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Structure python code with packages – import functions from different files

A modular application is an application composed of loosely coupled, functional units called modules, and these modules can be linked together to form a larger application. When you implement your python applications you should create such structures instead of big monoliths.

In this guide I will demonstrate how you can call python function from different folders and files (called packages). I have created a flask application which has as entrypoint the app.py file.

The solution is structured as shown below. The app folder is the root folder which contains all the code for the application. In the root hierarchy the app.py is placed along with other folders as templates, static and helpers.

As I need to create a helper function that will request data from an external API I created a file named github inside my helpers folder and I defined a function within it.

The function is very simple and returns a simple message. Code for github.py can be found below.

def my_function():
  return "Hello from function"

In order to call your helper functions from your main app or from another python package you should first import package

from helpers import github

and then use the function.

@app.route("/")
def home():
    return github.my_function()

This code will display on my flask main page the message of the function.

You can perform in such way any other activities by specifying your python file and then the function.

pythonFile.Function()
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##[error]Script failed with error: Error: Unable to locate executable file: ‘pwsh’.

In AzureCLI@2 you may choose from a variety of options when it comes on how this task will be executed on the agent machine. I usually choose powershell for windows machines and powershell core for Unix based machines (pwsh).

Recently I got an error on a Windows machine when using Powershell core. The latest version of powershell which is currently on 7.* version can be used as pscore in the AzureCLI@2 task.

      - task: AzureCLI@2
        displayName: az cli task
        inputs:
          azureSubscription: 'SERVICE-CONNECTION'
          scriptType: 'pscore'
          scriptLocation: 'inlineScript'
          inlineScript: |
           script

Error message:

##[error]Script failed with error: Error: Unable to locate executable file: ‘pwsh’. Please verify either the file path exists or the file can be found within a directory specified by the PATH environment variable. Also verify the file has a valid extension for an executable file.

Solution:

In order to bypass this problem you should make sure that the latest version of powershell which is multiplatform should be installed on your system. At the time of this article this version is 7.*

After installing powershell you should make a restart also on the machine in order for the environmental variables to be added on PATH. Then you can execute your pwsh tasks on your agent machines.

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Initialize and format windows disk with powershell

Sometimes you may need to automatically create windows disk for a virtual server using an automation mechanism. With the below powershell you can initialize a new emtpy disk with GPT partition and format it according to your needs.

You can get your available disks using:

Get-Disk

You can use the below powershell and change the below settings:

DriveLetter : What your drive letter will be
AllocationUnitSize: Default is 4k, but in my case I define 64k
DiskNumber: number of disk from Get-Disk command
NewFileSystemLabel: name of the volume

 Initialize-Disk -number 4 -partitionstyle GPT ; New-Partition -DiskNumber 4 -UseMaximumSize ; Format-Volume -DriveLetter G -FileSystem NTFS -AllocationUnitSize 65536 -NewFileSystemLabel Volume-Name

After applying the volume will be created and initialized.

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Install azure cli using Powershell – silent mode

Az cli is a very important tool that one devops engineer may need to install on systems. You can perform a silent install on a windows machine using the powershell below:

$msiFilePath = "azure-cli.msi"
Invoke-WebRequest https://aka.ms/installazurecliwindows -OutFile $msiFilePath
             
$MSIArguments = @(
    "/i"
    ('"{0}"' -f $msiFilePath)
    "/qn"
    "/norestart"
)               
Start-Process "msiexec.exe" -ArgumentList $MSIArguments -Wait -NoNewWindow
Remove-Item -Path $msiFilePath  -Force

By running the powershell the download procedure will begin.

When the installation finishes you can locate it under installed programs:

https://docs.microsoft.com/en-us/cli/azure/install-azure-cli-windows?tabs=azure-cli