Merge pull request #238 from tcmitchell/visitor-example

Add an object oriented visitor example

examples/visitor.py

@@ -0,0 +1,96 @@
+import argparse
+import logging
+from typing import Any
+
+import sbol3
+
+# This example demonstrates how to adapt the functional vistor pattern
+# in pySBOL3 to an object oriented visitor pattern similar to
+# https://refactoring.guru/design-patterns/visitor/python/example or
+# https://en.wikipedia.org/wiki/Visitor_pattern#Python_example
+
+# Usage:
+#
+#    python3 visitor.py [-d] SBOL_FILE_NAME
+
+
+class SBOLVisitor:
+    """A base class for visitor pySBOL3 visitors.
+    """
+
+    def __call__(self, sbol_object: sbol3.Identified):
+        """This method is invoked on every SBOL object that is visited. The
+        visit is then dispatched to a type-specific method. If no
+        type-specific method exists, `visit_fallback` is invoked with
+        the SBOL object. The default implementation of
+        `visit_fallback` does nothing.
+
+        """
+        method_name = self._method_name(sbol_object)
+        try:
+            getattr(self, method_name)(sbol_object)
+        except AttributeError:
+            self.visit_fallback(sbol_object)
+
+    def _method_name(self, thing: Any) -> str:
+        """Generates a visitor method name for a given object. Override this
+        method if you want a different conversion from object to
+        method name.
+
+        """
+        qualname = type(thing).__qualname__.replace(".", "_")
+        return f'visit_{qualname}'
+
+    def visit_fallback(self, sbol_object: sbol3.Identified):
+        """Visit an object that doesn't have a specific method for its type.
+        Override this method to catch objects that do not have a
+        specific visit method defined for them.
+
+        """
+        pass
+
+
+class MyVisitor(SBOLVisitor):
+    """An example visitor.
+
+    """
+
+    def visit_Component(self, c):
+        print(f'Visited Component {c.identity}')
+
+    def visit_SubComponent(self, sc):
+        print(f'Visited SubComponent {sc.identity}')
+
+    def visit_fallback(self, sbol_object: sbol3.Identified):
+        type_name = type(sbol_object).__qualname__
+        logging.debug(f'Fallback visit of {type_name} {sbol_object.identity}')
+
+
+def parse_args(args=None):
+    parser = argparse.ArgumentParser()
+    parser.add_argument("inputfile", metavar="SBOL_FILE")
+    parser.add_argument('-d', '--debug', action='store_true')
+    args = parser.parse_args(args)
+    return args
+
+
+def init_logging(debug=False):
+    msg_format = '%(asctime)s %(levelname)s %(message)s'
+    date_format = '%m/%d/%Y %H:%M:%S'
+    level = logging.INFO
+    if debug:
+        level = logging.DEBUG
+    logging.basicConfig(format=msg_format, datefmt=date_format, level=level)
+
+
+def main(argv=None):
+    args = parse_args(argv)
+    init_logging(args.debug)
+    doc = sbol3.Document()
+    doc.read(args.inputfile)
+    my_visitor = MyVisitor()
+    doc.accept(my_visitor)
+
+
+if __name__ == '__main__':
+    main()