If I do from __future__ import division then eval(1/2) gives me 0.5 as
expected. But if I do print input("enter a sum: ") and enter 1/2 as
the sum I get 0 as if I hadn't done the import. I thought input was
supposed to give the same behaviour as an eval on raw input -- why the
difference here?
12  2122 
Try 1.0/2 instead of 1/2. Note that when I do eval("1/2") I get 0 not
0.5
-Denis
Le Sun, 11 Jan 2004 23:45:48 +0000, Tim Rowe
<tim@remove_if_ not_spam.digiti g.co.uk> a écrit : If I do from __future__ import division then eval(1/2) gives me 0.5 as
expected. But if I do print input("enter a sum: ") and enter 1/2 as
the sum I get 0 as if I hadn't done the import. I thought input was
supposed to give the same behaviour as an eval on raw input -- why the
difference here?
Denis Sarrazin wrote: Try 1.0/2 instead of 1/2. Note that when I do eval("1/2") I get 0 not
0.5
Please note: "from __future__ import division", see PEP 238 which
changes the behavior of the divisino operator.
My results with Python 2.3.3:
from __future__ import division
eval('1/2')
0.5 input()
1/2
0 eval(raw_input( ))
1/2
0.5
-Denis
Le Sun, 11 Jan 2004 23:45:48 +0000, Tim Rowe
<tim@remove_if_ not_spam.digiti g.co.uk> a écrit :
If I do from __future__ import division then eval(1/2) gives me 0.5 as
expected. But if I do print input("enter a sum: ") and enter 1/2 as
the sum I get 0 as if I hadn't done the import. I thought input was
supposed to give the same behaviour as an eval on raw input -- why the
difference here?
Tim Rowe <tim@remove_if_ not_spam.digiti g.co.uk> writes: If I do from __future__ import division then eval(1/2) gives me 0.5 as
expected. But if I do print input("enter a sum: ") and enter 1/2 as
the sum I get 0 as if I hadn't done the import. I thought input was
supposed to give the same behaviour as an eval on raw input -- why the
difference here?
The input function is calling eval from the context of the module
where 'input' itself is defined. If you use "from __future__ import
division" in module A and have "print 3/2" in module B, the value of
3/2 in module B shouldn't be affected by the input, since module B
may depend on integer division having the old behavior.
The result is a little bit surprising at first glance though, so it
should probably be documented.
In article <7x************ @ruckus.brouhah a.com>, Paul Rubin <http@?.cx>
writes Tim Rowe <tim@remove_if_ not_spam.digiti g.co.uk> writes: If I do from __future__ import division then eval(1/2) gives me 0.5 as
expected. But if I do print input("enter a sum: ") and enter 1/2 as
the sum I get 0 as if I hadn't done the import. I thought input was
supposed to give the same behaviour as an eval on raw input -- why the
difference here?
The input function is calling eval from the context of the module
where 'input' itself is defined. If you use "from __future__ import
division" in module A and have "print 3/2" in module B, the value of
3/2 in module B shouldn't be affected by the input, since module B
may depend on integer division having the old behavior.
The result is a little bit surprising at first glance though, so it
should probably be documented.
I get this in pythonwin with 2.3.2
PythonWin 2.3.2 (#49, Oct 2 2003, 20:02:00) [MSC v.1200 32 bit (Intel)]
on win32.
Portions Copyright 1994-2001 Mark Hammond (mh******@skipp inet.com.au) -
see 'Help/About PythonWin' for further copyright information. from __future__ import division
eval('1/2')
0.5
In python I get
Python 2.3.2 (#49, Oct 2 2003, 20:02:00) [MSC v.1200 32 bit (Intel)] on
win32
Type "help", "copyright" , "credits" or "license" for more information. from __future__ import division
eval('1/2')
0.5
so I guess pythonwin is broken in this respect.
--
Robin Becker
[Tim Rowe] If I do from __future__ import division then eval(1/2) gives me 0.5 as
expected. But if I do print input("enter a sum: ") and enter 1/2 as
the sum I get 0 as if I hadn't done the import. I thought input was
supposed to give the same behaviour as an eval on raw input -- why the
difference here?
[Paul Rubin[ The input function is calling eval from the context of the module
where 'input' itself is defined. If you use "from __future__ import
division" in module A and have "print 3/2" in module B, the value of
3/2 in module B shouldn't be affected by the input, since module B
may depend on integer division having the old behavior.
Right!
So, the way to get eval() to respond to the import is to pass along
the current environment:
from __future__ import division
eval('9/2', globals())
4.5
Raymond Hettinger
Robin Becker <ro***@jessikat .fsnet.co.uk> writes: Python 2.3.2 (#49, Oct 2 2003, 20:02:00) [MSC v.1200 32 bit (Intel)] on
win32
Type "help", "copyright" , "credits" or "license" for more information. from __future__ import division
eval('1/2') 0.5
so I guess pythonwin is broken in this respect.
Huh? you get the expected result with both python and pythonwin. Neither
one is broken. The surprising result is from input(), not eval():
$ python
Python 2.2.2 (#1, Feb 24 2003, 19:13:11)
[GCC 3.2.2 20030222 (Red Hat Linux 3.2.2-4)] on linux2
Type "help", "copyright" , "credits" or "license" for more information. from __future__ import division
print input('expressi on: ')
expression: 1/2
0 print eval('1/2')
0.5
That's because input evaluates its string in the context of a
different module which was compiled with old-style division. I don't
know of other functions that use eval like that, and input() should
be deprecated or eliminated anyway, so this isn't a big deal.
Thanks. I'd not realized that we could test out new changes to Python
within existing Python code. Cool.
-D
Le Mon, 12 Jan 2004 02:49:45 -0700, Jason Mobarak <jm**@unm.edu > a
écrit : Please note: "from __future__ import division", see PEP 238 which
changes the behavior of the divisino operator. py****@rcn.com (Raymond Hettinger) writes: [Tim Rowe] If I do from __future__ import division then eval(1/2) gives me 0.5 as
expected. But if I do print input("enter a sum: ") and enter 1/2 as
the sum I get 0 as if I hadn't done the import. I thought input was
supposed to give the same behaviour as an eval on raw input -- why the
difference here?
[Paul Rubin[ The input function is calling eval from the context of the module
where 'input' itself is defined. If you use "from __future__ import
division" in module A and have "print 3/2" in module B, the value of
3/2 in module B shouldn't be affected by the input, since module B
may depend on integer division having the old behavior.
Right!
So, the way to get eval() to respond to the import is to pass along
the current environment:
from __future__ import division
eval('9/2', globals())
4.5
Um, that's not how it works. Off the top of my head I'm not entirely
sure why eval() respects future statements and input() does not, but
it's probably easy enough to fix, if anyone cares (I don't think I
do).
Cheers,
mwh
--
Windows 2000: Smaller cow. Just as much crap. -- Jim's pedigree of
operating systems, asr
In article <7x************ @ruckus.brouhah a.com>, Paul Rubin <http@?.cx>
writes Robin Becker <ro***@jessikat .fsnet.co.uk> writes: Python 2.3.2 (#49, Oct 2 2003, 20:02:00) [MSC v.1200 32 bit (Intel)] on
win32
Type "help", "copyright" , "credits" or "license" for more information. >>> from __future__ import division
>>> eval('1/2')
0.5 >>>
I guess I'm 'broken' :)
--
Robin Becker This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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