deedee
~~~~~~
Dependency inversion for python, the easy way
Nutshell
--------
Deedee provides an API which enables the developer to use late binding for
default values in function definition.
Example:
.. code-block:: python
import deedee
class Database:
def select(self, query):
print("select", query)
@deedee.resolve
def handler(param_a, param_b, database=deedee.context.database):
print(param_a, param_b) # param_a and param_b are unchanged
print(database) # this will print a database instance
database.select("select * from table order by id") # this call will be successful
def main():
# register the default value (which will be used when calling handler)
deedee.context.register("database", Database())
# call the handler, the 3rd parameter will be the previously registered value
handler("param_1", "param_2")
if __name__ == '__main__':
main()
In python the binding of the default value happens at the function
defintion, so it is not possible to set the default parameter later on, the
expression after the '=' sign gets evaluated at the function definition.
With `deedee` this changes, so you can specify a reference instead, and later on, specify the value for that reference.
When the function is called later on, the decorator `deedee.resolve` will
resolve the reference of the default value.
This can be used to implement dependency injection and dependency inversion
patterns without using any boilerplate classes or functions.
Features
--------
* Lazy evaluation of the default parameters
* Default value can be overriden by specifying it during the call (same behaviour as 'normal' default values)
* It can be traced which function references to a given default parameter (soon)
* It can be checked that all references can be resolved in the future, so it
can be ensured that there will be no error with resolving during function
calls
* Context objects can be implemented by the user (it is not required to use deedee.context)
* Annotations can be use freely, the library doesn't use or change them
* Nearly straightforward implementation, good test coverage
Name
----
According to urban dictionary, deedee is:
A person who is always there when you need them. A strong survivor who can make it through anything.
In deedee the values you are registering to a context behave like this – they are always there when you need them.
