how to explain such codes, python's bug or mine?
>>> j = range(20) >>> print j [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19] >>> for k in j: if k <= 10: j.remove(k) >>> print j [1, 3, 5, 7, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19] >>> Python 2.3.4 (#53, May 25 2004, 21:17:02) [MSC v.1200 32 bit (Intel)] on win32 Type "copyright", "credits" or "license()" for more information. i think python do convert there codes to such style: for (i = 0; i < len(j); i++) k = j[i] .. what do u think? -- http://mail.python.org/mailman/listinfo/python-list
Re: how to explain such codes, python's bug or mine?
yes. i think it does so. it take me the whole afternoon to find out the bug (mine) i change: for i in range(len(j) -1, -1, -1): d = j[i] if d <= 10: j.remove(d) the real code is not so simple,so j[11:] will not work for me. but, i think phthon could found that i remove the current element, why it does not move the pointer automatically? for python, i am a newbie, but i did not found the warning of such usage from the python tutorial <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > Hi, > > it is not python bug. > You refer the list j and remove the element in the same time, that is > the problem. Python dinamicaly goes to the next element with the same > index but apply it in the new list. > > use this code instead: > j = range(20) > print j > L = [x for x in j if x > 10] > print L > > Sincerely Yours, > Pujo > -- http://mail.python.org/mailman/listinfo/python-list
Re: how to explain such codes, python's bug or mine?
SORRY, my inattention "Fredrik Lundh" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > "MaHahaXixi" <[EMAIL PROTECTED]> wrote: > > > for python, i am a newbie, but i did not found the warning of such usage > > from the python tutorial > > "4.2 for Statements" > > "It is not safe to modify the sequence being iterated over in the loop (this > can only happen for mutable sequence types, such as lists). If you need > to modify the list you are iterating over (for example, to duplicate selected > items) you must iterate over a copy." (followed by an example) > > > > > -- http://mail.python.org/mailman/listinfo/python-list
Re: how to explain such codes, python's bug or mine?
yes. i understand now. but i use another trick. list is in vary size, so i do not wanna copy it. "Jim" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > MaHahaXixi wrote: > >>>>j = range(20) > >>>>print j > > > > [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19] > > > >>>>for k in j: > > > > if k <= 10: > > j.remove(k) > > > > > > > >>>>print j > > > > [1, 3, 5, 7, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19] > > > > > > > > Python 2.3.4 (#53, May 25 2004, 21:17:02) [MSC v.1200 32 bit (Intel)] on > > win32 > > Type "copyright", "credits" or "license()" for more information. > > > > i think python do convert there codes to such style: > > for (i = 0; i < len(j); i++) > >k = j[i] > >.. > > > what do u think? > > > > > > I'm not quite sure of your question but with the second style you're not > attempting to change the original list but make a copy. That's perfectly > easy to do in Python as it is. The exampmle is a cautionary one about > changing the list on which you are iterating. > > Jim -- http://mail.python.org/mailman/listinfo/python-list
Re: how to explain such codes, python's bug or mine?
yes, i use the 2th way <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > Hi > > The second style can be used: >j = range(20) > print j > L = [x for x in j if x > 10] > j = L > > There are another method such poping the item based on last index to 0: > for i in range(len(j)-1,0-1,-1): > if j[i]<=10: > j.pop(i) > > print j > > Pujo > -- http://mail.python.org/mailman/listinfo/python-list
