Coding Principles

Principles

• Loose Coupling
• High Cohesion
• Change is Local
• It is Easy to Remove

Smells

• Rigidity ( A -> B -> C . something hardcoded in C )
• Fragility
• Immobility
• Viscosity of Design (Taking a shortcut and introducing technical debt requires less effort than doing it right.)
• Viscosity of Environment (skipping rigorous testing)
• Needless Complexity
• Needless Repetition
• Opacity

Class Design

• Single Responsibility Principle (SRP)
• Open Closed Principle (OCP)
• Liskov Substitution Principle (LSP)
• Dependency Inversion Principle (DIP)
• Interface Segregation Principle (ISP)
• Classes Should be Small

General

• Follow Standard Conventions
• Keep It Simple Stupid
• Boy Scout Rule
• Avoid Multiple Languages in One Source File

Design

• Keep Configurable Data at High Levels
• Don’t Be Arbitrary (Have a reason for the way you structure your code)
• Be Precise

Dependencies

• Make Logical Dependencies Physical
• Singletons / Service Locator
• Base Classes Depending On Their Derivatives

Naming

• Choose Descriptive / Unambiguous Names (Names have to reflect the entire functionality)
• Standard Nomenclature Where Possible
• no Encodings in Names (No prefixes, no type/scope information)

Understandability

• maintain Consistency
• Use Explanatory Variables
• Prefer Dedicated Value Objects to Primitive Types (path type , instead of String , enclosing class)
• Poorly Written Comment
• Obscured Intent (Too dense algorithms that lose all expressiveness.)
• Obvious Behaviour Is Unimplemented
• Hidden Logical Dependency

Methods

• Methods Should Do One Thing
• Methods Should perform what is described by the name of the function.
• Avoid Method with Too Many Input Arguments
• Avoid Method with Too Many output Arguments (return object instead)
• Avoid Selector / Flag Arguments
• Avoid Inappropriate Static

Source Code Structure

• Variables and methods should be defined close to where they are used.
• Local variables should be declared just above their first usage ,depending on scope
• Nesting (should be more specific)
• Structure Code into Namespaces by Feature
• same feature together. Eg :A feature may use another feature; a business feature may use a core feature like logging

Useless Stuff

• Avoid Dead Comment, Code
• Avoid Clutter
• Inappropriate Information

Maintainability Killers

• Avoid Duplication
• Magic Numbers / Strings (Replace Magic Numbers and Strings with named constants)

Exception Handling

• Catch Specific Exceptions
• Catch Where You Can React in a Meaningful Way
• Use Exceptions instead of Return Codes or null
• Fail Fast
• Avoid Using Exceptions for Control Flow
• Avoid Swallowing Exceptions

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Azure Django-postgres Application

postgres-Django

Ref:Tutorial

Azure App Service

Creat APP

    git clone https://github.com/Azure-Samples/djangoapp
    cd djangoapp
    az webapp up \
    --resource-group DjangoPostgres-tutorial-rg \
    --location centralus \
    --plan DjangoPostgres-tutorial-plan \
    --sku F1 \
    --name djangopostgresapp

Add extension to db extension to CLI

    az extension add --name db-up   #install db-up (ref- https://gist.github.com/j-thepac/b0ab1196585cf8b9a8478e4a3c8b6aae)

Create a new Postgres instance

    az postgres up \
    --resource-group DjangoPostgres \
    --location centralus \
    --sku-name B_Gen5_1 \
    --server-name djangopostgresserver \
    --database-name pollsdb \
    --admin-user sqlusr \
    --admin-password Azure@123 \
    --ssl-enforcement Enabled

Note down DB details from console

Connect App and DB

    az webapp config appsettings set \
    --name djangopostgresapp \
    --settings DBHOST="djangopostgresserver" DBUSER="sqlusr" DBPASS="Azure@123" DBNAME="pollsdb" 

DB Migration

    az webapp ssh #open ssh 
    python manage.py migrate
    python manage.py createsuperuser # usn=root/password Pollsdb1
    #skip email 
    exit

Test :

    az webapp browse

open https://djangopostgresapp.azurewebsites.net/ (http://.azurewebsites.net/admin)

Update python file and redeploy

    Make any changes to python file
    az webapp up
    az webapp log tail

group delete

    az group delete --name DjangoPostgres --no-wait
    az group delete --name DjangoPostgres-tutorial-rg --no-wait

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 Azure Errors and Solution

az extension add --name db-up --debug

Error:

Building wheel for pymssql (PEP 517): finished with status 'error'
  ERROR: Failed building wheel for pymssql
Failed to build pymssql
ERROR: Could not build wheels for pymssql which use PEP 517 and cannot be installed directly
Exception information:

pip._internal.exceptions.InstallationError: Could not build wheels for pymssql which use PEP 517 and cannot be installed directly

Environnment :

• Mac Monetary
• Python 3.6

Ref

Stackoverflow Github

Solution

brew install freetds openssl
export LDFLAGS="-L/usr/local/opt/freetds/lib -L/usr/local/opt/openssl@3/lib"
export CFLAGS="-I/usr/local/opt/freetds/include"
export CPPFLAGS="-I/usr/local/opt/openssl@3/include"
az extension add --name db-up --debug

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Azure Linux VM

Azure Linux VM Connection

pre-Req: 

1. For Mac Users
2. Make sure linux machine is created

Steps:

1. Open Linux Machine Panel
2. Go to Settings > Connect > SSH
3. Click on other Clients
4. From the new page opened , Copy Create an SSH key Pair "ssh-keygen -m PEM -t rsa -b 4096"
5. Run "ssh-keygen -m PEM -t rsa -b 4096" in Terminal
6. Click Enter all the times

Testing Connection

1. In the previous page , enter the path of the id_rsa.pub Eg : "~/.ssh/id_rsa.pub" or "(if u have added the file in a new folder ) ~/.ssh/vm_linux/pushpa/id_rsa.pub " 
2. click on "test your connection"
3. Your unsaved edits will be discarded , ck Yes
4. Ck on Test Connection 
5. this shd pass

Connection:

1. Settings > Connect > SSH 
2. copy the run example ie ., ssh -i <private key path> pushpaxxxxx@1xx.xx.1xx.xx
3. Replace the privae key path to ids_rsa which was created
4. Make sure u give the azure account password when asked

Install Python3

1. sudo su
2. <azure password>
3. yum install python3
4. pip3 install requests

 Azure Static WebPage

Azure Static page:

Azure App Service

git clone https://github.com/Azure-Samples/html-docs-hello-world.git
cd html-docs-hello-world
az webapp up --location westeurope --name <app_name> --html
go to the app URL: http://<app_name>.azurewebsites.net

Update and redeploy the app

az webapp up --location westeurope --name <app_name> --html

Clean up

az group delete --name appsvc_rg_Windows_westeurope

Reference

https://docs.microsoft.com/en-us/azure/app-service/quickstart-html

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Azure API

Create Webapp using Flask

Azure App Service

Pre-Req

• Make Sure u have setup account created for Azure
• You have enabled Free Subscription
• You have created a webapp instance manullay example "flaskserverpushparanimptest2"

Setup Env

$brew update && brew install azure-cli
$az upgrade
$az version
$az login

Code Flask Api

$git clone https://github.com/Azure-Samples/python-docs-hello-world
$cd python-docs-hello-world
$python3 -m venv .venv
$source .venv/bin/activate
$pip install -r requirements.txt
$flask run

Test locally

test localy in browser : http://localhost:5000/ ctrl+C to Quit

Deploy to Azure

$az webapp up --sku F1 --name flaskserverpushparanimptest2 #sku is pricing F1 is free

Test Azure Web

open http://flaskserverpushparanimptest2.azurewebsites.net

Add new enhancement for your file and run below code

    $az webapp up

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 Azure Cosmos DB 

	"""
	https://docs.microsoft.com/en-us/azure/cosmos-db/sql/create-sql-api-python
	https://github.com/Azure/azure-sdk-for-python/blob/main/sdk/cosmos/azure-cosmos/samples/examples.py
	Pre-Req:
	pip install --pre azure-cosmos
	Have a Azure Account with Free Subscribption Enabled
	Make sure Cosmosa DB is created along with DB and Container
	#Azure portal > Azure Cosmos > ck on Existing Cosmos Db > Settings > Keys
	to get Primary key and endpoint
	"""
	from azure.cosmos import exceptions, CosmosClient, PartitionKey
	import uuid
	import json
	endpoint = "GET KEYS FROM : Azure portal > Azure Cosmos > ck on Existing Cosmos Db > Settings > Keys"
	key = 'GET KEYS FROM : Azure portal > Azure Cosmos > ck on Existing Cosmos Db > Settings > Keys'
	jsondata= {"id": "3","category": "hobby","name": "TV","description": "Pick up TV"}
	dbname="ToDoDatabase"
	containerid="ToDoList"
	query="SELECT * FROM ITEMS"
	class CosmosDb():
	def __init__(self,endpoint,key,dbname,containerid):
	self.endpoint=endpoint
	self.key=key
	self.client = CosmosClient(endpoint, key)
	self.database = self.client.get_database_client(database=dbname) #create_database_if_not_exists
	self.container = self.database.get_container_client(containerid) #create_container_if_not_exists
	def create_item(self,jsondata):
	self.container.create_item(body=jsondata)
	def list_containers(self,database_name):
	database = self.client.get_database_client(database_name)
	return database.list_containers()
	def modify_item(self,item_name,partition,key,new_value):
	item = self.container.read_item(item_name, partition_key=partition)
	item[key] = new_value
	updated_item = container.upsert_item(item)
	def query_items(self,query:str):
	return self.container.query_items(query=query,enable_cross_partition_query=True)
	cosmos=CosmosDb(endpoint,key,dbname,containerid)
	# res=cosmos.list_containers(dbname)
	res=cosmos.query_items("SELECT * FROM ITEMS")
	for i in res : print(json.dumps(i,indent=True))

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