59 lines
1.8 KiB
Python
59 lines
1.8 KiB
Python
class StackUnderflowError(Exception):
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pass
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def is_integer(string):
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try:
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int(string)
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return True
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except ValueError:
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return False
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def evaluate(input_data):
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if not input_data:
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return []
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defines = {}
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while input_data[0][:1] == ':':
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values = input_data.pop(0).split()
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values.pop()
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values.pop(0)
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key = values.pop(0).lower()
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if is_integer(key):
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raise ValueError("Integers cannot be redefined")
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defines[key] = values
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stack = []
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input_data = input_data[-1].split()
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while any(input_data):
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word = input_data.pop(0).lower()
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try:
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if is_integer(word):
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stack.append(int(word))
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elif word in defines:
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input_data = defines[word] + input_data
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elif word == '+':
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stack.append(stack.pop() + stack.pop())
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elif word == '-':
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stack.append(-stack.pop() + stack.pop())
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elif word == '*':
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stack.append(stack.pop() * stack.pop())
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elif word == '/':
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divisor = stack.pop()
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if divisor == 0:
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raise ZeroDivisionError("Attempted to divide by zero")
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stack.append(int(stack.pop() / divisor))
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elif word == 'dup':
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stack.append(stack[-1])
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elif word == 'drop':
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stack.pop()
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elif word == 'swap':
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stack.append(stack[-2])
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del stack[-3]
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elif word == 'over':
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stack.append(stack[-2])
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else:
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raise ValueError("{} has not been defined".format(word))
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except IndexError:
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raise StackUnderflowError("Insufficient number of items in stack")
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return stack
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