defaultcontext
Tiny util for creating `tensorflow`_-like context managers for default instances of classes.
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 theinstancebecomes 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()) # NoneIf 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() # defaultAlternatively, 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
