Python Removing list element while iterating over list

Question

I m iterating over a list of elements in Python  do some action on it  and then remove them if they meet certain criteria   for element in somelist      do action element      if check element           remove element from list   What should I use in place of remove element  I have seen similar questions asked  but notice the presence of the do action part that is to be executed for all elements and thus eliminates the solution of using filters

User · Answer

Not exactly in-place  but some idea to do it   a     a    b    def inplace a       c          while len a   gt  0          e   a pop 0          if e     b               c append e      a extend c    You can extend the function to call you filter in the condition

User · Answer

To meet these criteria  modify original list in situ  no list copies  only one pass  works  a traditional solution is to iterate backwards   for i in xrange len somelist  - 1  -1  -1       element   somelist i      do action element      if check element           del somelist i    Bonus  Doesn t do len somelist  on each iteration  Works on any version of Python  at least as far back as 1 5 2      s xrange range  for 3 X   Update  If you want to iterate forwards  it s possible  just trickier and uglier   i   0 n   len somelist  while i  lt  n      element   somelist i      do action element      if check element           del somelist i          n   n - 1     else          i   i   1

User · Answer

List comp   results    x for x in  do action element  for element in somelist  if check element

User · Answer

Why not rewrite it to be   for element in somelist      do action element     if check element        remove element from list   See this question for how to remove from the list  though it looks like you ve already seen that Remove items from a list while iterating  Another option is to do this if you really want to keep this the same  newlist       for element in somelist      do action element        if not check element          newlst append element

User · Answer

You could always iterate over a copy of the list  leaving you free to modify the original   for item in list somelist           somelist remove item

User · Answer

Another way of doing so is   while i lt len your list       if  condition           del your list i      else          i  1   So  you delete the elements side by side while checking

User · Answer

You can still use filter  moving to an outside function the element modification  iterating just once   def do the magic x       do action x      return check x     you can get a different filtered list filter do the magic yourList     or have it modified in place  as suggested by Steven Rumbalski  see comment  yourList      itertools ifilter do the magic  yourList

User · Answer

You can make a generator that returns everything that isn t removed   def newlist somelist       for element in somelist          do action element          if not check element               yield element

User · Answer

for element in somelist      do action element  somelist       x for x in somelist if not check x     If you really need to do it in one pass without copying the list  i 0 while i  lt  len somelist       element   somelist i       do action element      if check element           del somelist i      else          i  1

[python] Python: Removing list element while iterating over list

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