[Sqlalchemy-tickets] Issue #4018: maintaining float type affinity (zzzeek/sqlalchemy)

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

New issue 4018: maintaining float type affinity
https://bitbucket.org/zzzeek/sqlalchemy/issues/4018/maintaining-float-type-affinity

Michael Bayer:

continuing from #4017

two issues are 1. the "asdecimal"-ness of an expression being maintained, which goes beyond Float and 2. Float having it's own affinity



```
#!python

from sqlalchemy import Float, Integer, literal
expr = literal(5, Integer) * literal(4.5, Float)
assert expr.type.asdecimal is False
assert expr.type is Float

```

option are to give Float its own _type_affinity, but then that only works for Float and not Numeric with asdecimal=False type affinity and also that would be the single example of two levels of _type_affinity Numeric/Float so not sure I like that.

I think we should use something other than _type_affinity in _DateAffinity._adapt_expression that can deliver more specificity, and leave _type_affinity alone since this is not as much about Python datatypes.

also why are the logic used for numeric -> numeric type adaptations encapsulated in _DateAffinity, that just looks bad, rename that to something.