On Sun, 28 Aug 2011 00:19:07 -0400 Terry Reedy <tjre...@udel.edu> wrote:
> On 8/27/2011 11:45 PM, John O'Hagan wrote: > > Somewhat apropos of the recent "function principle" thread, I was recently > > surprised by this: > > > > funcs=[] > > for n in range(3): > > def f(): > > return n > > funcs.append(f) > > > > > > > > The last expression, IMO surprisingly, is [2,2,2], not [0,1,2]. [...] > > def f(): return n > is a CONSTANT value. It is not a closure. Quite right: I originally encountered this inside a function, but removed the enclosing function to show the issue in minimal form. > Your code above is the same as > def f(): return n > funcs = [f,f,f] > n = 2 > [i() for i in funcs] > Also right, but I still find this surprising. [...] > > > My question is, is this an inescapable consequence of using closures, > > I cannot answer since I am not sure what you mean by 'this'. Ah, but you are and you have: > Closures are nested functions that access the locals of enclosing > functions. To ensure that the access remains possible even after the > enclosing function returns, the last value of such accessed names is > preserved even after the enclosing function returns. (That is the tricky > part.) > Thanks, John -- http://mail.python.org/mailman/listinfo/python-list
