title: Infix to postfix algorithm in python
body: <p>For my data structures class I have to create a basic graphing calculator using Python 3. The requirement is that we have to use a basic Stack class. The user enters the equation in "infix" form which I'm then supposed to convert to "postfix" for evaluation and graphing. I'm having trouble with the infix to postfix algorithm. I've seen other algorithms that can work but my professor wants it done a certain way. Here's what I have so far:</p>
  
  <pre><code>def inFixToPostFix():
  inFix = '3*(x+1)-2/2'
  postFix = ''
  s = Stack()
  for c in inFix:
      # if elif chain for anything that c can be
      if c in "0123456789x":
          postFix += c
      elif c in "+-":
          if s.isEmpty():
              s.push(c)
          elif s.top() =='(':
              s.push(c)
      elif c in "*/":
          if s.isEmpty():
              s.push(c)
          elif s.top() in "+-(":
              s.push(c)
      elif c == "(":
          s.push(c)
      elif c == ")":
          while s.top() is not '(':
              postFix += s.pop()
          s.pop()
      else:
          print("Error")
  print(postFix)
  return postFix
  </code></pre>
  
  <p>When I print this i get '3x1+22' when the expected result is '3x1+*22/-'
  Any help would be appreciated. Thanks.</p>