24. May 2015

How to revert no-site-packages for virtualenv on Windows with Python 3.4

Python has support for virtual environment. It’s very handy to set up isolated space where you can store specific packages for the project. You can use command virtualenv to create virtual environment.

It’s very common to add option --no-site-packages which will isolate environment from packages installed in system.

Sometimes it is necessary to revert this option.

Linux and Mac users can control it by mechanism based on one file:

venv/lib/python3.4/no-global-site-packages.txt

When this file exists Python is ignoring packages from system.

In case of Windows there is configuration file stored in venv/pyenv.cfg and you can change configuration of global packages:

home = c:\Python34
include-system-site-packages = true
version = 3.4.3

Change the configuration and call Scripts\Activate.ps1 to load Python virtualenv to PowerShell.

Posted in Software engineering (Tags: , , ) | Comments Off on How to revert no-site-packages for virtualenv on Windows with Python 3.4

10. April 2014

PowerShell in Terminal of IntelliJ Idea

IntelliJ Idea has neat feature – Terminal Window.

Unfortunately on Windows it’s set just to old school cmd. Good news is that it’s possible to change it to something better. E.g. PowerShell.

Go to project settings, type “terminal”. Change value in Shell path to powershell.exe.

intellij-idea-powershell

Then you can invoke Terminal:

idea-terminal

Note: If you’re using 32bit version of Idea then it will open 32bit version of PowerShell. This is important when you want to change Set-ExecutionPolicy. 32bit and 64bit PowerShell have two different settings.

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29. June 2013

True/False gotcha Python vs Ruby vs PowerShell vs NodeJS vs PHP

Evaluation of conditions is very important part programming. True is ture, false is false…

Or not? It might surprise you, but not all languages evaluate numbers, empty strings or empty arrays in the same way.

Let’s examine several technologies. Python, Ruby, PowerShell, NodeJS and PHP.

Here is small code written in Python:

def test(value):
    if value:
        print "True"
    else:
        print "False"

test(0)
test(1)
test("")
test([])
test({})

Here is similar code written in Ruby:

def test(value)
    if value
        print "True"
    else
        print "False"
    end
end

test(0)
test(1)
test("")
test([])
test({})

Let’s compare it to PowerShell:

Function Test($value) {
    if ($value) {
        Write-Host "True"
    } else {
        Write-Host "False"
    }
}

Test(0)
Test(1)
Test("")
Test(@())
Test(@{})

Same logic in JavaScript for NodeJS:

function test(value) {
    if (value) {
        console.log("True");
    } else {
        console.log("False");
    }
}

test(0);
test(1);
test("");
test([]);
test({});

Code in PHP:

<?php 
function test($value) {
    if ($value) {
        echo "True";
    } else {
        echo "False";
    }
}

test(0);
test(1);
test("");
test(array());
test(array());
?>

Results are little bit surprising:

 

Python Ruby PowerShell NodeJS PHP
0 False True False  False False
1 True True True True True
“” False True False False False
[] False True True  True False
{} False True True  True False

Posted in Software engineering (Tags: , , , , , ) | Comments Off on True/False gotcha Python vs Ruby vs PowerShell vs NodeJS vs PHP

26. May 2013

How to activate Python virtual environment in PowerShell

It’s quite easy to set up virtual a environment with isolated packages for Python in PowerShell. There are several methods

Method 1. Pipenv

This is the youngest and most convenient method. Pipenv automatically manages the environment and can create virtualenv based on the working directory. Files with virtualenv are stored in a separate directory and the user does not need to worry about them.

Install pipenv package:

python3 -m pip install pipenv

Enter the directory where you’d like to work and type:

pipenv shell

Pipenv will bootstrap and activate the environment. It will launch subshell. If you’d like to leave the environment simply close the shell by command:

exit

Method 2. Using embedded venv

Python 3 contains package venv. It’s often confused with virtualenv which is a standalone package to manage virtual environments. The advantage of the command is that you do not need to install additional packages. Just create a virtual environment in the directory like pyenv:

python3 -m pyenv

Activate the environment:

.\pyenv\Scripts\activate.ps1

To deactivate the environment simply call:

deactivate

Method 3. Good old virtualenv

Creating a virtual environment with virtualenv is an old method. You need to create a directory that will contain the virtual environment and then activate it. virtualenv is not part of the default Python package, it’s necessary to install it:

python3 -m pip install virtualenv

Now it’s possible to create a new virtualenv in a directory like pyenv by the following command:

virtualenv pyenv

The last step is to activate this environment in PowerShell :

.\pyenv\Scripts\activate.ps1

You should see the name of your virtual environment in the command line. The virtual environment is active.

To deactivate the environment simply call:

deactivate

Posted in Software engineering (Tags: , , , ) | Comments Off on How to activate Python virtual environment in PowerShell

11. May 2013

Edge – invoke PowerShell from NodeJS

Project Edge allows seamless integration of NodeJS and PowrShell.

Just install packages:

npm install edge
npm install edge-ps

Create NodeJS application which contains PowerShell code:

var edge = require('edge');

var hello = edge.func('ps', function () {/*
"PowerShell welcomes $inputFromJS on $(Get-Date)"
*/});

hello('Node.js', function (error, result) {
 if (error) throw error;
 console.log(result[0]);
});

Start application and you’ll get output

PowerShell welcomes Node.js on 05/11/2013 07:14:38

Project Edge also allows integration of NodeJS with other technologies (e.g. Python)

Posted in Software engineering (Tags: , , , ) | 1 Comment

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