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

# # Multiple namespaces for IPython
# 
# <blockquote class="twitter-tweet" data-partner="tweetdeck"><p lang="en" dir="ltr">Feature request for <a href="https://twitter.com/ProjectJupyter">@ProjectJupyter</a>: Define multiple namespaces within the same notebook (without using functions).</p>&mdash; Juan Manuel Caicedo (@cavorite) <a href="https://twitter.com/cavorite/status/728354406723297281">May 5, 2016</a></blockquote>
# <script async src="//platform.twitter.com/widgets.js" charset="utf-8"></script>
# 
# This is a simple proof-of-concept implementation of switching namespaces via magics. The key points we need:
# 
# 1. IPython's namespace is stored on the `.user_ns` attribute on the IPython instance
# 2. IPython relies on some globals in the user ns created with `ip.init_user_ns`
# 3. A namespace in Python is a dict
# 
# 

# First, we create a dict of namespaces by name on IPython, and save the initial value:

# In[1]:


ip = get_ipython()
ip.namespaces = {}
ip._original_user_ns = ip.user_ns


# Next, we define a `%ns` line magic for switching namespaces by name:
# 
# We use ChainMap so that globals that IPython defines, such as In, Out, etc. are available no matter what namespace we switch to:

# In[2]:


from collections import ChainMap

def set_namespace(name):
    """Line magic for switching namespaces:
    
    %ns foo
    a = 5

    %ns bar
    a = 10

    %ns foo
    print(a)
    # 10
    """
    if name not in ip.namespaces:
        ip.namespaces[name] = ChainMap({}, ip._original_user_ns)
    ip.user_ns = ip.namespaces[name]

ip.register_magic_function(set_namespace, magic_name='ns')
set_namespace('default')


# In[3]:


get_ipython().run_line_magic('ns', 'foo')

a = 5

get_ipython().run_line_magic('ns', 'bar')

a = 10

get_ipython().run_line_magic('ns', 'foo')

a


# In[4]:


ip.namespaces['foo']['a']


# In[5]:


ip.namespaces['bar']['a']


# In[6]:


get_ipython().run_line_magic('whos', '')


# In[7]:


get_ipython().run_line_magic('ns', 'bar')
get_ipython().run_line_magic('whos', '')


# We can also make a cell magic for running a whole cell in a given namespace,
# then switching back to whatever was already active:

# In[8]:


def namespace_cell(name, cell):
    """Cell magic for running a single cell in a given namespace
    
    %%ns foo
    a = 5
    """
    save_ns = ip.user_ns
    set_namespace(name)
    try:
        ip.run_cell(cell)
    finally:
        ip.user_ns = save_ns
    
    
ip.register_magic_function(namespace_cell, magic_kind='cell', magic_name='ns')


# In[9]:


get_ipython().run_cell_magic('ns', 'cellns', "\na = 'hello,'\nprint(a * 2)\n")


# This didn't affect the running namespace:

# In[10]:


a


# But we can recall the cell namespace:

# In[11]:


get_ipython().run_cell_magic('ns', 'cellns', 'a\n')


# In[12]:


for name, ns in ip.namespaces.items():
    print(name, ns.get('a', 'undefined'))