Re: overload builtin operator
Robert Kern wrote: Shaun wrote: Thanks for your replies, obviously this isn't a simple thing to do so I'll take a different tack. The exact problem I am trying to solve here is to avoid the ZeroDivisionError in division. I have c++ code which delegates to python to calculate expressions on table cells. The values of the table cell are arbitary numbers and the expressions to be calculated are fairly simple python arithmetic and math functions. The problem being that some users want an expression like '(100/x)+ 3' where x=0 to return 3. So that dividing a number by zero results in 0. You have silly users. You mean you don't? Damn. Can I have some of yours? Iain -- http://mail.python.org/mailman/listinfo/python-list
Re: overload builtin operator
Iain King wrote: Robert Kern wrote: You have silly users. You mean you don't? Damn. Can I have some of yours? No, you may not. Mine! All mine! -- Robert Kern [EMAIL PROTECTED] In the fields of hell where the grass grows high Are the graves of dreams allowed to die. -- Richard Harter -- http://mail.python.org/mailman/listinfo/python-list
Re: overload builtin operator
On Sun, 28 Aug 2005 23:27:07 -0400, Terry Reedy [EMAIL PROTECTED] wrote: I suspect that PyPy, when further alone, will make it easier to do things like develop a customized interpreter that has alternate definitions for builtin operators. So maybe the OP should ask again in a year or two. OTOH, did you notice that I provided (although I didn't post the underlying walker framework) a way (that works now) of importing a module with the / operator effectively converted to a safediv call, as the OP apparently wanted? ;-) BTW, I posted an update that handles non-simple-name-target /= augassigns as well, but though it shows on google groups, I can't see it yet. Still some news server problem, apparently. Or maybe it's just slogging to catch up after previous problem... Regards, Bengt Richter -- http://mail.python.org/mailman/listinfo/python-list
Re: overload builtin operator
On Sun, 28 Aug 2005 04:09:10 GMT, [EMAIL PROTECTED] (Bengt Richter) wrote:
[... a response to the OP's apparent desire to overload the divide operator
with a call
to his safediv function ...]
The part that rewrote the the AugAssign could only work for plain name
Augassign targets, so
I introduced a helper function to generate a suitable assignment target node
for attributes,
subscripts, and slices as well. So the test (still very alpha) looks like the
following now:
testdiv.py
-
def test():
print 1.0/2.0
print 12/3
a=12; b=3
print a/b
print 2**a/(b+1)
try:
print 'print 1/0 ='
print 1/0
except Exception, e: print '%s: %s' %(e.__class__.__name__, e)
try:
print 'print a/(b*(a-12)) ='
print a/(b*(a-12))
except Exception, e: print '%s: %s' %(e.__class__.__name__, e)
try:
print 'def foo(x=1/(b-3)): return x ='
def foo(x=1/(b-3)): return x
print 'print foo() ='
print foo()
except Exception, e: print '%s: %s' %(e.__class__.__name__, e)
try:
print 'b /= (a-12) ='
b /= (a-12)
print 'b after b/=(a-12):', b
except Exception, e: print '%s: %s' %(e.__class__.__name__, e)
print 's=[15]; s[0] /= 3; print s ='
s=[15]; s[0] /= 3; print s
class T(list):
def __getitem__(self, i): print i; return 42
def __setitem__(self, i, v): print i, v
def __div__(self, other): print self, other; return 4242
t = T()
print 't.x=15; t.x /= 3; print t.x ='
t.x=15; t.x /= 3; print t.x
print 't=T([15, 27]); t /= 3; print t ='
t=T([15, 27]); t /= 3; print t
def foo(x, y):
for dis.dis to show code
z = x/y
x /= y
x.a /= y
x[z] /= y
x[:] /= y
if __name__ == '__main__': test()
--
Outputfrom run without conversion of / :
import_safediv.py
--
# import_safediv.py
from arborist import import_editing_ast, get_augassign_tgt
from compiler.ast import Div, CallFunc, Name, AugAssign, Assign
def safediv(num, den):
if den==0: result = 0*num
else: result = num/den
print 'safediv(%r, %r) = %r'%(num, den, result)
return result
def div2safediv(divnode):
replace Div nodes with CallFunc nodes calling safediv with same args
return CallFunc(Name('safediv'),[divnode.left, divnode.right], None, None,
divnode.lineno)
def divaugass2safediv(auganode):
if auganode.op != '/=': return auganode
return Assign([get_augassign_tgt(auganode)],
CallFunc(Name('safediv'),[auganode.node, auganode.expr], None, None,
auganode.lineno))
callbacks = {Div:div2safediv, AugAssign:divaugass2safediv}
def import_safediv(modname, verbose=False):
modsafe = import_editing_ast(modname, callbacks, verbose)
modsafe.safediv = safediv
return modsafe
if __name__ == '__main__':
modsafe = import_safediv('testdiv', verbose=True)
modsafe.test()
---
Result from using the above interactively:
[14:21] C:\pywk\ut\astpy24
Python 2.4b1 (#56, Nov 3 2004, 01:47:27)
[GCC 3.2.3 (mingw special 20030504-1)] on win32
Type help, copyright, credits or license for more information.
First import as usual and run test()
import testdiv
testdiv.test()
0.5
4
4
1024
print 1/0 =
ZeroDivisionError: integer division or modulo by zero
print a/(b*(a-12)) =
ZeroDivisionError: integer division or modulo by zero
def foo(x=1/(b-3)): return x =
ZeroDivisionError: integer division or modulo by zero
b /= (a-12) =
ZeroDivisionError: integer division or modulo by zero
s=[15]; s[0] /= 3; print s =
[5]
t.x=15; t.x /= 3; print t.x =
5
t=T([15, 27]); t /= 3; print t =
[15, 27] 3
4242
Now import the import_safediv importer, to import with
conversion of ast to effect translation of divides to safediv calls:
Import and runs test() much as before:
from import_safediv import import_safediv
tdsafe = import_safediv('testdiv')
tdsafe.test()
safediv(1.0, 2.0) = 0.5
0.5
safediv(12, 3) = 4
4
safediv(12, 3) = 4
4
safediv(4096, 4) = 1024
1024
print 1/0 =
safediv(1, 0) = 0
0
print a/(b*(a-12)) =
safediv(12, 0) = 0
0
def foo(x=1/(b-3)): return x =
safediv(1, 0) = 0
print foo() =
0
b /= (a-12) =
safediv(3, 0) = 0
b after b/=(a-12): 0
s=[15]; s[0] /= 3; print s =
safediv(15, 3) = 5
[5]
t.x=15; t.x /= 3; print t.x =
safediv(15, 3) = 5
5
t=T([15, 27]); t /= 3; print t =
[15, 27] 3
safediv([15, 27], 3) = 4242
4242
Look at the code generated by normal import first
import dis
dis.dis(testdiv.foo)
40 0 LOAD_FAST0 (x)
3 LOAD_FAST1 (y)
6 BINARY_DIVIDE
7 STORE_FAST 2
Re: overload builtin operator
I suspect that PyPy, when further alone, will make it easier to do things like develop a customized interpreter that has alternate definitions for builtin operators. So maybe the OP should ask again in a year or two. TJR -- http://mail.python.org/mailman/listinfo/python-list
Re: overload builtin operator
On Thu, 25 Aug 2005 16:12:20 +0200, Reinhold Birkenfeld [EMAIL PROTECTED]
wrote:
Shaun wrote:
Hi,
I'm trying to overload the divide operator in python for basic arithmetic.
eg. 10/2 ... no classes involved.
I am attempting to redefine operator.__div__ as follows:
# my divide function
def safediv(a,b):
return ...
# reassign buildin __div__
import operator
operator.__div__ = safediv
The operator.__dict__ seems to be updated OK but the '/' operator still
calls buildin __div__
It won't work that way. You cannot globally modify the behaviour of an
operator,
but you can customize how an operator works for your type.
Consider:
class safeint(int):
def __div__(self, other):
return safediv(self, other)
safeint(10)/2
You are right that you cannot globally modify the behaviour of an operator in
the
sense the OP seems to be envisioning, but with some trouble I think it would be
possible
to interfere with the translation of 'numerator-term/denominator-term' to
become
'safediv(numerator-term, denominator-term)' by transforming the AST during
a custom
import process, such that wherever a Div node is found, a CallFunc node is
substituted. E.g.,
for a node like
Div((Name('numerator'), Name('denominator')))
substitute another node like
CallFunc(Name('safediv'), [Name('numerator'), Name('denominator')], None,
None)
where the Name('numerator') and Name('denominator') in the latter are actually
the Div node's .left and .right, so as to operate on the same args (which can
be abitrary expression-representing subtrees).
Of course, you probably also want to replace
AugAssign(Name('a'), '/=', Name('b'))
with
Assign([AssName('a', 'OP_ASSIGN')], CallFunc(Name('safediv'), [Name('a'),
Name('b')], None, None))
Unfortunately, the AST tree does not seem to be designed to be edited easily wrt
_replacing_ nodes found by walking via flattened lists vs. just _using_ them in
order.
I think I can create special walker that can do replacements of nodes found
anywhere, and
calling node-type-specific or default supplied callbacks to supply replacements
for original nodes
passed to them, but this will require a number of specialized visitor methods
etc., so I will
have to get back to this later. But at least the OP and you nudged me into
thinking about
AST rewriting again ;-) (also affects my @@sourcedeco ideas ;-)
... this didn't go out due to news server problem, so I'll add some clips from
what I did re ast editing:
testdiv.py
-
def test():
print 1.0/2.0
print 12/3
a=12; b=3
print a/b
print 2**a/(b+1)
try:
print 'print 1/0 ='
print 1/0
except Exception, e: print '%s: %s' %(e.__class__.__name__, e)
try:
print 'print a/(b*(a-12)) ='
print a/(b*(a-12))
except Exception, e: print '%s: %s' %(e.__class__.__name__, e)
try:
print 'def foo(x=1/(b-3)): return x ='
def foo(x=1/(b-3)): return x
print 'print foo() ='
print foo()
except Exception, e: print '%s: %s' %(e.__class__.__name__, e)
try:
print 'b /= (a-12) ='
b /= (a-12)
print 'b after b/=(a-12):', b
except Exception, e: print '%s: %s' %(e.__class__.__name__, e)
if __name__ == '__main__': test()
---
Outputfrom run without conversion of / :
0.5
4
4
1024
print 1/0 =
ZeroDivisionError: integer division or modulo by zero
print a/(b*(a-12)) =
ZeroDivisionError: integer division or modulo by zero
def foo(x=1/(b-3)): return x =
ZeroDivisionError: integer division or modulo by zero
b /= (a-12) =
ZeroDivisionError: integer division or modulo by zero
import_safediv.py
--
# import_safediv.py
from importast import importast
from compiler.ast import Div, CallFunc, Name
from compiler.ast import AugAssign, Assign, AssName
def safediv(num, den):
if den==0: result = 0*num
else: result = num/den
print 'safediv(%r, %r) = %r'%(num, den, result)
return result
def div2safediv(divnode):
replace Div nodes with CallFunc nodes calling safediv with same args
return CallFunc(Name('safediv'),[divnode.left, divnode.right], None, None,
divnode.lineno)
def divaugass2safediv(auganode):
if auganode.op != '/=': return auganode
assname =auganode.node.name
return Assign([AssName(assname, 'OP_ASSIGN')],
CallFunc(Name('safediv'),[Name(assname), auganode.expr], None, None,
auganode.lineno))
callbacks = {Div:div2safediv, AugAssign:divaugass2safediv}
def import_safediv(modname, verbose=False):
return importast(modname, callbacks, verbose)
if __name__ == '__main__':
import sys
modname, args = sys.argv[1], sys.argv[2:]
verbose = (args[0:] and args[0]=='-verbose') or False
Re: overload builtin operator
Thanks for your replies, obviously this isn't a simple thing to do so I'll take a different tack. The exact problem I am trying to solve here is to avoid the ZeroDivisionError in division. I have c++ code which delegates to python to calculate expressions on table cells. The values of the table cell are arbitary numbers and the expressions to be calculated are fairly simple python arithmetic and math functions. The problem being that some users want an expression like '(100/x)+ 3' where x=0 to return 3. So that dividing a number by zero results in 0. Apart from parsing the expression string myself and checking for divide by zero I can't find another way to solve the problem. Hopefully someone out there has some ideas. Thanks, Shaun. -- http://mail.python.org/mailman/listinfo/python-list
Re: overload builtin operator
Shaun wrote: Thanks for your replies, obviously this isn't a simple thing to do so I'll take a different tack. The exact problem I am trying to solve here is to avoid the ZeroDivisionError in division. I have c++ code which delegates to python to calculate expressions on table cells. The values of the table cell are arbitary numbers and the expressions to be calculated are fairly simple python arithmetic and math functions. The problem being that some users want an expression like '(100/x)+ 3' where x=0 to return 3. So that dividing a number by zero results in 0. You have silly users. There's only one place I can think of where division of a finite, nonzero number by zero can sensibly result in zero (underdetermined least squares via SVD). I'd be curious as to why they want that behavior. Apart from parsing the expression string myself and checking for divide by zero I can't find another way to solve the problem. It might be easier to parse the expression and wrap all of the numbers by a subclass of float that does division like you want. -- Robert Kern [EMAIL PROTECTED] In the fields of hell where the grass grows high Are the graves of dreams allowed to die. -- Richard Harter -- http://mail.python.org/mailman/listinfo/python-list
overload builtin operator
Hi, I'm trying to overload the divide operator in python for basic arithmetic. eg. 10/2 ... no classes involved. I am attempting to redefine operator.__div__ as follows: # my divide function def safediv(a,b): return ... # reassign buildin __div__ import operator operator.__div__ = safediv The operator.__dict__ seems to be updated OK but the '/' operator still calls buildin __div__ Does anyone know if this is possible and if I'm going along the correct path with my attempts above? Is it possible to do this using a C extention? Regards, Shaun. -- http://mail.python.org/mailman/listinfo/python-list
Re: overload builtin operator
Shaun wrote: Hi, I'm trying to overload the divide operator in python for basic arithmetic. eg. 10/2 ... no classes involved. I am attempting to redefine operator.__div__ as follows: # my divide function def safediv(a,b): return ... # reassign buildin __div__ import operator operator.__div__ = safediv The operator.__dict__ seems to be updated OK but the '/' operator still calls buildin __div__ It won't work that way. You cannot globally modify the behaviour of an operator, but you can customize how an operator works for your type. Consider: class safeint(int): def __div__(self, other): return safediv(self, other) safeint(10)/2 Reinhold -- http://mail.python.org/mailman/listinfo/python-list
