list(map(lambda x:x[0]+x[1], zip(a,b)))


Concise vector adding in Python?
I'm very new to xaml and I'm trying to understand the Binding issue. I have a problem with the Array Binding. I created this very simple example: I have a stack panel with three images. Each image has a RotationTransform. Each Angle is obtained by an array element (the array is a DependencyProperty called Rotations). This is the xaml simple file:

&lt;StackPanel Orientation="Vertical"&gt;
        &lt;Image Source="/Assets/knife.png" Width="50" Height="100" Stretch="Uniform" RenderTransformOrigin="0.5,0.5"&gt;
            &lt;Image.RenderTransform&gt;
                &lt;RotateTransform Angle="{Binding ElementName=pageRoot, Path=Rotations[0], Mode=OneWay}"/&gt;
            &lt;/Image.RenderTransform&gt;
        &lt;/Image&gt;

        &lt;Image Source="/Assets/fork.png" Width="50" Height="100" Stretch="Uniform" RenderTransformOrigin="0.5,0.5"&gt;
        &lt;Image.RenderTransform&gt;
            &lt;RotateTransform Angle="{Binding ElementName=pageRoot, Path=Rotations[1], Mode=OneWay}"/&gt;
        &lt;/Image.RenderTransform&gt;
        &lt;/Image&gt;

        &lt;Image Source="/Assets/spoon.png" Width="50" Height="100" Stretch="Uniform" RenderTransformOrigin="0.5,0.5"&gt;
            &lt;Image.RenderTransform&gt;
                &lt;RotateTransform Angle="{Binding ElementName=pageRoot, Path=Rotations[2], Mode=OneWay}"/&gt;
            &lt;/Image.RenderTransform&gt;
        &lt;/Image&gt;

        &lt;Button x:Name="actionButton" Content="Try Binding!" 
                Click="Op_Click"/&gt;            
    &lt;/StackPanel&gt;


And this is my c# class:

public sealed partial class MainPage : Page
    {        
        public static readonly DependencyProperty RotationsProperty = DependencyProperty.Register("Rotations", typeof(double[]), typeof(MainPage),
            new PropertyMetadata(new double[3]));

        public double[] Rotations
        {
            get { return (double[])GetValue(RotationsProperty); }
            set { SetValue(RotationsProperty, value); }
        }

        private void Op_Click(object sender, RoutedEventArgs e)
        {
            Rotations[0] = 180;
            Rotations[1] = 130;
            Rotations[2] = 350;
        }

        public MainPage()
        {
            this.InitializeComponent();
            Rotations[0] = 20;
            Rotations[1] = 90;
            Rotations[2] = 180;
        }
    }


The binding works only the first time (at startup time). When I click on the button (changing the Rotations array) the binding doesn't work and it is completely ignored from my images. 

This is a very simple example, so it's clear that I miss something concerning the Binding issue.
