Why do python lists have pop but not push

Question

Does anyone know why Python s list append function is not called list push given that there s already a list pop that removes and returns the last element  that indexed at -1  and list append semantic is consistent with that use

User · Answer

Ok  personal opinion here  but Append and Prepend imply precise positions in a set   Push and Pop are really concepts that can be applied to either end of a set    Just as long as you re consistent    For some reason  to me  Push   seems like it should apply to the front of a set

User · Answer

Not an official answer by any means  just a guess based on using the language   but Python allows you to use lists as stacks  e g   section 5 1 1 of the tutorial   However  a list is still first of all a list  so the operations that are common to both use list terms  i e   append  rather than stack terms  i e   push   Since a pop operation isn t that common in lists  though  removeLast  could have been used   they defined a pop   but not a push

User · Answer

Push and Pop make sense in terms of the metaphor of a stack of plates or trays in a cafeteria or buffet  specifically the ones in type of holder that has a spring underneath so the top plate is  more or less    in theory  in the same place no matter how many plates are under it     If you remove a tray  the weight on the spring is a little less and the stack  pops  up a little  if you put the plate back  it  push es the stack down   So if you think about the list as a stack and the last element as being on top  then you shouldn t have much confusion

User · Answer

Because it appends an element to a list  Push is usually used when referring to stacks

User · Answer

Because  append  intuitively means  add at the end of the list   If it was called  push   then it would be unclear whether we re adding stuff at the tail or at head of the list

User · Answer

Because it appends  it doesn t push   Appending  adds to the end of a list   pushing  adds to the front   Think of a queue vs  a stack   http   docs python org tutorial datastructures html  Edit  To reword my second sentence more exactly   Appending  very clearly implies adding something to the end of a list  regardless of the underlying implementation  Where a new element gets added when it s  pushed  is less clear  Pushing onto a stack is putting something on  top   but where it actually goes in the underlying data structure completely depends on implementation  On the other hand  pushing onto a queue implies adding it to the end

User · Answer

FYI  it s not terribly difficult to make a list that has a push method    gt  gt  gt  class StackList list           def push self  item                   self append item        gt  gt  gt  x   StackList  1 2 3    gt  gt  gt  x  1  2  3   gt  gt  gt  x push 4   gt  gt  gt  x  1  2  3  4    A stack is a somewhat abstract datatype   The idea of  pushing  and  popping  are largely independent of how the stack is actually implemented   For example  you could theoretically implement a stack like this  although I don t know why you would    l    1 2 3  l insert 0  1  l pop 0       and I haven t gotten into using linked lists to implement a stack

User · Answer

Push is a defined stack behaviour  if you pushed A on to stack  B C D  you would get  A B C D    If you used python append  the resulting dataset would look like  B C D A   Edit  Wow  holy pedantry   I would assume that it would be clear from my example which part of the list is the top  and which part is the bottom  Assuming that most of us here read from left to right  the first element of any list is always going to be on the left

User · Answer

Probably because the original version of Python  CPython  was written in C  not C     The idea that a list is formed by pushing things onto the back of something is probably not as well-known as the thought of appending them

User · Answer

Because  append  existed long before  pop  was thought of  Python 0 9 1 supported list append in early 1991  By comparison  here s part of a discussion on comp lang python about adding pop in 1997  Guido wrote      To implement a stack  one would need   to add a list pop   primitive   and   no  I m not against this particular   one on the basis of any  principle      list push   could be added for   symmetry with list pop    but I m not   a big fan of multiple names for the   same operation --  sooner or later   you re going to read code that uses   the other one  so  you need to learn   both  which is more cognitive load    You can also see he discusses the idea of if push pop put pull should be at element  0  or after element  -1  where he posts a reference to Icon s list      I stil think that all this is best   left out of the list object    implementation -- if you need a stack    or a queue  with particular    semantics  write a little class that   uses a lists   In other words  for stacks implemented directly as Python lists  which already supports fast append    and del list -1   it makes sense that list pop   work by default on the last element  Even if other languages do it differently   Implicit here is that most people need to append to a list  but many fewer have occasion to treat lists as stacks  which is why list append came in so much earlier

[python] Why do python lists have pop() but not push()

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