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

You can test code on-line in Cloud9 IDE except PowerShell example 😉

20. August 2012

Problems with deploying Heroku Django app from Windows

Deploying Django app to Heroku from Windows machine is little bit tricky.

You can follow instructions in Heroku manual. The first problem that you may encounter is with Postgres support in Python. There is problem with this command:

pip install Django psycopg2 dj-database-url

If you do not have Visual Studio installed on your machine, you’ll receive error that vcvarsall.bat is missing.

Solution is quite easy. You don’t need to install Visaul Studio. Just download binary version of psycopg2 module from http://www.stickpeople.com/projects/python/win-psycopg/

Then you can exclude psycopg2 from pip install command, because it is installed in system directory of Python.

Another tricky issue is with command:

pip freeze >requirements.txt

If you type this command in PowerShell then it will automatically create Unicode file with extra bytes. When you try to deploy project with messed requirements.txt to Herou then you’ll see self explanatory error 😉

TypeError: must be encoded string without NULL bytes, not str

Nice 🙂

Just open requirements.txt file with notepad and select Save as. In Save as dialog choose ANSI.

Commit file and push project to Heroku. It will work 😉

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