int('2.1') does not work while int(float('2.1')) does

[Joe Mason]

In article <40722555.66C70D40 at alcyone.com>, Erik Max Francis wrote:
> There's a fundamental difference between an int and a float.  If the
> string you're trying to convert looks like a float, that means it
> doesn't look like an int.
> 
> With your first example of '2.1', what should it mean?  Should it
> truncate, round to negative infinity round to positive infinity, round
> to zero, what?  Python can't guess for you, so it shouldn't try.  Thus
> it's an error.

Why can it make this guess for "int(2.1)", then?  It's got a rule for
converting floats to ints - why not use it here?

Joe