Multiple namespaces for IPython¶

Feature request for @ProjectJupyter: Define multiple namespaces within the same notebook (without using functions).
— Juan Manuel Caicedo (@cavorite) May 5, 2016

This is a simple proof-of-concept implementation of switching namespaces via magics. The key points we need:

IPython's namespace is stored on the .user_ns attribute on the IPython instance
IPython relies on some globals in the user ns created with ip.init_user_ns
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]:

%ns foo

a = 5

%ns bar

a = 10

%ns foo

a

Out[3]:

In [4]:

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

Out[4]:

In [5]:

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

Out[5]:

In [6]:

%whos

Variable        Type        Data/Info
-------------------------------------
ChainMap        ABCMeta     <class 'collections.ChainMap'>
a               int         5
set_namespace   function    <function set_namespace at 0x109866d90>

In [7]:

%ns bar
%whos

Variable        Type        Data/Info
-------------------------------------
ChainMap        ABCMeta     <class 'collections.ChainMap'>
a               int         10
set_namespace   function    <function set_namespace at 0x109866d90>

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]:

%%ns cellns

a = 'hello,'
print(a * 2)

hello,hello,

This didn't affect the running namespace:

In [10]:

Out[10]:

But we can recall the cell namespace:

In [11]:

%%ns cellns
a

Out[11]:

'hello,'

In [12]:

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

foo 5
bar 10
default undefined
cellns hello,