[Sqlalchemy-tickets] Issue #4262: 3rd party dialect Type not resolved for compile (zzzeek/sqlalchemy)

[Patrick B. <iss...@bi...>]

New issue 4262: 3rd party dialect Type not resolved for compile
https://bitbucket.org/zzzeek/sqlalchemy/issues/4262/3rd-party-dialect-type-not-resolved-for

Patrick Buxton:

A type declared in a 3rd party dialect does not get resolved when you ask it to compile and results in a:
UnsupportedCompilationError: Compiler <sqlalchemy.sql.compiler.GenericTypeCompiler object at 0x0000000005C48CC0> can't render element of type <class 'sqlalchemy_hana.types.TINYINT'>

```
#!python

from sqlalchemy import Table, MetaData, Column
from sqlalchemy_hana.types import TINYINT
meta = MetaData()
t = Table('test_table', meta, Column('Col1', TINYINT))
str(t.columns['Col1'].type)
```
The problem stems from type_api _default_dialect where it's happy to lookup within the included dialects. Given that the 3rd party dialects are supposed to follow specific naming conventions, would it be possible to provide a lookup on that basis too?


```
#!python

    def _default_dialect(self, default):
        if self.__class__.__module__.startswith("sqlalchemy.dialects"):
            tokens = self.__class__.__module__.split(".")[0:3]
            mod = ".".join(tokens)
            return getattr(__import__(mod).dialects, tokens[-1]).dialect()
        else:
            return default.DefaultDialect()
```