:orphan:

.. _send_data.py:

send_data.py
============

.. raw:: html

    <a target='new' href='../../ui/examples/send_data.html' style='font-size:small; float:right;'>open in new tab</a><div style='width: 500px; height: 300px; align: center; resize:both; overflow: hidden; box-shadow: 5px 5px 5px #777;'><iframe src='../../ui/examples/send_data.html' style='width: 100%; height: 100%; border: 2px solid #094;'>iframe not supported</iframe></div>

.. code-block:: py
    :linenos:


    """
    Example that demonstrates sending binray data from Python to JS. The
    ``Model.send_data()`` mechanism can be a powerful tool to send
    (scientific) data, especially for large amounts of data. The method
    accepts bytes or a URL ("http://" or "https://") where the
    data can be retrieved. At his point AJAX is used to retrieve the data.
    In the future we might push the data over a dedicated binary websocket
    for greater performance.
    
    If you find that you have a property that is a large list of numbers, maybe
    that should be considered data instead of a property. 
    
    Exported apps that use ``send_data()` work, but only if they are served
    (e.g. on a blog, readthedocs or S3), because browsers typically refuse
    to load local files via AJAX.
    """
    
    from flexx import ui, app
    from flexx.pyscript.stubs import window
    
    try:
        import numpy as np
    except ImportError:
        np = None
    
    
    N = 1000
    
    # Create array of N random float values. On numpy its easy
    if np:
        data = np.random.normal(0, 1, N)
    else:
        # fallback for when numpy is not avail
        import random
        import ctypes
        data = (ctypes.c_double * N)()
        for i in range(N):
            data[i] = random.random()
    
    
    class SendData(ui.Widget):
        """ A simple example demonstrating sending binary data from Python to JS.
        """
        
        def init(self):
            self.label = ui.Label()
            self.style = 'overflow-y: scroll'  # enable scrolling
            
            # Send data to the JS side. In this case we don't need meta data
            meta = {}
            bb = data.tobytes() if hasattr(data, 'tobytes') else bytes(data)
            self.send_data(bb, meta)
        
        class JS:
            
            def receive_data(self, blob, meta):
                # This is the method to implement to handle received binary data
                
                # The first argument is an (untyped) arraybuffer,
                # we know its float64 in this case.
                data = window.Float64Array(blob)
                
                # Show the data as text. We could also e.g. plot it.
                text = ['%i: %f<br />' % (i, data[i]) for i in range(len(data))]
                header = 'This data was send in binary form:<br />'
                self.label.text = header + ''.join(text)
    
    
    if __name__ == '__main__':
        m = app.launch(SendData)
        app.run()