title: Testing for the existence of a field in a class
body: <p>i have a quick question. I have a 2D array that stores an instance of a class. The elements of the array are assigned a particular class based on a text file that is read earlier in the program. Since i do not know without looking in the file what class is stored at a particular element i could refer to a field that doesn't exist at that index (referring to appearance when an instance of temp is stored in that index). i have come up with a method of testing this, but it is long winded and requires a second matrix. Is there a function to test for the existence of a field in a class?</p>
  
  <pre><code>class temp():
     name = "default"
  
  class temp1():
     appearance = "@"
  </code></pre>