Different ways of clearing lists

Question

Is there any reason to do anything more complicated than one of these two lines when you want to clear a list in Python   old list      old list   list     The reason I ask is that I just saw this in some running code   del old list  0 len old list

User · Answer

Doing alist      does not clear the list  just creates an empty list and binds it to the variable alist  The old list will still exist if it had other variable bindings   To actually clear a list in-place  you can use any of these ways    alist clear      Python 3 3   most obvious del alist    alist         alist    0       fastest   See the Mutable Sequence Types documentation page for more details

User · Answer

There are two cases in which you might want to clear a list    You want to use the name old list further in your code  You want the old list to be garbage collected as soon as possible to free some memory    In case 1 you just go on with the assigment       old list           or whatever you want it to be equal to   In case 2 the del statement would reduce the reference count to the list object the name old list points at  If the list object is only pointed by the name old list at  the reference count would be 0  and the object would be freed for garbage collection       del old list

User · Answer

del list       Will delete the values of that list variable   del list   Will delete the variable itself from memory

User · Answer

If you re clearing the list  you  obviously  don t need the list anymore  If so  you can just delete the entire list by simple del method   a    1  3  5  6  del a   This will entirely delete a the list     But in case  you need it again  you can reinitialize it  Or just simply clear its elements by   del a

User · Answer

There is a very simple way to clear a python list  Use del list name      For example    gt  gt  gt  a    1  2  3   gt  gt  gt  b   a  gt  gt  gt  del a     gt  gt  gt  print a  b

User · Answer

another solution that works fine is to create empty list as a reference empty list   empt list        for example you have a list as   a list    1 2 3   To clear it just make the following   a list   list empt list    this will make a list an empty list just like the empt list

User · Answer

It appears to me that del will give you the memory back  while assigning a new list will make the old one be deleted only when the gc runs matter   This may be useful for large lists  but for small list it should be negligible   Edit  As  Algorias  it doesn t  matter   Note that   del old list  0 len old list      is equivalent to  del old list

User · Answer

Clearing a list in place will affect all other references of the same list   For example  this method doesn t affect other references    gt  gt  gt  a    1  2  3   gt  gt  gt  b   a  gt  gt  gt  a       gt  gt  gt  print a      gt  gt  gt  print b   1  2  3    But this one does    gt  gt  gt  a    1  2  3   gt  gt  gt  b   a  gt  gt  gt  del a           equivalent to   del a 0 len a    gt  gt  gt  print a      gt  gt  gt  print b      gt  gt  gt  a is b True   You could also do    gt  gt  gt  a

[python] Different ways of clearing lists

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