This is done so that the instruction stream can be read off a network connection, for instance. POP Discard the object on the stack top. DUP Push the object on the stack top onto the stack. NONE Push the object 'None' onto the stack. INT value Push the integer 'value' onto the stack.
LONG value Push the long integer 'value' onto the stack.
MARK Push a unique 'marker' onto the stack. Markers are used to create tuples, lists etc. without having to specify a count. Everything up to and including the marker is removed from the stack and the new tuple is pushed onto it. Everything up to and including the marker is removed from the stack and the new list is pushed onto it. Everything up to and including the marker is removed from the stack and the new dictionary is pushed onto it.