Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p><strong>Polymorphic Tree Walking</strong>, Python version</p> <pre><code>#!/usr/bin/python class Node: """base class, you should not process one of these""" def process(self): raise('you should not be processing a node') class BinaryNode(Node): """base class for binary nodes""" def __init__(self, _left, _right): self.left = _left self.right = _right def process(self): raise('you should not be processing a binarynode') class Plus(BinaryNode): def process(self): return self.left.process() + self.right.process() class Minus(BinaryNode): def process(self): return self.left.process() - self.right.process() class Mul(BinaryNode): def process(self): return self.left.process() * self.right.process() class Div(BinaryNode): def process(self): return self.left.process() / self.right.process() class Num(Node): def __init__(self, _value): self.value = _value def process(self): return self.value def demo(n): print n.process() demo(Num(2)) # 2 demo(Plus(Num(2),Num(5))) # 2 + 3 demo(Plus(Mul(Num(2),Num(3)),Div(Num(10),Num(5)))) # (2 * 3) + (10 / 2) </code></pre> <p>The tests are just building up the binary trees by using constructors.</p> <p>program structure:</p> <p>abstract base class: Node</p> <ul> <li>all Nodes inherit from this class</li> </ul> <p>abstract base class: BinaryNode</p> <ul> <li>all binary operators inherit from this class</li> <li>process method does the work of evaluting the expression and returning the result</li> </ul> <p>binary operator classes: Plus,Minus,Mul,Div</p> <ul> <li>two child nodes, one each for left side and right side subexpressions</li> </ul> <p>number class: Num</p> <ul> <li>holds a leaf-node numeric value, e.g. 17 or 42</li> </ul>
    singulars
    1. This table or related slice is empty.
    1. POExpression Evaluation and Tree Walking using polymorphism? (ala Steve Yegge)
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USMark Harrison
    1. USMark Harrison
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POExpression Evaluation and Tree Walking using polymorphism? (ala Steve Yegge)
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. COThis answer is horribly over-engineered. The question was for 2 + (2), not an arbitrary arithmetic calculation. Also, this just executes the tree, it doesn't build it.
      singulars
      1. PO
      1. USReaperUnreal
    2. COThe question was for an arithmetic calculation SUCH AS 2 + (2), not the calculation of 2 + (2). Therefore, it's not over-engineered, but answers the question as intended.
      singulars
      1. PO
      1. USThomas Owens
    3. COThis answer is not to the question of "How do you go from an arithmetic expression (e.g. in a STRING) such as "2 + (2)".... Where does "demo(Plus(Mul(Num(2),Num(3)),Div(Num(10),Num(5))))" come from? That other program we don't get to see? Why is this marked as best answer?
      singulars
      1. PO
      1. USGuge
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload