Week4_Python

Python Training Part II:snake:

Topics Covered In This Course:

For part I Click Here

Part II

• HTTP Requests and Python APIs
• JSON API with Python
  • CRUD
• Python Decorators
• Test Driven Development (TDD)
• Error Handling
• File Handling
• Using databases with Python
  • Using Pandas library, joining data using DataFrames

Terminology

APIs

• Application Programming Iinterface (API)
• Set of tools that takes data and information and makes it universally accessible
• API makes a call to a server or database, executes request and returns response
• Gives programmers access to company's product or set of code that can be injected into your own project without having to build from scratch.
• Lately used to describe a kind of web interface.
• Web API is part of website designed to interact with programs that use specific URLs to request certain information (API call)
• Requested data returned in an easily processed format such as JSON or CSV.
• Built around HTTP protocol (meaning any programming language can be used to access them) e.g. Python, Java, Javascript, etc have at least one HTTP library to make this process easier.

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CRUD

• When building APIs, we want our models to provide four basic types of functionality.
• The model must be able to CREATE, READ, UPDATE, and DELETE resources.
• CRUD paradigm common in constructing web applications, because it provides a memorable framework for reminding developers of how to construct full, usable models.

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CSV

• Comma-separated values file
• Allows data to be saved in a tabular format

Using pandas library to import CSV file into Python

import pandas as pd

Using pyodbc to connect Python to SQL server

import pyodbc

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HTTP(Hypertext Transfer Protocol)

• Foundation of WWW, used to load web pages using hypertext links.
• HTTP is an application layer protocol designed to transfer information between networked devices and runs on top of other layers of the network protocol stack
• A typical flow over HTTP involves a client machines making a request to a server, which then sends a response message.

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JSON(Javascript Object Notation)

• Based on a subset of JavaScript language, it is a data storage language, similar to XML but adopts a 'dictionary' style syntax
• It is commonly used for transmitting data in web applications (e.g. sending data from server to the client, so it can be displayed on a web)

Example of JSON object

{
  "first_name" : "Bob",
  "last_name" : "Shark",
  "location" : "Ocean",
  "online" : true,
  "no_friends" : 987
}

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REST(Representational State Transfer)

• Architectural style that defines set of standards to be used for creating Web services.
• REST-compliant systems or RESTful systems are characterised by how they are stateless and separate the concerns of client and server.
• REST is based on four methods defined by the HTTP protocol: POST, GET, PUT, and DELETE. These correspond to the four traditional actions performed on data in a database (CRUD): CREATE, READ, UPDATE, and DELETE.

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__name__ == __main__:

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Try, Except, Else, Finally

• Exceptions in python are objects that represent errors.
• Exceptions can be raised in many ways e.g passing invalid arguments to functions ("string" + int) or performing illegal operations (12/0).
• By default, exceptions stop Python programs and print a traceback to the console with information about the exception.

try:
    """
    Code with exception you want to catch. 
    If exception raised (error occurs), control leaves this block and goes to except block
    """
except:
    """
    Executed only if an exception was raised in the try block. Code executed in this block is like normal code. 
    """
else:
    """
    Code executed only if no exceptions were raised in the try block
    """
finally:
    """
    This code ALWAYS executes after the other blocks, even if there was an uncaught exception or a return statement in one of the other blocks.
    """

Find exercise HERE

Using Python Decorators

class ToyClass:
    def instancemethod(self):
        return 'instance method called', self
    
    @classmethod
    def classmethod(cls):
        return 'class method called', cls
    @staticmethod
    def staticmethod():
        return 'static method called'