diana 0.0.4

Simple Dependency Injector for python

A simple dependency injection framework for python.

Simple Example

from diana import injector


def my_factory():
    return "FactoryValue"

FactoryValue = object()
injector.provide(FactoryValue, factory=my_factory)

OtherValue = object()
injector.provide(OtherValue, value="OtherValue")

# Hard injection, provider must exist
@injector(fish=FactoryValue, cat=OtherValue)
def foo(fish=None, cat=None):
    return (fish, cat)

# Soft injection, missing dependencies will be filled with `None`
@injector.soft(horse=MissingValue)
def bar(horse):
    return horse

foo()  # Returns `('FactoryValue', 'OtherValue')`
bar()  # Returns `None`

You can also decorate factories:

from diana import injector

FactoryValue = object()

@injector.factory(FactoryValue)
def my_factory():
    return "FactoryValue"

Aliases

You might not want to have to handle importing of ‘loose’ objects. Diana supports aliases for provided dependencies.

from diana import injector
FactoryValue = object()

@injector.factory(FactoryValue, aliases=('FactoryValue', 'trout'))
def my_factory():
    return "FactoryValue"

@injector(fish='trout')
def foo(fish):
    return fish

foo()  # Returns "FactoryValue"

Contextual Overrides

In some situations, you may not want to use the default value for a given dependency (e.g. testing). You can override the default temporarily like so:

from diana import injector
FactoryValue = object()

@injector.factory(FactoryValue)
def my_factory():
    return "FactoryValue"

@injector(fish='trout')
def foo(fish):
    return fish

with injector.override(FactoryValue, factory=lambda: "Other"):
    foo()  # Returns "Other"

foo()  # Returns "FactoryValue"

Caution!

Contextual overrides are not thread safe.

Scopes

The lifecycle of provided dependencies can be managed with scopes. A few scopes are shipped with Diana by default.

from diana import injector, Const
FactoryValue = object()

@injector.factory(FactoryValue, scope=Const)
def my_factory():
    time.sleep()
    return "FactoryValue"

@injector(fish=FactoryValue)
def foo(fish):
    return fish

foo()
foo()  # `my_factory` is not called a second time.