Question

1. The Operand Stack - opstack The operand stack should be implemented as a Python list. The list will contain Python integers, strings, and later in Part 2 code arrays. Python integers and lists on the stack represent Postscript integer constants and array constants. Python strings which start with a slash / on the stack represent names of Postscript variables. When using a list as a stack, assume that the top of the stack is the end of the list (i.e., the pushing and popping happens at the end of the list).

The operand stack: define the operand stack and its operations opstack = [ ] #assuming top of the stack is the end of the list # Now define the helper functions to push and pop values on the opstack # (i.e, add/remove elements to/from the end of the Python list) # Remember that there is a Postscript operator called "pop" so we choose # different names for these functions. # Recall that `pass` in python is a no-op: replace it with your code.

def opPop():

pass

# opPop should return the popped value. # The pop() function should call opPop to pop the top value from the opstack, but it will ignore the popped value.

def opPush(value):

pass

Answer 1

SOURCE CODE IN PYTHON:

opStack=[] #list to act as stack

def opPop(): #function to pop the top of the stack
global opStack
if len(opStack)==0: #if stack is empty
return None
else:
pop=opStack[len(opStack)-1] #popping the top
opStack=opStack[:len(opStack)-1] #removing the top
return pop #return top

def opPush(value): #function to push a value into the stack
global opStack
opStack.append(value) #appending value to top of stack
  
def opPrint(): #function to print the stack
global opStack
for i in opStack:
print(i,end=' ')
print()
  
#testing the functions
opPush(1) #stack is now 1
print('1 pushed!')
opPush(2) #stack is now 1 2
print('2 pushed!')
opPush(3) #stack is now 1 2 3
print('3 pushed!')
print('Stack currently:')
opPrint()
value=opPop() #stack is now 1 2
if value==None:
print('Stack underflow!')
else:
print(value,'popped!')
print('Stack currently:')
opPrint()

OUTPUT: