CS102: Introduction to Computer Science II

This video introduces the OO paradigm. The video mentions 4 modules: software engineering, signals, circuits, and planning. These modules focus on key concepts for building models for analyzing and solving problems that are applicable to many problems.

Our focus is on the software engineering module, which uses Python to illustrate the application of several concepts (modularity, abstraction, composition, and hierarchy) to programming as part of the OO paradigm. The video gives examples of data abstraction: using numbers and operations to form numeric expressions; strings and string operations to build string structures; and 'execution' abstraction (procedure names to represent sequences of instructions). Abstraction enables the composition of data to form more complex expressions and the composition of procedures to form hierarchies of procedures.

The video then shows how these two, data abstraction and procedure abstraction, are combined to form a composite structure, called a class, that consists of both data and procedures. An object is simply an instance of a class. A class contains the data and procedures common to the its instances, i.e. objects. An object consists of the class data, class procedures (called methods), assignment of values to the class (comm) data, and, can also include additional data and additional procedures. Just like data and procedures, classes and objects are given names, i.e. names are bound to them.

The video concludes with an explanation of how Python uses name bindings (the association of a name with a 'value' -- a data value, expression, or procedure, object, or class instructions) when it executes instructions. Name bindings are stored by Python in a table called an environment. Each procedure, each class, and each object has it own environment table. When a name is used in a procedure, Python looks up the name in the procedure's environment table to find the value associated with it. Since a Python name can be shared, for example, by a class and an object, rather than store the shared name twice the shared name is in the class environment and the object environment points to the class environment. Thus, a hierarchy of environments is used to represent a class – object hierarchy. The key concepts of modularity, abstraction, composition, and hierarchy are VERY important.