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Dispatching-1.4.0
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مشاهده بیشترتوضیحات
A library for overloading python functions
| ویژگی | مقدار |
|---|---|
| سیستم عامل | - |
| نام فایل | Dispatching-1.4.0 |
| نام | Dispatching |
| نسخه کتابخانه | 1.4.0 |
| نگهدارنده | [] |
| ایمیل نگهدارنده | [] |
| نویسنده | Nathan West |
| ایمیل نویسنده | UNKNOWN |
| آدرس صفحه اصلی | https://github.com/Lucretiel/Dispatch |
| آدرس اینترنتی | https://pypi.org/project/Dispatching/ |
| مجوز | LGPLv3 |
Dispatching
===========
A python library for overloading functions on type and signature.
Overview
--------
Sure, ``*args`` and ``**kwargs`` are great. But sometimes you need more-
you need to have genuinely distinct behavior based on the types or
layout of your arguments. ``dispatching`` allows you to do just that. By
attaching type annotations to your functions, and decorating them with
``dispatch``, you can have a group of functions and automatically
determine the correct one to call. No more ``elif isinstance`` chains,
or ``len(args)``, or ``arg in kwargs``.
Usage
-----
To use dispatching, create a ``DispatchGroup`` object. This object
collects all the functions that should be tried when executing a
dispatch call.
.. code:: python
import dispatching
greetings = dispatching.DispatchGroup()
To add a function to the dispatch group, decorate it with the
``dispatch`` member.
.. code:: python
@greetings.dispatch
def greet(x: int):
print("Hello, int!")
@greetings.dispatch
def greet(x: str):
print("Hello, str!")
greet(1) # Prints "Hello, int!"
greet('string') # Prints "Hello, str!"
greet([1, 2, 3]) # Raises DispatchError, a subclass of TypeError
The argument annotation determines what function is called. Each
function registered to the group is tried, in order, to have arguments
bound to its parameter signature. The first one that matches is called.
If none match, a DispatchError is raised.
Not every argument needs to have an annotation. Use a completely
unannotated function to create a base case, which will be called if
nothing else matches:
.. code:: python
@greetings.dispatch
def greet(x):
print("Hello, mysterious stranger!")
greet([1, 2, 3]) # Prints "Hello, mysterious stranger!"
greet(1) # Still prints "Hello, int!"
Be careful, though. Functions are tried in the order that the are
decorated, so adding additional overloads after a base case won't do any
good:
.. code:: python
@greetings.dispatch
def greet(x: list):
print("Hello, list!")
greet([1, 2, 3]) # still prints "Hello, mysterious stranger"
To get around this, you can use the dispatch\_first decorator, which
adds the function to the front of the list of functions to try:
.. code:: python
@greetings.dispatch_first
def greet(x: list):
print("Hello, list!")
greet([1, 2, 3]) # now prints "Hello, list!"
Other usage notes
-----------------
It is not nessesary to explicitly create a DispatchGroup object.
Instead, you can use the global function ``dispatch`` to create a new
``DispatchGroup`` implicitly. The decorated functions will automatically
have the ``dispatch`` and ``dispatch_first`` attributes attached to
them, so that more overloads can be added.
.. code:: python
@dispatching.dispatch
def half(x: int):
return x / 2
@half.dispatch
def half(x: str):
return x[0:len(x)/2]
This applies when using an explicit ``DispatchGroup`` as well. Because
everything has the attributes attached to it, it also isn't necessary to
give all functions the same name, or to give them a different name than
the ``DispatchGroup``.
In addition to matching by type, you can match by number of arguments:
.. code:: python
@dispatching.dispatch
def nargs(a):
return 1
@nargs.dispatch
def nargs(a, b):
return 2
@nargs.dispatch
def nargs(a, b, c):
return 3
assert nargs(1) == 1
assert nargs(5, 4, 3) == 3
assert nargs(2, 4) == 2
#Using less than 1 or more than 3 will raise a DispatchError
Or by predicate:
.. code:: python
def is_odd(x): return x % 2 == 1
def is_even(x): return x % 2 == 0
@dispatching.dispatch
def evens_only(x: is_even):
return x
@evens_only.dispatch
def evens_only(x: is_odd)
raise ValueError(x)
Or by value comparison:
.. code:: python
#Classic freshman recursion
@dispatching.dispatch
def fib(n: 0):
return 1
@fib.dispatch
def fib(n: 1)
return 1
@fib.dispatch
def fib(n):
return fib(n-1) + fib(n-2)
Examples
--------
Overload on number of arguments to make automatic decorators:
.. code:: python
from dispatching import dispatch
#Non-decorator version
@dispatch
def add_return_value(func, additional):
def wrapper(*args, **kwargs):
return func(*args, **kwargs) + additional
return wrapper
#decorator version.
@add_return_value.dispatch
def add_return_value(additional):
def decorator(func):
return add_return_value(func, additional)
return decorator
plus_one_len = add_return_value(len, 1)
assert plus_one_len([1, 2, 3]) == 4
@add_return_value(10)
def double_add_10(x):
return x * 2
assert double_add_10(5) == 20
نحوه نصب
نصب پکیج whl Dispatching-1.4.0:
pip install Dispatching-1.4.0.whl
نصب پکیج tar.gz Dispatching-1.4.0:
pip install Dispatching-1.4.0.tar.gz