Built-in __repr__ and Internal Functions

__repr__ not __str__

This past week, we learned about a built-in function which was, to me, entirely new. It was presented to us in class under the heading "prefer repr to str" as follows:

repr is supposed to provide explicit information about an object and is returned when the class object itself is meant to be returned and str is what you want returned when print() is called on it. However, as we learned in lecture, repr acts as the substitute for str when no str method is defined for that class. So, classes should always have a repr method, whereas str is optional.

Internal functions

We also learned about defining functions under other function headers. At first this seemed like an entirely useless technique especially when the instructor mentioned that it is very hard to access the internal function individually from elsewhere. But, I made sure to clear up my conclusion and the answer I received was that a function with a generic name doing almost identical tasks might be required in many different functions in a file. This way, these internal functions can share a name yet have a slightly different implementation, which could be a very useful tool for programmers coding complicated classes.

The Thing About Recursion

Recursive data structures

Over the past few lectures, we've learned about different types of recursive data structures, mainly trees and linked lists. Trees are essentially linked lists in which each list has two or more sub-lists.

Leap of faith

Something that has been concerning me a bit has been the language used when the online textbook suggests implementing a method which involves recursion. It refers to assuming that the recursive call works is taking a leap of faith. As long as there is a base case for how to actually act on the data when the data is there to be acted upon, there should be no leap of faith involved.

The fear of recursion

That being said, it does always feel like recursion is something strange and unusual which seems to miraculously work. However, the feeling, when carefully examined is due to an unfounded fear. The fear is simply that the function you are calling is not complete. When you type the call into the function, sure, that is the case. But by the time you call the function, it is supposedly finished. The call is simply returning to the beginning of the function and passing a new value. Recursive data structures are very useful and not too hard to wrap your head around. It just takes some getting used to.

Object-Oriented Programming and Recursion

Object-Oriented Programming

Object-oriented programming (OOP) languages focus on creating objects (or classes) that contain data. Each object has methods associated with it that perform tasks specific to the data structure being used. Before the advent of OOP, programming languages focused on allowing the user to write procedures that operated on data. OOP is useful because specific data structures often have very specific ways in which data can be operated upon, and the methods defined for any object will reflect this. Methods that are apprpriate across multiple classes can be inherited to save a programmer from code duplication. OOP also allows programs to correspond more closely to objects in the real world. It seems that object-oriented programming is a very useful tool for computer programmers.

Recursion

Recursion is defined as defining something in terms of itself. In programming, recursion is referred to as a function that calls itself inside of itself. It is often used to analyze data that is organized recursively, such as data structures that have miniature versions of the same data structure contained within. For many problems in programming, recursion is the easiest and sometimes the only way to solve them. Otherwise, one would have to access each substructure in a new way. Recursive programs must also include some kind of exit condition, or the result may be an infinitely looping function call. Recursive programming mimics many structures in nature, such as trees, where each branch can be conceived of as a smaller tree.