Is there a simple way to delete a list element by value

Question

I want to remove a value from a list if it exists in the list  which it may not   a    1  2  3  4  b   a index 6   del a b  print a   The above case  in which it does not exist  shows the following error  Traceback  most recent call last     File  quot D  zjm code a py quot   line 6  in  lt module gt      b   a index 6  ValueError  list index x   x not in list  So I have to do this  a    1  2  3  4   try      b   a index 6      del a b  except      pass  print a   But is there not a simpler way to do this

User · Answer

As stated by numerous other answers  list remove   will work  but throw a ValueError if the item wasn t in the list  With python 3 4   there s an interesting approach to handling this  using the suppress contextmanager   from contextlib import suppress with suppress ValueError       a remove  b

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With a for loop and a condition   def cleaner seq  value           temp                                for number in seq          if number    value              temp append number      return temp   And if you want to remove some  but not all   def cleaner seq  value  occ       temp          for number in seq          if number    value and occ              occ -  1             continue         else              temp append number      return temp

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Say for example  we want to remove all 1 s from x  This is how I would go about it   x    1  2  3  1  2  3    Now  this is a practical use of my method   def Function List  Unwanted        List remove Unwanted  for Item in range List count Unwanted        return List x   Function x  1  print x    And this is my method in a single line    x remove 1  for Item in range x count 1    print x    Both yield this as an output    2  3  2  3  2  3    Hope this helps   PS  pleas note that this was written in version 3 6 2  so you might need to adjust it for older versions

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This example is fast and will delete all instances of a value from the list   a    1 2 3 1 2 3 4  while True      try          a remove 3      except          break print a  gt  gt  gt   1  2  1  2  4

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Overwrite the list by indexing everything except the elements you wish to remove  gt  gt  gt  s    5 4 3 2 1   gt  gt  gt  s 0 2    s 3    5  4  2  1   More generally   gt  gt  gt  s    5 4 3 2 1   gt  gt  gt  i   s index 3   gt  gt  gt  s  i    s i 1    5  4  2  1

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In one line   a remove  b   if  b  in a else None   sometimes it usefull   Even easier   if  b  in a  a remove  b

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Finding a value in a list and then deleting that index  if it exists  is easier done by just using list s remove method    gt  gt  gt  a    1  2  3  4   gt  gt  gt  try        a remove 6      except ValueError        pass       gt  gt  gt  print a  1  2  3  4   gt  gt  gt  try        a remove 3      except ValueError        pass       gt  gt  gt  print a  1  2  4    If you do this often  you can wrap it up in a function   def remove if exists L  value     try      L remove value    except ValueError      pass

User · Answer

To remove an element s first occurrence in a list  simply use list remove    gt  gt  gt  a     a    b    c    d    gt  gt  gt  a remove  b    gt  gt  gt  print a    a    c    d     Mind that it does not remove all occurrences of your element  Use a list comprehension for that    gt  gt  gt  a    10  20  30  40  20  30  40  20  70  20   gt  gt  gt  a    x for x in a if x    20   gt  gt  gt  print a   10  30  40  30  40  70

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Another possibility is to use a set instead of a list  if a set is applicable in your application   IE if your data is not ordered  and does not have duplicates  then  my set set  3 4 2   my set discard 1    is error-free   Often a list is just a handy container for items that are actually unordered   There are questions asking how to remove all occurences of an element from a list   If you don t want dupes in the first place  once again a set is handy   my set add 3    doesn t change my set from above

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this is my answer  just use while and for  def remove all data  value       i   j   0     while j  lt  len data           if data j     value              j    1             continue         data i    data j          i    1         j    1     for x in range j - i           data pop

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Usually Python will throw an Exception if you tell it to do something it can t so you ll have to do either   if c in a      a remove c    or   try      a remove c  except ValueError      pass   An Exception isn t necessarily a bad thing as long as it s one you re expecting and handle properly

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Maybe your solutions works with ints  but It Doesnt work for me with dictionarys   In one hand  remove   has not worked for me  But maybe it works with basic Types  I guess the code bellow is also the way to remove items from objects list   In the other hand   del  has not worked properly either  In my case  using python 3 6  when I try to delete an element from a list in a  for  bucle with  del  command  python changes the index in the process and bucle stops prematurely before time  It only works if You delete element by element in reversed order  In this way you dont change the pending elements array index when you are going through it  Then  Im used   c   len list -1 for element in  reversed list        if condition element           del list c      c -  1 print list    where  list  is like    key1  value1     key2  value2     key3  value3         Also You can do more pythonic using enumerate   for i  element in enumerate reversed list        if condition element           del list  i 1  -1  print list

User · Answer

Consider   a    1 2 2 3 4 5    To take out all occurrences  you could use the filter function in python  For example  it would look like   a   list filter lambda x  x   2  a     So  it would keep all elements of a    2   To just take out one of the items use   a remove 2

User · Answer

Here s how to do it inplace  without list comprehension    def remove all seq  value       pos   0     for item in seq          if item    value             seq pos    item            pos    1     del seq pos

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This removes all instances of  -v  from the array sys argv  and does not complain if no instances were found   while  -v  in sys argv      sys argv remove  -v     You can see the code in action  in a file called speechToText py     python speechToText py -v   speechToText py      python speechToText py -x   speechToText py    -x      python speechToText py -v -v   speechToText py      python speechToText py -v -v -x   speechToText py    -x

User · Answer

If you know what value to delete  here s a simple way  as simple as I can think of  anyway    a    0  1  1  0  1  2  1  3  1  4  while a count 1   gt  0      a remove 1    You ll get  0  0  2  3  4

User · Answer

You can do  a  1 2 3 4  if 6 in a      a remove 6    but above need to search 6 in list a 2 times  so try except would be faster  try      a remove 6  except      pass

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If your elements are distinct  then a simple set difference will do   c    1 2 3 4  x  8 6 7  x  9  x   z   list set c  - set   x     print z  1  2  3  4  6  7  8  9

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We can also use  pop    gt  gt  gt  lst    23 34 54 45   gt  gt  gt  remove element   23  gt  gt  gt  if remove element in lst          lst pop lst index remove element        23  gt  gt  gt  lst  34  54  45   gt  gt  gt

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list1  1 2 3 3 4 5 6 1 3 4 5   n int input  enter  number     while n in list1      list1 remove n   print list1

User · Answer

arr    1  1  3  4  5  2  4  3     to remove first occurence of that element  suppose 3 in this example arr remove 3     to remove all occurences of that element  again suppose 3   use something called list comprehension new arr    element for element in arr if element  3     if you want to delete a position use  pop  function  suppose    position 4    the pop function also returns a value removed element   arr pop 4     u can also use  del  to delete a position del arr 4

[python] Is there a simple way to delete a list element by value?

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