On Jun 7, 5:56 pm, John Machin <[EMAIL PROTECTED]> wrote: > On Jun 8, 6:05 am, [EMAIL PROTECTED] wrote: > > > > > On Jun 7, 2:42 pm, "Daniel Fetchinson" <[EMAIL PROTECTED]> > > wrote: > > > > > Hi. I'd like to port a Perl function that does something I don't > > > > know how to do in Python. (In fact, it may even be something that > > > > is distinctly un-Pythonic!) > > > > > The original Perl function takes a reference to an array, removes > > > > from this array all the elements that satisfy a particular criterion, > > > > and returns the list consisting of the removed elements. Hence > > > > this function returns a value *and* has a major side effect, namely > > > > the target array of the original argument will be modified (this > > > > is the part I suspect may be un-Pythonic). > > > > > Can a Python function achieve the same effect? If not, how would > > > > one code a similar functionality in Python? Basically the problem > > > > is to split one list into two according to some criterion. > > > > This function will take a list of integers and modify it in place such > > > that it removes even integers. The removed integers are returned as a > > > new list (disclaimer: I'm 100% sure it can be done better, more > > > optimized, etc, etc): > > > > def mod( alist ): > > > old = alist[:] > > > ret = [ ] > > > for i in old: > > > if i % 2 == 0: > > > ret.append( alist.pop( alist.index( i ) ) ) > > > > return ret > > > > x = range(10,20) > > > > print x > > > r = mod( x ) > > > print r > > > print x > > > > HTH, > > > Daniel > > > -- > > > Psss, psss, put it down! -http://www.cafepress.com/putitdown > > > def mod( alist ): > > return [ alist.pop( alist.index( x ) ) for x in alist if x % 2 == > > 0 ] > > > alist = range(10,20) > > blist = mod( alist ) > > > print alist > > print blist > > > The same thing with list comprehensions. > > Not the same. The original responder was careful not to iterate over > the list which he was mutating. > > >>> def mod(alist): > > ... return [alist.pop(alist.index(x)) for x in alist if x % 2 == 0] > ...>>> a = range(10) > >>> print mod(a), a > > [0, 2, 4, 6, 8] [1, 3, 5, 7, 9]>>> a = [2,2,2,2,2,2,2,2] > >>> print mod(a), a > > [2, 2, 2, 2] [2, 2, 2, 2] > # should be [2, 2, 2, 2, 2, 2, 2, 2] []
Alas, it appears my understanding of list comprehensions is significantly less comprehensive than I thought =) -- http://mail.python.org/mailman/listinfo/python-list
