shield

Sometimes you need to instantiate classes that were not designed to be used in dependency injection context. For example, it has variable length positional or keyword arguments. Commonly known as *args and **kwargs. Our dependency injection implementation highly coupled with constructor signature of the class. We have to know ahead what arguments we need to pass to the class by names.

For specific cases like this we introduced shield object. It allows you to specify necessary signature manually. In that case dependency injection engine would know what arguments to pass.

Principles

• Variable-length positional arguments could be specified

Variable-length positional arguments could be specified

If you specify positional arguments next to the class you want to build inside shield object signature, they would be injected based on on the semantic commonly used for such dependency type.

For example, scalar types would be passed as is. The same way they would be passed from Injector attributes.

>>> from dependencies import Injector, shield

>>> class Sum:
...     def __init__(self, *args):
...         self.args = args
...
...     def do(self):
...         return sum(self.args)

>>> class Wrong(Injector):
...     sum = Sum

>>> Wrong.sum.do()
Traceback (most recent call last):
  ...
_dependencies.exceptions.DependencyError: 'Sum.__init__' have variable-length positional arguments

>>> class Container(Injector):
...     sum = shield(Sum, 1, 2)

>>> Container.sum.do()
3

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