On Sat, 15 Apr 2017 10:23 am, bartc wrote: > On 15/04/2017 00:40, Rick Johnson wrote:
>> * `range(10)` will always produce a list of the _same_ 10 >> integers. > > You don't know if 'range' is still a range. If this has been executed > first, then the answer will be 20: > > oldrange=range > def double(x): return oldrange(x*2) > range=double Correct. It is true that *at the moment* CPython doesn't know if range has been shadowed or redefined, but Victor Stinner is working on a project, FATPython, which will. Or at least, FATPython can tell: - there's no chance that range() has been redefined, so it is safe to optimize the call to it; - or there is a chance, in which case it is not safe to optimize. >> * `for i in range(10)` will aways iterate over the _same_ >> 10 integers > > And range could be set to something else each time the loop is executed. It could, but that won't effect the loop. py> old_range = range py> for i in range(5): ... range = i*100 ... print(i) ... 0 1 2 3 4 py> range 400 >> * `answer += 1` will always increment the "current integer >> value" by 1 > > I don't know if it's possible to override __iadd__ for integers so that > +=1 does something different here. No, Python doesn't allow the built-in types to be monkey-patched. However, that's not the problem. The problem is that CPython doesn't know whether answer is a built-in int or not until runtime. -- Steve “Cheer up,” they said, “things could be worse.” So I cheered up, and sure enough, things got worse. -- https://mail.python.org/mailman/listinfo/python-list
