[Python-bugs-list] [ python-Bugs-481726 ] literal fp pound errors pass silently

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Bugs item #481726, was opened at 2001-11-14 08:00
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Category: None
Group: Not a Bug
Status: Closed
Resolution: Invalid
Priority: 5
Submitted By: Grant Griffin (dspguru)
Assigned to: Nobody/Anonymous (nobody)
Summary: literal fp pound errors pass silently

Initial Comment:
It looks like anything beyond a pound sign in a 
floating point literal is allowed, but ignored.  Here 
are a couple of examples:

----------

Python 2.2b1 (#25, Oct 19 2001, 11:44:52) [MSC 32 bit 
(Intel)] on win32
Type "help", "copyright", "credits" or "license" for 
more information.
>>> a=1.#INF
>>> a
1.0

ActivePython 2.1.1, build 212 (ActiveState)
Python 2.1.1 (#20, Jul 26 2001, 11:38:51) [MSC 32 bit 
(Intel)] on win32
Type "copyright", "credits" or "license" for more 
information.
>>> a=1.#asdf
>>> a
1.0
>>> a=2.#INF
>>> a
2.0
-----------

It seems like this notation should either be 
disallowed totally, or at least be disallowed when it 
does not result in a valid IEEE magic number (as in 
the second and third examples).

Also, maybe this has an impact on pickling if IEEE 
magic numbers cannot be remade from their strings, e.g.

>>> x=1e300
>>> y=x*x
>>> y
1.#INF
>>> z=float(str(y))
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
ValueError: invalid literal for float(): 1.#INF

(Note that "float()" does not accept the "#" notation, 
but the parser does.)

thanks,

=g2

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>Comment By: Grant Griffin (dspguru)
Date: 2001-11-14 10:35

Message:
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Oops!  Sorry about that guys!

I guess I forgot about the comment thing.  (Must be doing 
too much C++ lately <wink>.)

=g2

----------------------------------------------------------------------

Comment By: Tim Peters (tim_one)
Date: 2001-11-14 10:17

Message:
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Not a bug:  as Michael said, "#" is Python's comment 
character.  See the Reference Manual for Python's grammar 
for float literals.

BTW, I expect you're running on Windows, as I don't know of 
any other system that spells infinity as "1.#INF".  float
("1.#INF") fails on Windows because Microsoft's C floating 
input routines don't accept it (although Microsoft's C 
floating output routines produce it).  Other platforms are 
much better behaved in this respect (they can read what 
they write).

Beyond all that, Python has no knowledge of 754 gimmicks.  
Repairing that is a feature request in PEP 42; that's a 
major project (IMO), but with no volunteers in sight.

----------------------------------------------------------------------

Comment By: Michael Hudson (mwh)
Date: 2001-11-14 10:07

Message:
Logged In: YES 
user_id=6656

You haven't forgotten the fact that # is the comment
character in Python, have you?

This makes it "tricky" to implement reading

1.#INF

as anything other than 

1.

!

----------------------------------------------------------------------

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