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python_symb/parse.py

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+from __future__ import annotations
+from typing import List, Union
+from operator_file import Add, Mul, Min, BinOperator, UnaryOperator
+from symbols import Symbols, Var
+from fraction import Fraction
+
+x, y = Var('x'), Var('y')
+
+ParenthesisLeft = Symbols('(')
+ParenthesisRight = Symbols(')')
+
+Number = Union[int, float, Fraction]
+
+name_to_symbol = {sy.name:sy for sy in Symbols.instances}
+
+
+
+
+def update_symbols_dict():
+    global name_to_symbol
+    name_to_symbol = {sy.name:sy for sy in Symbols.instances}
+
+
+"""
+example1 = "a + b * c + d"
+-
+example2 = 2*x+3*y*(4+sin(5))
+-
+example3 = "(a + b) * (c + -d))"
+should return Tree(Expr('*', [Expr('+', [Expr('a'), Expr('b')]), Expr('+', [Expr('c'), Expr('-', [Expr('d')])])]))
+"""
+
+
+def preprocess(expr: str) -> List:
+    """
+    Preprocesses a string expression to a list of symbols and numbers
+    :param expr: string expression
+    :return: list of symbols and numbers
+    """
+    return_list = []
+    expr = expr.strip()
+    expr = expr.replace(' ', '')
+    m = max([len(sy) for sy in name_to_symbol.keys()])
+    i = 0
+    while i < len(expr):
+        found = False
+        for j in range(m, 0, -1):
+            word = expr[i:i+j]
+            if word in name_to_symbol or word.isdigit():
+                if word in name_to_symbol:
+                    return_list.append(name_to_symbol[word])
+                else:
+                    return_list.append(int(word))
+                i += j
+                found = True
+                break
+
+        if not found:
+            raise ValueError(f'Invalid expression: {expr} at index {i}\n')
+    return return_list
+
+
+def return_to_string(expr: List) -> str:
+    """
+    Returns a string expression from a list of symbols and numbers
+    :param expr: list of symbols and numbers
+    :return: string expression
+    """
+    return ' '.join([str(sy) for sy in expr])
+
+
+def infix_to_postfix(expr: List) -> List:
+    global ParenthesisLeft, ParenthesisRight
+    """
+    Converts an infix string expression (standard) to a postfix expression (reverse polish notation)
+    :param expr: infix expression
+    :return: postfix expression
+
+    use shunting yard algorithm
+    """
+    op_stack = []
+    postfix = []
+    for sy in expr:
+        match sy:
+            case int() | float() | Fraction() | Var():
+                postfix.append(sy)
+            case _ if sy == ParenthesisLeft:
+                op_stack.append(sy)
+            case _ if sy == ParenthesisRight:
+                while op_stack[-1] != ParenthesisLeft:
+                    postfix.append(op_stack.pop())
+                op_stack.pop()
+            case UnaryOperator():
+                op_stack.append(sy)
+
+            case BinOperator():
+                while op_stack and op_stack[-1] != ParenthesisLeft and op_stack[-1].precedence >= sy.precedence:
+                    postfix.append(op_stack.pop())
+                op_stack.append(sy)
+    while op_stack:
+        postfix.append(op_stack.pop())
+    return postfix
+
+
+def infix_str_to_postfix(expr):
+    return infix_to_postfix(preprocess(expr))
+
+
+if __name__ == "__main__":
+
+    expr = "(x+7)*y+sin(24-2*(1-5))"
+    prep = preprocess(expr)
+    print(prep)
+    post = infix_to_postfix(prep)
+    print(post)
+    print(return_to_string(post))
+
+
+
+
+