Python Master ClassPart 2

By Chathuranga Bandarawww.chathuranga.com

AgendaSome advanced concepts in Python

Exceptions Handling in Python

ORM - SQLAlchemy

Unit testing in Python

GeneratorsGenerators are a simple and powerful tool for creating iterators.

ie:

What is wrong there?The code is quite simple and straightforward, but its builds the full list in memory. This is clearly not acceptable in our case,

because we cannot afford to keep all n "10 megabyte" integers in memory.

Generator pattern may be?

Still Have issues.● Lots of code / boilerplate

● Hard to read

Generators to the Rescue!

Some Dark Magic there! WTF is yield?

Yield is a keyword that is used like return, except the function will return a generator.

When a yield statement is executed, the state of the generator is frozen and the value of expression_list is returned to next()‘s caller. By “frozen” we mean that all

local state is retained, including the current bindings of local variables, the instruction pointer, and the internal evaluation stack: enough information is saved so that the next time next() is invoked, the function can proceed exactly as if the

yield statement were just another external call.

Iterators It's a stateful helper object that will produce the next value when you call next() on

it. Any object that has a __next__() method is therefore an iterator. How it produces a value is irrelevant.

ie: inbuilt iterators

Custom Iterators

Decorators Some sh*t which is very useful

What is a decorator?decorators dynamically alter the functionality of a function, method or class without

having to directly use subclasses.

Some ContextWe can assign names to functions right?

Also Closures. (yes. JS stole it from here)

Also Higher Order Functions

Return a function

Finally Decorators! (stitch all the sh*t together)

Python Decorator Syntax

Better way?

Passing Arguments to decorators

More Pythonic

Exceptions Handling in PythonTry and Catch that nigga!

Syntax

How to raise an Exception

Custom Exceptions

ORM for Flask

pip install Flask-SQLAlchemy

Relationships?

Do Something!

Small Applications/yourapplication /yourapplication.py /static /style.css /templates layout.html index.html login.html ...

Packages/yourapplication /runserver.py /yourapplication /__init__.py /views.py /static /style.css /templates layout.html index.html login.html ...

With Blueprintsyourapp/

__init__.py

static/

templates/

home/

control_panel/

admin/

views/

__init__.py

home.py

control_panel.py

admin.py

models.py

Unit Testing

Inbuilt?

Nose helps you manage unit tests

pip install unittest2

Questions?

That’s all for today Folks!