add example app from IPython

missed in the repo split

examples/myapp.py

@@ -0,0 +1,99 @@
+"""A simple example of how to use traitlets.config.application.Application.
+
+This should serve as a simple example that shows how the traitlets config
+system works. The main classes are:
+
+* traitlets.config.Configurable
+* traitlets.config.SingletonConfigurable
+* traitlets.config.Config
+* traitlets.config.Application
+
+To see the command line option help, run this program from the command line::
+
+    $ python myapp.py -h
+
+To make one of your classes configurable (from the command line and config
+files) inherit from Configurable and declare class attributes as traits (see
+classes Foo and Bar below). To make the traits configurable, you will need
+to set the following options:
+
+* ``config``: set to ``True`` to make the attribute configurable.
+* ``shortname``: by default, configurable attributes are set using the syntax
+  "Classname.attributename". At the command line, this is a bit verbose, so
+  we allow "shortnames" to be declared. Setting a shortname is optional, but
+  when you do this, you can set the option at the command line using the
+  syntax: "shortname=value".
+* ``help``: set the help string to display a help message when the ``-h``
+  option is given at the command line. The help string should be valid ReST.
+
+When the config attribute of an Application is updated, it will fire all of
+the trait's events for all of the config=True attributes.
+"""
+
+from traitlets.config.configurable import Configurable
+from traitlets.config.application import Application
+from traitlets import (
+    Bool, Unicode, Int, List, Dict
+)
+
+
+class Foo(Configurable):
+    """A class that has configurable, typed attributes.
+
+    """
+
+    i = Int(0, config=True, help="The integer i.")
+    j = Int(1, config=True, help="The integer j.")
+    name = Unicode(u'Brian', config=True, help="First name.")
+
+
+class Bar(Configurable):
+
+    enabled = Bool(True, config=True, help="Enable bar.")
+
+
+class MyApp(Application):
+
+    name = Unicode(u'myapp')
+    running = Bool(False, config=True,
+                   help="Is the app running?")
+    classes = List([Bar, Foo])
+    config_file = Unicode(u'', config=True,
+                   help="Load this config file")
+
+    aliases = Dict(dict(i='Foo.i',j='Foo.j',name='Foo.name', running='MyApp.running',
+                        enabled='Bar.enabled', log_level='MyApp.log_level'))
+
+    flags = Dict(dict(enable=({'Bar': {'enabled' : True}}, "Enable Bar"),
+                  disable=({'Bar': {'enabled' : False}}, "Disable Bar"),
+                  debug=({'MyApp':{'log_level':10}}, "Set loglevel to DEBUG")
+            ))
+
+    def init_foo(self):
+        # Pass config to other classes for them to inherit the config.
+        self.foo = Foo(config=self.config)
+
+    def init_bar(self):
+        # Pass config to other classes for them to inherit the config.
+        self.bar = Bar(config=self.config)
+
+    def initialize(self, argv=None):
+        self.parse_command_line(argv)
+        if self.config_file:
+            self.load_config_file(self.config_file)
+        self.init_foo()
+        self.init_bar()
+
+    def start(self):
+        print("app.config:")
+        print(self.config)
+
+
+def main():
+    app = MyApp()
+    app.initialize()
+    app.start()
+
+
+if __name__ == "__main__":
+    main()