a *= b not equivalent to a = a*b

[mlz]

Partly it's the layout, but mathematically speaking the two should be equal.

(a*b)/c should equal a*(b/c)

The fact that they're not is surprising, because python 2 so seamlessly supports big integers in a mathematically correct way.

I consider such surprising behavior to be abstraction leak, which is probably why it has been fixed in python 3.

  -= m =-


On Friday, August 26, 2016 at 12:54:02 AM UTC-7, Erik wrote:
> On 26/08/16 08:14, mlz wrote:
> >
> > I was being facetious, but behind it is a serious point. Neither the APL nor the J languages use precedence even though their inventor, Ken Iverson, was a mathematician.
> >
> > That was to support functional programming dating back to the 1970's.
> 
> Precedence is not the issue here anyway. Both '*' and '/' have the same 
> precedence. The two operations in your expressions have to be evaluated 
> in SOME order - either left-to-right or right-to-left.
> 
> 
> The issue is twofold:
> 
> Firstly, the compound assignments will always evaluate their RHS before 
> performing the assignment - this is not the same as operator precedence 
> - they have to, else what does Python pass to the function that knows 
> what the compound assignment means for that type (e.g. sequences may be 
> extended for '*=')? So for compound assignments there is always 
> effectively an implicit set of parentheses around the RHS compared to 
> the expression without the assignment operator (if you think of the 
> compound assignment as being a _part_ of the overall expression).
> 
> Secondly, the way you have chosen to layout your code has fooled your 
> brain into thinking that the division is performed before the 
> multiplication. Python doesn't care that you jammed the sub-expression 
> together with no whitespace ;)
> 
> E.