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Updated postfix_evaluation.py to support Unary operators and floating point numbers Fixes #8754 and #8724
Also merged evaluate_postfix_notations.py and postfix_evaluation.py into postfix_evaluation.py Signed-off-by: Arijit De <arijitde2050@gmail.com>
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Arijit De
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@ -1,52 +0,0 @@
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"""
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The Reverse Polish Nation also known as Polish postfix notation
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or simply postfix notation.
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https://en.wikipedia.org/wiki/Reverse_Polish_notation
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Classic examples of simple stack implementations
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Valid operators are +, -, *, /.
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Each operand may be an integer or another expression.
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"""
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from __future__ import annotations
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from typing import Any
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def evaluate_postfix(postfix_notation: list) -> int:
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"""
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>>> evaluate_postfix(["2", "1", "+", "3", "*"])
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9
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>>> evaluate_postfix(["4", "13", "5", "/", "+"])
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6
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>>> evaluate_postfix([])
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0
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"""
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if not postfix_notation:
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return 0
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operations = {"+", "-", "*", "/"}
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stack: list[Any] = []
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for token in postfix_notation:
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if token in operations:
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b, a = stack.pop(), stack.pop()
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if token == "+":
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stack.append(a + b)
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elif token == "-":
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stack.append(a - b)
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elif token == "*":
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stack.append(a * b)
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else:
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if a * b < 0 and a % b != 0:
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stack.append(a // b + 1)
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else:
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stack.append(a // b)
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else:
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stack.append(int(token))
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return stack.pop()
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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@ -1,4 +1,11 @@
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"""
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The Reverse Polish Nation also known as Polish postfix notation
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or simply postfix notation.
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https://en.wikipedia.org/wiki/Reverse_Polish_notation
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Classic examples of simple stack implementations
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Valid operators are +, -, *, /.
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Each operand may be an integer or another expression.
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Output:
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Enter a Postfix Equation (space separated) = 5 6 9 * +
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@ -20,49 +27,167 @@ Enter a Postfix Equation (space separated) = 5 6 9 * +
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import operator as op
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def solve(post_fix):
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def get_number(data: str) -> [bool, int, float, str]:
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"""
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Converts the given data to appropriate number if it is indeed a number, else returns the data as it is with a False
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flag. This function also serves as a check of whether the input is a number or not.
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Parameters
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----------
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data : str
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The data which needs to be converted to the appropriate number
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Returns
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-------
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bool, int or float
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Returns a tuple of (a, b) where a is True if data is indeed a number (integer or numeric) and b is either an
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integer of a floating point number. If a is False, then b is 'data'
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"""
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try:
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val = int(data)
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return True, val
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except ValueError:
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try:
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val = float(data)
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return True, val
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except ValueError:
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return False, data
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def is_operator(data: str) -> bool:
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"""
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Checks whether a given input is one of the valid operators or not. Valid operators being '-', '+', '*', '^' and '/'.
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Parameters
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----------
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data : str
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The value that needs to be checked for operator
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Returns
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-------
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bool
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True if data is an operator else False.
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"""
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if data in ['-', '+', '*', '^', '/']:
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return True
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else:
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return False
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def evaluate(post_fix: list, verbose: bool = False) -> int:
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"""
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Function that evaluates postfix expression using a stack.
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>>> evaluate(["2", "1", "+", "3", "*"])
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9
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>>> evaluate(["4", "13", "5", "/", "+"])
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6
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>>> evaluate(["2", "-", "3", "+"])
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1
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>>> evaluate([])
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0
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Parameters
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----------
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post_fix : list
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The postfix expression tokenized into operators and operands and stored as a python list
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verbose : bool
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Display stack contents while evaluating the expression if verbose is True
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Returns
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-------
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int
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The evaluated value
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"""
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stack = []
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div = lambda x, y: int(x / y) # noqa: E731 integer division operation
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opr = {
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"^": op.pow,
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"*": op.mul,
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"/": div,
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"+": op.add,
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"-": op.sub,
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"^": lambda p, q: p ** q,
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"*": lambda p, q: p * q,
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"/": lambda p, q: p / q,
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"+": lambda p, q: p + q,
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"-": lambda p, q: p - q,
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} # operators & their respective operation
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# print table header
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print("Symbol".center(8), "Action".center(12), "Stack", sep=" | ")
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print("-" * (30 + len(post_fix)))
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if verbose:
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# print table header
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print("Symbol".center(8), "Action".center(12), "Stack", sep=" | ")
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print("-" * (30 + len(post_fix)))
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for x in post_fix:
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if x.isdigit(): # if x in digit
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is_number, x = get_number(x)
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if is_number: # if x is a number (integer, float)
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stack.append(x) # append x to stack
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# output in tabular format
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print(x.rjust(8), ("push(" + x + ")").ljust(12), ",".join(stack), sep=" | ")
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if verbose:
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# output in tabular format
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print(str(x).rjust(8), ("push(" + str(x) + ")").ljust(12), stack, sep=" | ")
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elif is_operator(x):
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# If only 1 value is inside stack and + or - is encountered, then this is unary + or - case
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if x in ['-', '+'] and len(stack) < 2:
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b = stack.pop() # pop stack
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if x == '-':
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stack.append(-b) # negate b and push again into stack
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else: # when x is unary +
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stack.append(b)
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if verbose:
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# output in tabular format
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print("".rjust(8), ("pop(" + str(b) + ")").ljust(12), stack, sep=" | ")
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print(str(x).rjust(8), ("push(" + str(x) + str(b) + ")").ljust(12), stack, sep=" | ")
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else:
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b = stack.pop() # pop stack
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if verbose:
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# output in tabular format
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print("".rjust(8), ("pop(" + str(b) + ")").ljust(12), stack, sep=" | ")
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a = stack.pop() # pop stack
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if verbose:
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# output in tabular format
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print("".rjust(8), ("pop(" + str(a) + ")").ljust(12), stack, sep=" | ")
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stack.append(opr[x](a, b)) # evaluate the 2 values popped from stack & push result to stack
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if verbose:
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# output in tabular format
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print(str(x).rjust(8), ("push(" + str(a) + str(x) + str(b) + ")").ljust(12), stack, sep=" | ")
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else:
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b = stack.pop() # pop stack
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# output in tabular format
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print("".rjust(8), ("pop(" + b + ")").ljust(12), ",".join(stack), sep=" | ")
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print(f"{x} is neither a number, nor a valid operator")
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break
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if len(stack) == 1: # If everything executed correctly, the stack will contain only one element which is the result
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_, result = get_number(stack[0])
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else:
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result = None
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return result
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a = stack.pop() # pop stack
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# output in tabular format
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print("".rjust(8), ("pop(" + a + ")").ljust(12), ",".join(stack), sep=" | ")
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stack.append(
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str(opr[x](int(a), int(b)))
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) # evaluate the 2 values popped from stack & push result to stack
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# output in tabular format
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print(
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x.rjust(8),
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("push(" + a + x + b + ")").ljust(12),
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",".join(stack),
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sep=" | ",
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)
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def is_yes(val: str) -> bool:
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"""
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Function that checks whether a user has entered any representation of a Yes (y, Y).
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Any other input is considered as a No.
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return int(stack[0])
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Parameters
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-----------
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val : str
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The value entered by user
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Returns
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-------
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bool
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True if Yes, otherwise False
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"""
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if val in ['Y', 'y']:
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return True
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else:
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return False
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if __name__ == "__main__":
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Postfix = input("\n\nEnter a Postfix Equation (space separated) = ").split(" ")
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print("\n\tResult = ", solve(Postfix))
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loop = True
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while loop: # Creating a loop so that user can evaluate postfix expression multiple times
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expression = input("Enter a Postfix Equation (space separated) For Example: 5 6 9 * +\n: ").split(" ")
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choice = input("Do you want to see stack contents while evaluating? [y/N]: ")
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display = is_yes(choice)
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output = evaluate(expression, display)
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if output is not None:
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print("Result = ", output)
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choice = input("Do you want to enter another expression? [y/N]: ")
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loop = is_yes(choice)
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