deref in a string into an operand

[John Doe]

I've got the action '+' stored as the variable 'plus',
that is plus='+'

Now I want to use the variable plus in an equation:
5 plus 7, just line 5 + 7

How do I do that?

Dan

[John Doe]

Re: deref in a string into an operand

Foolish me; I examined the __builtin__ and found __getattribute_ _,
along with '__mul__' '__add__', '__sub__' and '__div__'.

So using a builtin object like 'x' ...

x = 5
attr = '__mul__'

print x.__getattribut e__( attr )( 5 )
25

My program will store the operand as '__mul__' instead of '*', along with
a health bit of comment.

Dan. Closed.

On Fri, 05 Nov 2004 08:01:59 +0000, John Doe wrote:
[color=blue]
> I've got the action '+' stored as the variable 'plus',
> that is plus='+'
>
> Now I want to use the variable plus in an equation:
> 5 plus 7, just line 5 + 7
>
> How do I do that?
>
> Dan[/color]

[Peter Otten]

Re: deref in a string into an operand

John Doe wrote:
[color=blue]
> Foolish me; I examined the __builtin__ and found __getattribute_ _,
> along with '__mul__' '__add__', '__sub__' and '__div__'.
>
> So using a builtin object like 'x' ...
>
> x = 5
> attr = '__mul__'
>
> print x.__getattribut e__( attr )( 5 )
> 25
>
> My program will store the operand as '__mul__' instead of '*', along with
> a health bit of comment.[/color]

However, this may sometimes fail:
[color=blue][color=green][color=darkred]
>>> 1 + 1.0[/color][/color][/color]
2.0[color=blue][color=green][color=darkred]
>>> 1 .__add__(1.0)[/color][/color][/color]
NotImplemented

Consider using the operator module instead:
[color=blue][color=green][color=darkred]
>>> import operator
>>> operator.add(1, 1.0)[/color][/color][/color]
2.0[color=blue][color=green][color=darkred]
>>> getattr(operato r, "add")(1, 1.0)[/color][/color][/color]
2.0

Peter

[Steven Bethard]

Re: deref in a string into an operand

John Doe <atterdan <at> yahoo.com> writes:[color=blue]
>
> So using a builtin object like 'x' ...
>
> x = 5
> attr = '__mul__'
>
> print x.__getattribut e__( attr )( 5 )
> 25
>
> My program will store the operand as '__mul__' instead of '*', along with
> a health bit of comment.[/color]

You also might consider just storing the operator.<op> methods in an appropriate
dictionary:
[color=blue][color=green][color=darkred]
>>> import operator
>>> operator_map = {'+':operator.a dd, '-':operator.sub}
>>> operator_map['+'](1, 2.0)[/color][/color][/color]
3.0

This allows you to call the add function whatever you want.

Steve

[Peter Abel]

Re: deref in a string into an operand

John Doe <atterdan@yahoo .com> wrote in message news:<pan.2004. 11.05.08.00.19. 364836@yahoo.co m>...[color=blue]
> I've got the action '+' stored as the variable 'plus',
> that is plus='+'
>
> Now I want to use the variable plus in an equation:
> 5 plus 7, just line 5 + 7
>
> How do I do that?
>
> Dan[/color]

If you want a string:
equation = '5 '+plus+' 7'

or

equation = '5 %s 7' % plus

Regards
Peter