Kismet Arts Tangent

 

Joe Parente and Joey Perrott are doing afternoon sessions with the Web Coding Bootcamp. I’m learning a lot and transcribing my notes down below.

In our first python project, we’re working on a quote database using The Python NDB Datastore API.

Methods

As started the day before, the afternoon session continued on with fleshing out the methods associated with the QuoteModel class in our database. The first step was to list all of the behaviors and then write the methods.

In this project, we used both Class and Instance methods.

The instructors emphasized how simple methods are. You describe what they take, what they do, and what they return. In class, we split up into groups to write different methods that will be used in the data base.

Delete Method

I was in the delete group. We broke down the method into parts. Select the quote, confirm delete, put quote in the trash box, and hide quote on display. And we were wrong. The instructors told us to think like a computer. We’re deep into the back-end of the process. We’re at the point of actually deleting something.

The process of deleting a thing in a database. You get the id. In this method, we start out with the id, then find the entity it’s attached to, then delete the key. Apparently, if you delete a key to an entity, you essentially delete the entity.¹

In the making of a method, developers ask themselves, now, how would I break this. In this case, it would be to give a nonexisting ID number. So, we must validate that the id exists in the database. A simple “if not” (I like python, so clean.) will do the trick.

At first we raised a generic exception, but we were advised to make a custom exception, that way when we’re debugging, it will point to the exact problem and we will be better able to handle it. To make a custom exception, create a new class outside of the class (put it with the rest of your exception classes, you’ll probably have a few) and then call it in the method (as seen below).

 

Kwargs

In the following method, one of the parameters it takes in is **kwargs. It’s kind of a way of saying “stuff.” The important part is the asterisks and by convention, should name it kwargs, but you can name it anything. It just means that it can handle what you throw in.

“You would use *args when you’re not sure how many arguments might be passed to your function, i.e. it allows you pass an arbitrary number of arguments to your function.” — and kwargs are named arguments.

Source: python – *args and **kwargs? – Stack Overflow

 

Doc Strings

One can tell that one of the instructors wrote this code. There’s really excellent code comments. Each code comment states what the method does, what it takes in and what it returns. As for knowing what expressions to use, that could be found in the NDB Datastore API. Finding what you need takes some time and knowledge about how databases work.

Upvoting Method

This group’s challenge was to make sure that a person could only upvote a thing once and to remove the vote if the method was called again by the same user (a functionality similar to the “like button” on Facebook). Their solution was to require the username of the user to run the method and then storing that in the list and if that person’s name is already in the list they are taken out of the list.

Footnotes

1. My question for the instructor: What do keys, IDs and entities look like in a hierarchical diagram explaining the structure of a database?
   Answer: “There is no hierarchy. In a non-relational database everything is flat. Each object has one key that you can use to identify the object or you can query the object by one of its attributes.” -Joe

Joe Parente and Joey Perrott are doing afternoon sessions with the Web Coding Bootcamp. I’m learning a lot and transcribing my notes down below.

Python is an interpreted¹ programming language. It supports multiple programming paradigms, but the instructors mostly focused on the object oriented (OO) style. Everything can be understood as an object. Functions (methods²) and classes define actions and attributes for objects. There are statements (if, for, while, try, etc.) and expressions. Included data types are integers, strings, dictionaries, lists and my favorite tuple³ (mostly because it sounds cute).

I’m approaching this subject after becoming somewhat familiar with javascript so a lot of my learning is a bit of a translation from one programming language to another. Some things are the same like “append” but “prompt” becomes “raw input.” The list of Python reserved words and builtins will be good to memorize. The slicing is a little different from JavaScript Array slice() Method syntatically.

Class

There was a lot to be learned about classes. Classes have attributes and methods. Def__init__ defines the construction.

“The __init__ method (init for initialise) is called when the object is instantiated. Instantiation is done by (effectively) calling the class.”

Source: Introduction to OOP with Python

Handling Exceptions is the way Python doesn’t break when expected disconnects occur. Using a try block you can catch an error and have the program do something else.

Python works in and with other frameworks and languages:

• The Web framework for perfectionists with deadlines | Django
• LAMP (software bundle)
• App Engine — Google Cloud Platform
• Amazon Web Services (AWS) – Cloud Computing Services
• Interactive Wireframe Software & Mockup Tool | Axure (They mentioned this and I’m curious to see how we could use that.)

Databases

There are two types of databases, relational and non-relational⁴. In our first python project, we’ll be working on a quote database using The Python NDB Datastore API.

First, as a class, we created a model (a well defined data structure) with just attributes. Then, we translated that into a syntactically correct model that used Property Classes such as StringProperty.

Best Practices

• Name variables well (i.e. def Add (firstnumber, secondnumber).
• When programming, think of user experience along the way (in their example, they used “enumerate” to make the selection from the list easier.
• Except as narrow of an error as possible in try blocks.
• Never store a user’s password in a database in plain text.
• Do not expose your data base to the public.
• Always document your code (code comments called doc strings). When you comment on methods: say what it does, and talk about the required arguments and what they look like and what it returns.

Footnotes

1. Compiling vs. interpreting is mostly a matter of how the work of “understanding” the program is divided up between different processes, and the line is a bit blurry these days as languages and products try to offer the best of both worlds.

Source: java – Compiled vs. Interpreted Languages – Stack Overflow

2. Methods are associated with a class or instance, and “standalone functions” are not.

Source: python – Difference between methods and functions – Stack Overflow

3. The point of a tuple is that the i-th slot means something specific. In other words, it’s a index-based (rather than name based) datastructure.

Source: James Tauber : Python Tuples are Not Just Constant Lists

4. Therefore, in my opinion, the main difference is about how do you store the data and the storage level of the relationships between them.

Source: What is the difference between a Relational and Non-Relational Database? – Stack Overflow