope=request.scope, + receive=request.receive, + send=send, + request=request, + datasette=datasette, + ) + + return async_view_for_class + + +def wrap_view_function(view_fn, datasette): async def async_view_fn(request, send): if inspect.iscoroutinefunction(view_fn): response = await async_call_with_supported_arguments( ```

Maybe what I want here is the ability to register classes with the router - and have the router know that if it's a class it should instantiate it via its constructor and then await __call__ it.

The neat thing about it is that it can reduce the risk of having a class instance that accidentally shares state between requests.

It also encourages that each class only responds based on the datasette, request, ... objects that are passed to its methods.

Oops, that broke everything: ``` @documented async def await_me_maybe(value: typing.Any) -> typing.Any: "If value is callable, call it. If awaitable, await it. Otherwise return it."

  if callable(value):

E TypeError: 'module' object is not callable ```

With type hints and a namedtuple: ```python import asyncio import types from typing import NamedTuple, Any

class CallableStatus(NamedTuple): is_callable: bool is_async_callable: bool

def check_callable(obj: Any) -> CallableStatus: if not callable(obj): return CallableStatus(False, False)

if isinstance(obj, type):
    # It's a class
    return CallableStatus(True, False)

if isinstance(obj, types.FunctionType):
    return CallableStatus(True, asyncio.iscoroutinefunction(obj))

if hasattr(obj, "__call__"):
    return CallableStatus(True, asyncio.iscoroutinefunction(obj.__call__))

assert False, "obj {} is somehow callable with no __call__ method".format(repr(obj))

python for thing in ( async_func, non_async_func, AsyncClass(), NotAsyncClass(), ClassNoCall(), AsyncClass, NotAsyncClass, ClassNoCall, ): print(thing, check_callable(thing)) <function async_func at 0x1073d5120> CallableStatus(is_callable=True, is_async_callable=True) <function non_async_func at 0x1073d5080> CallableStatus(is_callable=True, is_async_callable=False) <main.AsyncClass object at 0x106ba7490> CallableStatus(is_callable=True, is_async_callable=True) <main.NotAsyncClass object at 0x106740150> CallableStatus(is_callable=True, is_async_callable=False) <main.ClassNoCall object at 0x10676d910> CallableStatus(is_callable=False, is_async_callable=False) <class '__main__.AsyncClass'> CallableStatus(is_callable=True, is_async_callable=False) <class '__main__.NotAsyncClass'> CallableStatus(is_callable=True, is_async_callable=False) <class '__main__.ClassNoCall'> CallableStatus(is_callable=True, is_async_callable=False) ```

I don't like that is_callable() implies a single boolean result but actually returns a pair. I'll call it check_callable(obj) instead.

I think I want that to return (is_callable, is_async) - so I can both test if the thing can be called AND if it should be awaited in the same operation (without any exceptions).

I tried this: ```python def is_callable(obj): "Returns (is_callable, is_async_callable)" if not callable(obj): return False, False

if isinstance(obj, types.FunctionType):
    return True, asyncio.iscoroutinefunction(obj)

if hasattr(obj, '__call__'):
    return True, asyncio.iscoroutinefunction(obj.__call__)

return False, False

python for thing in ( async_func, non_async_func, AsyncClass(), NotAsyncClass(), ClassNoCall(), AsyncClass, NotAsyncClass, ClassNoCall ): print(thing, is_callable(thing)) And got: <function async_func at 0x1073d5120> (True, True) <function non_async_func at 0x1073d5080> (True, False) <main.AsyncClass object at 0x106cce490> (True, True) <main.NotAsyncClass object at 0x106ccf710> (True, False) <main.ClassNoCall object at 0x106ccc810> (False, False) <class '__main__.AsyncClass'> (True, True) <class '__main__.NotAsyncClass'> (True, False) <class '__main__.ClassNoCall'> (True, False) `` Which is almost right, but I don't like thatAsyncClassis shown as callable (which it is, since it's a class) and awaitable (which it is not - thecall` method may be async but calling the class constructor is not).

So I'm going to detect classes using isinstance(obj, type).

```python def is_callable(obj): "Returns (is_callable, is_async_callable)" if not callable(obj): return False, False

if isinstance(obj, type):
    # It's a class
    return True, False

if isinstance(obj, types.FunctionType):
    return True, asyncio.iscoroutinefunction(obj)

if hasattr(obj, '__call__'):
    return True, asyncio.iscoroutinefunction(obj.__call__)

assert False, "obj {} somehow is callable with no __call__ method".format(obj)

`` I am reasonably confident theAssertionError` can never be raised.

And now: <function async_func at 0x1073d5120> (True, True) <function non_async_func at 0x1073d5080> (True, False) <__main__.AsyncClass object at 0x106ccfa50> (True, True) <__main__.NotAsyncClass object at 0x106ccc8d0> (True, False) <__main__.ClassNoCall object at 0x106cd7690> (False, False) <class '__main__.AsyncClass'> (True, False) <class '__main__.NotAsyncClass'> (True, False) <class '__main__.ClassNoCall'> (True, False) Which is what I wanted.

After much fiddling this seems to work: ```python import asyncio, types

def is_async_callable(obj): if not callable(obj): raise ValueError("Object is not callable")

if isinstance(obj, types.FunctionType):
    return asyncio.iscoroutinefunction(obj)

if hasattr(obj, '__call__'):
    return asyncio.iscoroutinefunction(obj.__call__)

raise ValueError("Not a function and has no __call__ attribute")

Tested like so:python class AsyncClass: async def call(self): pass

class NotAsyncClass: def call(self): pass

class ClassNoCall: pass

async def async_func(): pass

def non_async_func(): pass

for thing in (AsyncClass(), NotAsyncClass(), ClassNoCall(), async_func, non_async_func): try: print(thing, is_async_callable(thing)) except Exception as ex: print(thing, ex) <main.AsyncClass object at 0x106c32150> True <main.NotAsyncClass object at 0x106c32390> False <main.ClassNoCall object at 0x106c32750> Object is not callable <function async_func at 0x1073d5120> True <function non_async_func at 0x1073d5080> False ```

I may need to be able to detect if a class instance has an async def __call__ method - I think I can do that like so:

python def iscoroutinefunction(obj): if inspect.iscoroutinefunction(obj): return True if hasattr(obj, '__call__') and inspect.iscoroutinefunction(obj.__call__): return True return False From https://github.com/encode/starlette/issues/886#issuecomment-606585152

So I think subclasses of BaseView need to offer a callable which accepts all five of the DI arguments - datasette, request, scope, send, receive - and then makes a decision based on the HTTP verb as to which method of the class to call. Those methods themselves can accept a subset of those parameters and will only be sent on to them.

Having two layers of parameter detection feels a little bit untidy, but I think it will work.

The idea behind wrap_view() is dependency injection - it's mainly used by plugins:

https://docs.datasette.io/en/0.64.3/plugin_hooks.html#register-routes-datasette

But I like the pattern so I started using it for some of Datasette's own features.

I should use it for all of Datasette's own features.

But I still like the way BaseView helps with running different code for GET/POST/etc verbs.

Here's what wrap_view() does:

https://github.com/simonw/datasette/blob/49184c569cd70efbda4f3f062afef3a34401d8d5/datasette/app.py#L1676-L1700

It's used e.g. here:

https://github.com/simonw/datasette/blob/49184c569cd70efbda4f3f062afef3a34401d8d5/datasette/app.py#L1371-L1375

The BaseView thing meanwhile works like this:

https://github.com/simonw/datasette/blob/d97e82df3c8a3f2e97038d7080167be9bb74a68d/datasette/views/base.py#L56-L157