Separate chain_of_responsibility script per python version

Author: gyermolenko

README.md

@@ -37,7 +37,7 @@ __Behavioral Patterns__:
 
 | Pattern | Description |
 |:-------:| ----------- |
-| [chain_of_responsibility](patterns/behavioral/chain_of_responsibility.py) | apply a chain of successive handlers to try and process the data |
+| [chain_of_responsibility](patterns/behavioral/chain_of_responsibility__py3.py) | apply a chain of successive handlers to try and process the data |
 | [catalog](patterns/behavioral/catalog.py) | general methods will call different specialized methods based on construction parameter |
 | [chaining_method](patterns/behavioral/chaining_method.py) | continue callback next object method |
 | [command](patterns/behavioral/command.py) | bundle a command and arguments to call later |

patterns/behavioral/chain_of_responsibility.py renamed to patterns/behavioral/chain_of_responsibility__py2.py

@@ -92,29 +92,28 @@ def check_range(request):
 
 
 def main():
-    h0 = ConcreteHandler0()
-    h1 = ConcreteHandler1()
-    h2 = ConcreteHandler2(FallbackHandler())
-    h0.successor = h1
-    h1.successor = h2
-
-    requests = [2, 5, 14, 22, 18, 3, 35, 27, 20]
-    for request in requests:
-        h0.handle(request)
+    """
+    >>> h0 = ConcreteHandler0()
+    >>> h1 = ConcreteHandler1()
+    >>> h2 = ConcreteHandler2(FallbackHandler())
+    >>> h0.successor = h1
+    >>> h1.successor = h2
+
+    >>> requests = [2, 5, 14, 22, 18, 3, 35, 27, 20]
+    >>> for request in requests:
+    ...     h0.handle(request)
+    request 2 handled in handler 0
+    request 5 handled in handler 0
+    request 14 handled in handler 1
+    request 22 handled in handler 2
+    request 18 handled in handler 1
+    request 3 handled in handler 0
+    end of chain, no handler for 35
+    request 27 handled in handler 2
+    request 20 handled in handler 2
+    """
 
 
 if __name__ == "__main__":
-    main()
-
-
-OUTPUT = """
-request 2 handled in handler 0
-request 5 handled in handler 0
-request 14 handled in handler 1
-request 22 handled in handler 2
-request 18 handled in handler 1
-request 3 handled in handler 0
-end of chain, no handler for 35
-request 27 handled in handler 2
-request 20 handled in handler 2
-"""
+    import doctest
+    doctest.testmod(optionflags=doctest.ELLIPSIS)

patterns/behavioral/chain_of_responsibility__py3.py

@@ -0,0 +1,118 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+"""
+*What is this pattern about?
+
+The Chain of responsibility is an object oriented version of the
+`if ... elif ... elif ... else ...` idiom, with the
+benefit that the condition–action blocks can be dynamically rearranged
+and reconfigured at runtime.
+
+This pattern aims to decouple the senders of a request from its
+receivers by allowing request to move through chained
+receivers until it is handled.
+
+Request receiver in simple form keeps a reference to a single successor.
+As a variation some receivers may be capable of sending requests out
+in several directions, forming a `tree of responsibility`.
+
+*TL;DR80
+Allow a request to pass down a chain of receivers until it is handled.
+"""
+
+import abc
+
+
+class Handler(metaclass=abc.ABCMeta):
+
+    def __init__(self, successor=None):
+        self.successor = successor
+
+    def handle(self, request):
+        """
+        Handle request and stop.
+        If can't - call next handler in chain.
+
+        As an alternative you might even in case of success
+        call the next handler.
+        """
+        res = self.check_range(request)
+        if not res and self.successor:
+            self.successor.handle(request)
+
+    @abc.abstractmethod
+    def check_range(self, request):
+        """Compare passed value to predefined interval"""
+
+
+class ConcreteHandler0(Handler):
+    """Each handler can be different.
+    Be simple and static...
+    """
+
+    @staticmethod
+    def check_range(request):
+        if 0 <= request < 10:
+            print("request {} handled in handler 0".format(request))
+            return True
+
+
+class ConcreteHandler1(Handler):
+    """... With it's own internal state"""
+
+    start, end = 10, 20
+
+    def check_range(self, request):
+        if self.start <= request < self.end:
+            print("request {} handled in handler 1".format(request))
+            return True
+
+
+class ConcreteHandler2(Handler):
+    """... With helper methods."""
+
+    def check_range(self, request):
+        start, end = self.get_interval_from_db()
+        if start <= request < end:
+            print("request {} handled in handler 2".format(request))
+            return True
+
+    @staticmethod
+    def get_interval_from_db():
+        return (20, 30)
+
+
+class FallbackHandler(Handler):
+    @staticmethod
+    def check_range(request):
+        print("end of chain, no handler for {}".format(request))
+        return False
+
+
+def main():
+    """
+    >>> h0 = ConcreteHandler0()
+    >>> h1 = ConcreteHandler1()
+    >>> h2 = ConcreteHandler2(FallbackHandler())
+    >>> h0.successor = h1
+    >>> h1.successor = h2
+
+    >>> requests = [2, 5, 14, 22, 18, 3, 35, 27, 20]
+    >>> for request in requests:
+    ...     h0.handle(request)
+    request 2 handled in handler 0
+    request 5 handled in handler 0
+    request 14 handled in handler 1
+    request 22 handled in handler 2
+    request 18 handled in handler 1
+    request 3 handled in handler 0
+    end of chain, no handler for 35
+    request 27 handled in handler 2
+    request 20 handled in handler 2
+    """
+
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod(optionflags=doctest.ELLIPSIS)

tests/test_outputs.py

@@ -10,8 +10,6 @@
 
 from patterns.behavioral.catalog import main as catalog_main
 from patterns.behavioral.catalog import OUTPUT as catalog_output
-from patterns.behavioral.chain_of_responsibility import main as chain_main
-from patterns.behavioral.chain_of_responsibility import OUTPUT as chain_output
 from patterns.behavioral.chaining_method import main as chaining_method_main
 from patterns.behavioral.chaining_method import OUTPUT as chaining_method_output
 from patterns.behavioral.command import main as command_main
@@ -38,7 +36,6 @@
                     reason="requires python3.4 or higher")
 @pytest.mark.parametrize("main,output", [
     (catalog_main, catalog_output),
-    (chain_main, chain_output),
     (chaining_method_main, chaining_method_output),
     (command_main, command_output),
     (iterator_main, iterator_output),