Installation

You can install defaultcontext using pip:

pip install defaultcontext

Usage

The library provides the with_default_context class decorator which simply does two things:

• Adds static method Class.get_default() which returns the default object in the current context block.

• Adds method instance.as_default() to the class, which manages a context within which the instance becomes default

This is useful for creating psuedo-global objects that can be accessed from any code executed within a given context block without passing such objects around.

This idea is inspired by Graph and Session classes from Google’s tensorflow.

Basic usage:

from defaultcontext import with_default_context


@with_default_context
class Environment:
    def __init__(self, name):
        self.name = name

    def __str__(self):
        return 'Environment %s' % self.name


with Environment(name='A').as_default():
    print(Environment.get_default())      # A

with Environment(name='B').as_default():
    print(Environment.get_default())      # B

print(Environment.get_default())          # None

If with_default_context was called without parameters the global default value of a class will be None. The global default can be added using global_default_factory:

def make_default_env():
    return Environment(name='default')

@with_default_context(global_default_factory=make_default_env)
class Environment:
    def __init__(self, name):
        self.name = name

    def __str__(self):
        return self.name

Environment.get_default()                      # default

with Environment(name='custom').as_default():
    print(Environment.get_default())           # custom

Environment.get_default()                      # default

Alternatively, if the class can be constructed without arguments, global default can be set to Class() by setting use_empty_init to True:

@with_default_context(use_empty_init=True)
class Environment:
    def __init__(self, name='default'):
        self.name = name

    def __str__(self):
        return self.name

Environment.get_default()                      # default

with Environment(name='custom').as_default():
    print(Environment.get_default())           # custom

Environment.get_default()                      # default