Metadata-Version: 1.1
Name: Dispatching
Version: 1.0.1
Summary: A library for overloading python functions
Home-page: https://github.com/Lucretiel/Dispatch
Author: Nathan West
Author-email: UNKNOWN
License: LGPLv3
Description: 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.
        
        ```python
        import dispatching
        greetings = dispatching.DispatchGroup()
        ```
        
        To add a function to the dispatch group, decorate it with the `dispatch` member.
        
        ```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:
        
        ```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:
        
        ```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:
        
        ```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.
        
        ```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:
        
        ```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:
        
        ```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:
        
        ```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:
        
        ```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
        ```
        
Platform: any
Classifier: Development Status :: 4 - Beta
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: GNU Lesser General Public License v3 (LGPLv3)
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.3
Classifier: Topic :: Software Development
Classifier: Topic :: Software Development :: Libraries
Classifier: Topic :: Software Development :: Libraries :: Python Modules
