Hi David,
Thank you for your answer and suggestions. It was really helpful.
10 Şubat 2020 Pazartesi 02:12:34 UTC+3 tarihinde David Bailey yazdı:
>
> On 09/02/2020 18:52, Barış Bulut wrote:
>
> x,y = symbols('x,y')
>
> y = x**3
> y.subs(x,5)
> 125
>
> x = 5
> y.subs(x,x)
> x**3
> y.subs(x,10)
> x**3
> y.subs(x,3)
> x**3
>
> x = 3
> y.subs(x,125)
> x**125
> y.subs(x,10)
> x**10
>
>
> Hi Barış,
>
> It isn't a bug!
>
> Unfortunately as soon as you execute x=5 you destroy the symbol in x,
> replacing it by 5 .
>
> That means that y.subs(x,10) becomes
>
> (x**3).subs(5,3)
>
> No replacements are possible, so this return x**3
>
> Then you set x to 3 so that y.subs(x,125) becomes
>
> (x**3).subs(3,125) which yields
>
> x**125
>
> etc.
>
> The correct code would be
>
> x=symbols('x')
>
> y=x**3
>
> y.subs(x,5)
>
> y.subs(x,10)
>
> etc.
>
> Notice that y never needed to be a variable, because you never used it - y
> got overwritten just as x did.
>
> If you want to store an expression like x**3 in a python variable, I find
> it useful to use a longer name that wouldn't normally be used in a
> mathematical expression. If you set up a variable as a symbol, then it is
> best not to assign to it later until perhaps you understand what is going
> on.
>
> Cheers,
>
> David
>
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