How to avoid "f.close" (no parens) bug?

[Terry Reedy]

"Paul Prescod" <paul at prescod.net> wrote in message
news:402BB684.4010807 at prescod.net...
> Michael Pyle wrote:
> > try:
> >         sys.frozen
> > except AttributeError:
> >         options.append( 'debug-on' )
>
> A cleaner and probably more efficient way of doing this is:

Since I expect, based on old posts but without testing the current
interpreter, the fixed cost of hasattr to be between the two costs of
successful and exception-generating tries (the latter much higher), I would
expect relative efficiency to depend on the relative proportion of try
outcomes.  But the difference should seldom be enough to be a deal breaker
either way.

Regardless of speed, I like the below better.  The bare attribute access is
a bit jarring to me, though I can see how it might become an in-house
idiom.

> if not hasattr(sys, "frozen"):
> options.append("debug-on")

But for similar reasons, even if there were no use for bare names, I would
be opposed to breaking the currently simplicity of 'name recalls object'.
In any case, a Python compiler cannot, in general, know what type of object
a name will be bound to at runtime.  The parens following a name (or
expression) amount to a behavioral-type promise by the programmer that the
resulting object will be callable.  If not, then a *runtime* exception gets
raised.  In return, the interpreter promises to make the call if at all
possible.

Terry J. Reedy