#!/usr/bin/env python
# coding: utf-8

# # Updatable Displays
# 
# Note: This feature requires notebook >= 5.0 or JupyterLab, and 
# 
# 
# IPython 6 implements a new API as part of the Jupyter Protocol version 5.1 for easily updating displays.
# 
# When you display something, you can now pass a `display_id` argument to attach an id to that output.
# 
# Any future display with the same ID will also update other displays that had the same ID.
# 
# `display` with a `display_id` will return a `DisplayHandle`
# object, which gives you easy access to update the output:

# In[10]:


from IPython.display import display, update_display


# In[13]:


handle = display('x', display_id='update-me')
handle


# When we call `handle.display('y')`, we get a new display of 'y',
# but in addition to that, we updated the previous display.

# In[14]:


handle.display('y')


# We can also *just* update the existing displays,
# without creating a new display:

# In[15]:


handle.update('z')


# You don't have to generate display_ids yourself,
# if you specify `display_id=True`, then a unique ID will be assigned:

# In[16]:


handle = display("hello", display_id=True)
handle


# Calling `handle.display(obj)` is the same as calling `display(obj, handle.display_id)`,
# so you don't need to use the handle objects if you don't want to:

# In[17]:


display('x', display_id='here');


# In[18]:


display('y', display_id='here');


# And just like `display`, there is now `update_display`,
# which is what `DisplayHandle.update` calls:

# In[19]:


update_display('z', display_id='here')


# ## More detailed example
# 
# One of the motivating use cases for this is simple progress bars.
# 
# Here is an example ProgressBar using these APIs:

# In[35]:


import os
from binascii import hexlify

class ProgressBar(object):
    def __init__(self, capacity):
        self.progress = 0
        self.capacity = capacity
        self.html_width = '60ex'
        self.text_width = 60
        self._display_id = hexlify(os.urandom(8)).decode('ascii')
        
    def __repr__(self):
        fraction = self.progress / self.capacity
        filled = '=' * int(fraction * self.text_width)
        rest = ' ' * (self.text_width - len(filled))
        return '[{}{}] {}/{}'.format(
            filled, rest,
            self.progress, self.capacity,
        )
    
    def _repr_html_(self):
        return """<progress
            value={progress}
            max={capacity}
            style="width: {width}"/>
            {progress} / {capacity}
        """.format(
            progress=self.progress,
            capacity=self.capacity,
            width=self.html_width,
        )
    
    def display(self):
        display(self, display_id=self._display_id)
    
    def update(self):
        update_display(self, display_id=self._display_id)

bar = ProgressBar(10)
bar.display()


# And the ProgressBar has `.display` and `.update` methods:

# In[36]:


import time

bar.display()

for i in range(11):
    bar.progress = i
    bar.update()
    time.sleep(0.25)


# We would encourage any updatable-display objects that track their own display_ids to follow-suit with `.display()` and `.update()` or `.update_display()` methods.