Object-Oriented Design Frequently Asked Questions

Python

How does one check whether an object `c` is of "type" `C` ?

If the object c is a literal and the type C a builtin type (such as an int) which cannot be instantiated, then the test
```
    c == int(c)
```
can for example be used (as in the Roman Numeral example).
If the object is not a literal type, one can explicitly query the object's type. This is done by loading the module types and using the type() operator.
```
 
    import types
    type(1) == types.IntType
    
```
To check what the pre-defined basic types are:
```
    dir(types) 
```
If the object c is however an instance of a class, and we want to check if c is an instance of class C, we can use the test
```
    isinstance(c, C)
```
This will evaluate to True (1) if c is an instance of class C or any of C's sub-classes.
In recent versions of Python, it is possible to test for basic types with isinstance as in isinstance(1,int), isinstance(1.2,float) and isinstance([1,2],list).

How do I generate nice HTML from Python source code ?

Colorized pretty-printing for file code.py can be done with
```
enscript -Whtml -Epython --color code.py -o code.html
```
An API document for file code.py can be generated with
```
pydoc -w code
```

Assignments

What are the algorithms needed to evaluate() a spreadsheet ?

The topological sort and strong component algorithms are given here in pseudo-code. More details (on for example algorithm complexity) are found in the literature.

MUST we work in teams of 2 ?

You must work in a team of exactly two people. Previous experience has shown that after the initial transient chaos of finding a partner, this works really well. Try to find a team partner after class. Remember that "pair programming" requires you to actually work together (same place, same time). You may form different teams for different assignments.

Typos in assignment 1

There are several typos on the assignment 1 design drawing.

In the CellRef class, the evalutate() method should obviously read evaluate().
In that same CellRef class, the __isRelative attribute should be called __refKind instead. In the text also, all isRelative occurrences should be changed to refKind. If isRelative were used, it would make sense for it to be of Boolean type. refKind is a string which takes either the "ABSOLUTE" or "RELATIVE" value.