Study Hall covering breakpoints and OO.

r17-study-hall-breakpoints-oo.md

Study Hall Topics

Resources / URLs / Endpoints

http://api.joelburton.com/recipes/brownies?color=red

URL: "resource" : "/recipes/brownies"

REST "resource" (subject)

• "brownies" : resource recipe
• "recipes" : resource of all my recipes

HTTP methods ("verbs") -> (verb)

GET /recipes => list of my resources of recipes

combo of verb+subject resource + method

different endpoint:

GET /recipes POST /recipes (creates a resource in recipes) PUT /recipes/brownies (update brownie resource)

safe:

• doesn't change anything
• only safe method => GET
• all else => unsafe

idempotent:

• doing it multiple times same as once
• GET / PUT / PATCH / DELETE

<form method="POST">
  <input name="book-title">
  <button>Search</button>
</form>
         => GET /books?book-title=the+bell+jar
         => POST /books

Relationships

• "is-a" : "joel is a human", "a human is a mammal"

• "has-a" : "an invoice has a client [eg i bill apple]"

• "has-many" : "my company has many open invoices"

company -> invoices <- client

• /joelco/invoices/500 { clientcode: "apple" }

• /joelco/clients/apple {name: ..., address: ....}

Sessions, Cookies, and db.session

db.session

entirely unrelated to browser sessions

• it just wraps a database transaction
• you have to .commit to keep work or .rollback to clean fouled transactions

Cookies

A way we can maintain "state" over HTTP: have browser remember & re-present

Session

An abstraction over using cookies directly — uses them under the hood

Browser stores one (or more) cookies that hold the session data

Flask handles sending/validating authenticity of sessions

A magic dictionary because, even though the session object you import is global, it is magically about this browser

Debugging

• breaking or reinforcing your mental model
• why and how to read error messages
• stacktrace/backtrace/traceback
• what debuggers can answer for us:
  • where am and how did I get here?
  • what was I called with?
  • why was I called with that?
  • what am I going to return?
  • what are my variables?
  • how would my program work differently if x was equal to 32?
  • watch code run!

Some commands I’ll show:

pip install ipdb   # a prettier/nicer pdb for python
export PYTHONBREAKPOINT=ipdb.set_trace
flask run --without-threads --no-reload

Object Orientation

Big ideas in OO:

• abstraction
• encapsulation
• polymorphism

Different areas:

• “data oo”
• “specialized subclass/machine”
  • we will briefly visit this while learning how to absolutely crush your siblings in hangman

Unit Testing in Python