issue_comments: 692945504

So the problem actually occurs when the MagicParameters class wraps an empty dictionary.

Relevant code:

https://github.com/simonw/datasette/blob/853c5fc37011a7bc09ca3a1af287102f00827c82/datasette/views/database.py#L228-L236

And:

https://github.com/simonw/datasette/blob/853c5fc37011a7bc09ca3a1af287102f00827c82/datasette/views/database.py#L364-L383

I'm passing a special magic parameters dictionary for the Python sqlite3 module to look up parameters in. When that dictionary is {} a __len__ check is performed on that dictionary, the result comes back as 0 and as a result it assumes there are no parameters.

I tracked down the relevant C code:

https://github.com/python/cpython/blob/81715808716198471fbca0a3db42ac408468dbc5/Modules/_sqlite/statement.c#L218-L237

```c Py_BEGIN_ALLOW_THREADS num_params_needed = sqlite3_bind_parameter_count(self->st); Py_END_ALLOW_THREADS

if (PyTuple_CheckExact(parameters) || PyList_CheckExact(parameters) || (!PyDict_Check(parameters) && PySequence_Check(parameters))) {
    /* parameters passed as sequence */
    if (PyTuple_CheckExact(parameters)) {
        num_params = PyTuple_GET_SIZE(parameters);
    } else if (PyList_CheckExact(parameters)) {
        num_params = PyList_GET_SIZE(parameters);
    } else {
        num_params = PySequence_Size(parameters);
    }
    if (num_params != num_params_needed) {
        PyErr_Format(pysqlite_ProgrammingError,
                     "Incorrect number of bindings supplied. The current "
                     "statement uses %d, and there are %zd supplied.",
                     num_params_needed, num_params);
        return;
    }

```

It looks to me like this should fail if the number of keys known to be in the dictionary differs from the number of named parameters in the query. But if those numbers fail to match it still works as far as I can tell - it's only dictionary length of 0 that is causing the problems.