pro2 solved

Author: yyl

unit3/input2.txt

@@ -0,0 +1,2 @@
++ * + 5 9 2 * 6 5 =
+/ + 5 5.5 1.5 * - 6 5 2 = 

unit3/output.txt

@@ -1,5 +1,2 @@
-38.0
-10.5
-33.75
-25.0
-0.0
+58.0
+0.142857142857

unit3/pro2.py

@@ -0,0 +1,104 @@
+'''
+RPN Calculator
+Modify Program  so that it accepts expressions written in prefix (Polish) notation
+'''
+
+from opus7.stackAsLinkedList import StackAsLinkedList
+
+class Algorithms(object):
+
+  def __init__(self):
+    self.stack = StackAsLinkedList()
+
+  def calculator(self, input, output):
+    for line in input.readlines():
+      # prefix is acrtually the reversed version of postfix
+      line = line.split()
+      operation = line[:-1]
+      operation.reverse()
+      operation.append(line[-1])
+      for word in operation:
+        if word == "+":
+          print "it is +"
+          arg2 = self.stack.pop()
+          arg1 = self.stack.pop()
+          self.stack.push(arg1 + arg2)
+        elif word == "*":
+          print "it is *"
+          arg2 = self.stack.pop()
+          arg1 = self.stack.pop()
+          self.stack.push(arg1 * arg2)
+        elif word == "-":
+          print "it is -"
+          arg2 = self.stack.pop()
+          arg1 = self.stack.pop()
+          self.stack.push(arg1 - arg2)
+        elif word == "/":
+          print "it is /"
+          arg2 = self.stack.pop()
+          arg1 = self.stack.pop()
+          self.stack.push(arg1 / arg2)
+        # exponential expression
+        elif word == "^":
+          print "it is ^"
+          arg2 = self.stack.pop()
+          arg1 = self.stack.pop()
+          self.stack.push(arg1 ** arg2)
+        elif word == "=":
+          print "it is ="
+          arg = self.stack.pop()
+          output.write(str(arg) + "\n")
+          print "ans is ", arg
+        else:
+          print "it is number"
+          # make it double
+          self.stack.push(float(word))	
+	'''
+    def operating(a2, a1, word):
+        print "operating: ", a2, a1, word
+        if word == "+":
+          print "it is +"
+          return a2 + a1
+        elif word == "*":
+          print "it is *"
+          return a2 * a1
+        elif word == "-":
+          print "it is -"
+          return a2 - a1
+        elif word == "/":
+          print "it is /"
+          return a2 / a1
+        # exponential expression
+        elif word == "^":
+          print "it is ^"
+          return a2 ** a1
+        else:
+          print "unrecognizable"
+          # make it double
+    operators = ["+", "-", "*", "/", "^"]
+    for line in input.readlines():
+      for word in line.split():
+        if word in operators:
+          print "push operator " + word
+          self.stack.push(word)
+        elif word == "=":
+          arg = self.stack.pop()
+          output.write(str(arg) + "\n")
+          print "ans = ", arg
+        else:
+          print "push number " + word
+          flag = 0
+          if self.stack.getTop() not in operators:
+            flag = 1
+          self.stack.push(float(word))
+          if flag == 1:
+            arg2 = self.stack.pop()
+            arg1 = self.stack.pop()
+            oper = self.stack.pop()
+            self.stack.push(operating(arg2, arg1, oper))
+            print "push answer"
+			'''
+		
+a = Algorithms()
+a.calculator(open("input2.txt", 'r'), open("output.txt", 'w+'))
+