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Update postfix_evaluation.py

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Christian Clauss 2023-08-23 14:25:18 +02:00 committed by GitHub
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data_structures/stacks/postfix_evaluation.py
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@ -1,5 +1,5 @@
"""
The Reverse Polish Nation also known as Polish postfix notation or simply postfix
Reverse Polish Nation is also known as Polish postfix notation or simply postfix
notation.
https://en.wikipedia.org/wiki/Reverse_Polish_notation
Classic examples of simple stack implementations.
@ -39,13 +39,13 @@ OPERATORS = {
def parse_token(token: str | float) -> float | str:
"""
Converts the given data to appropriate number if it is indeed a number, else returns
the data as it is with a False flag. This function also serves as a check of whether
the input is a number or not.
Converts the given data to the appropriate number if it is indeed a number, else
returns the data as it is with a False flag. This function also serves as a check
of whether the input is a number or not.
Parameters
----------
token: The data which needs to be converted to the appropriate operator or number.
token: The data that needs to be converted to the appropriate operator or number.
Returns
-------
@ -63,7 +63,7 @@ def parse_token(token: str | float) -> float | str:
def evaluate(post_fix: list[str], verbose: bool = False) -> float:
"""
Function that evaluates postfix expression using a stack.
Evaluate postfix expression using a stack.
>>> evaluate(["0"])
0.0
>>> evaluate(["-0"])
@ -95,11 +95,11 @@ def evaluate(post_fix: list[str], verbose: bool = False) -> float:
Parameters
----------
post_fix : list
The postfix expression tokenized into operators and operands and stored as a
python list
post_fix:
The postfix expression is tokenized into operators and operands and stored
as a Python list
verbose : bool
verbose:
Display stack contents while evaluating the expression if verbose is True
Returns
@ -129,7 +129,7 @@ def evaluate(post_fix: list[str], verbose: bool = False) -> float:
)
continue
# If x is operator
# If only 1 value is inside stack and + or - is encountered
# If only 1 value is inside the stack and + or - is encountered
# then this is unary + or - case
if x in UNARY_OP_SYMBOLS and len(stack) < 2:
b = stack.pop() # pop stack
@ -175,12 +175,12 @@ def evaluate(post_fix: list[str], verbose: bool = False) -> float:
if verbose:
# output in tabular format
print(
str(x).rjust(8),
f"{x}".rjust(8),
f"push({a}{x}{b})".ljust(12),
stack,
sep=" | ",
)
# If everything executed correctly, the stack will contain
# If everything is executed correctly, the stack will contain
# only one element which is the result
if len(stack) != 1:
raise ArithmeticError("Input is not a valid postfix expression")