Data commit

Task/Parsing-RPN-to-infix-conversion/Python/parsing-rpn-to-infix-conversion.py

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+"""
+>>> # EXAMPLE USAGE
+>>> result = rpn_to_infix('3 4 2 * 1 5 - 2 3 ^ ^ / +', VERBOSE=True)
+TOKEN  STACK
+3      ['3']
+4      ['3', '4']
+2      ['3', '4', '2']
+*      ['3', Node('2','*','4')]
+1      ['3', Node('2','*','4'), '1']
+5      ['3', Node('2','*','4'), '1', '5']
+-      ['3', Node('2','*','4'), Node('5','-','1')]
+2      ['3', Node('2','*','4'), Node('5','-','1'), '2']
+3      ['3', Node('2','*','4'), Node('5','-','1'), '2', '3']
+^      ['3', Node('2','*','4'), Node('5','-','1'), Node('3','^','2')]
+^      ['3', Node('2','*','4'), Node(Node('3','^','2'),'^',Node('5','-','1'))]
+/      ['3', Node(Node(Node('3','^','2'),'^',Node('5','-','1')),'/',Node('2','*','4'))]
++      [Node(Node(Node(Node('3','^','2'),'^',Node('5','-','1')),'/',Node('2','*','4')),'+','3')]
+"""
+
+prec_dict =  {'^':4, '*':3, '/':3, '+':2, '-':2}
+assoc_dict = {'^':1, '*':0, '/':0, '+':0, '-':0}
+
+class Node:
+    def __init__(self,x,op,y=None):
+        self.precedence = prec_dict[op]
+        self.assocright = assoc_dict[op]
+        self.op = op
+        self.x,self.y = x,y
+
+    def __str__(self):
+        """
+        Building an infix string that evaluates correctly is easy.
+        Building an infix string that looks pretty and evaluates
+        correctly requires more effort.
+        """
+        # easy case, Node is unary
+        if self.y == None:
+            return '%s(%s)'%(self.op,str(self.x))
+
+        # determine left side string
+        str_y = str(self.y)
+        if  self.y < self or \
+            (self.y == self and self.assocright) or \
+            (str_y[0] is '-' and self.assocright):
+
+            str_y = '(%s)'%str_y
+        # determine right side string and operator
+        str_x = str(self.x)
+        str_op = self.op
+        if self.op is '+' and not isinstance(self.x, Node) and str_x[0] is '-':
+            str_x = str_x[1:]
+            str_op = '-'
+        elif self.op is '-' and not isinstance(self.x, Node) and str_x[0] is '-':
+            str_x = str_x[1:]
+            str_op = '+'
+        elif self.x < self or \
+             (self.x == self and not self.assocright and \
+              getattr(self.x, 'op', 1) != getattr(self, 'op', 2)):
+
+            str_x = '(%s)'%str_x
+        return ' '.join([str_y, str_op, str_x])
+
+    def __repr__(self):
+        """
+        >>> repr(Node('3','+','4')) == repr(eval(repr(Node('3','+','4'))))
+        True
+        """
+        return 'Node(%s,%s,%s)'%(repr(self.x), repr(self.op), repr(self.y))
+
+    def __lt__(self, other):
+        if isinstance(other, Node):
+            return self.precedence < other.precedence
+        return self.precedence < prec_dict.get(other,9)
+
+    def __gt__(self, other):
+        if isinstance(other, Node):
+            return self.precedence > other.precedence
+        return self.precedence > prec_dict.get(other,9)
+
+    def __eq__(self, other):
+        if isinstance(other, Node):
+            return self.precedence == other.precedence
+        return self.precedence > prec_dict.get(other,9)
+
+
+
+def rpn_to_infix(s, VERBOSE=False):
+    """
+
+    converts rpn notation to infix notation for string s
+
+    """
+    if VERBOSE : print('TOKEN  STACK')
+
+    stack=[]
+    for token in s.replace('^','^').split():
+        if token in prec_dict:
+            stack.append(Node(stack.pop(),token,stack.pop()))
+        else:
+            stack.append(token)
+
+        # can't use \t in order to make global docstring pass doctest
+        if VERBOSE : print(token+' '*(7-len(token))+repr(stack))
+
+    return str(stack[0])
+
+strTest = "3 4 2 * 1 5 - 2 3 ^ ^ / +"
+strResult = rpn_to_infix(strTest, VERBOSE=False)
+print ("Input: ",strTest)
+print ("Output:",strResult)
+
+print()
+
+strTest = "1 2 + 3 4 + ^ 5 6 + ^"
+strResult = rpn_to_infix(strTest, VERBOSE=False)
+print ("Input: ",strTest)
+print ("Output:",strResult)