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] [] -- http://mail.python.org/mailman/listinfo/python-list