Added support for default overrides. This fixes #42

5 files changed, 92 insertions, 6 deletions

diff --git a/click/core.py b/click/core.py
index 3d1238b..1cc1898 100644
--- a/click/core.py
+++ b/click/core.py
@@ -47,10 +47,12 @@ class Context(object):
                                from environment variables is disabled.  This
                                does not affect manually set environment
                                variables which are always read.
+    :param default_map: a dictionary (like object) with default values
+                        for parameters.
     """
 
     def __init__(self, command, parent=None, info_name=None, obj=None,
-                 auto_envvar_prefix=None):
+                 auto_envvar_prefix=None, default_map=None):
         #: the parent context or `None` if none exists.
         self.parent = parent
         #: the :class:`Command` for this context.
@@ -72,6 +74,8 @@ class Context(object):
             obj = parent.obj
         #: the user object stored.
         self.obj = obj
+        #: A dictionary (like object) with defaults for parameters.
+        self.default_map = default_map
 
         # If there is no envvar prefix yet, but the parent has one and
         # the command on this level has a name, we can expand the envvar
@@ -149,6 +153,16 @@ class Context(object):
             self.obj = rv = object_type()
         return rv
 
+    def lookup_default(self, name):
+        """Looks up the default for a parameter name.  This by default
+        looks into the :attr:`default_map` if available.
+        """
+        if self.default_map is not None:
+            rv = self.default_map.get(name)
+            if callable(rv):
+                rv = rv()
+            return rv
+
     def fail(self, message):
         """Aborts the execution of the program with a specific error
         message.
@@ -362,6 +376,11 @@ class Command(object):
         :param extra: extra keyword arguments forwarded to the context
                       constructor.
         """
+        if 'default_map' not in extra:
+            default_map = None
+            if parent is not None and parent.default_map is not None:
+                default_map = parent.default_map.get(info_name)
+            extra['default_map'] = default_map
         ctx = Context(self, info_name=info_name, parent=parent, **extra)
         parser = self.make_parser(ctx)
         opts, args = parser.parse_args(args=args)
@@ -702,6 +721,8 @@ class Parameter(object):
     def consume_value(self, ctx, opts):
         value = opts.get(self.name)
         if value is None:
+            value = ctx.lookup_default(self.name)
+        if value is None:
             value = self.value_from_envvar(ctx)
         return value
 
diff --git a/docs/clickdoctools.py b/docs/clickdoctools.py
index 11488f8..b46841e 100644
--- a/docs/clickdoctools.py
+++ b/docs/clickdoctools.py
@@ -132,7 +132,7 @@ class ExampleRunner(object):
 
         def invoke(cmd, args=None, prog_name=None, prog_prefix='python ',
                    input=None, terminate_input=False, env=None,
-                   auto_envvar_prefix=None):
+                   **extra):
             if env:
                 for key, value in sorted(env.items()):
                     if ' ' in value:
@@ -152,8 +152,7 @@ class ExampleRunner(object):
                     input += '\xff'
             with isolation(input=input, env=env) as output:
                 try:
-                    cmd.main(args=args, prog_name=prog_name,
-                             auto_envvar_prefix=auto_envvar_prefix)
+                    cmd.main(args=args, prog_name=prog_name, **extra)
                 except SystemExit:
                     pass
                 buffer.extend(output.getvalue().splitlines())
diff --git a/docs/commands.rst b/docs/commands.rst
index 38e37b1..e4a12cd 100644
--- a/docs/commands.rst
+++ b/docs/commands.rst
@@ -254,3 +254,50 @@ And what it looks like:
     invoke(cli, prog_name='cli', args=['--help'])
 
 In case a command exists on more than one source, the first source wins.
+
+Overriding Defaults
+-------------------
+
+By default the default value for a parameter is pulled from the
+``default`` flag that is provided when it's defined.  But that's not the
+only place defaults can be loaded from.  The other place is the
+:attr:`Context.default_map` (a dictionary) on the context.  This allows
+defaults to be loaded from a config file to override the regular defaults.
+
+This is useful if you plug in some commands from another package but
+you're not satisfied with the defaults.
+
+The default map can be nested arbitrarily for each subcommand and be
+provided when the script is invoked.  Alternatively it can also be
+overriden at any point by commands.  For instance a toplevel command could
+load the defaults from a config file.
+
+Example usage:
+
+.. click:example::
+
+    import click
+
+    @click.group()
+    def cli():
+        pass
+
+    @cli.command()
+    @click.option('--port', default=8000)
+    def runserver(port):
+        click.echo('Serving on http://127.0.0.1:%d/' % port)
+
+    if __name__ == '__main__':
+        cli(default_map={
+            'runserver': {
+                'port': 5000
+            }
+        })
+
+.. click:run::
+
+    invoke(cli, prog_name='cli', args=['runserver'], default_map={
+        'runserver': {
+            'port': 5000
+        }
+    })
diff --git a/tests/conftest.py b/tests/conftest.py
index 1d2e0b9..c46b982 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -118,13 +118,14 @@ class CliRunner(object):
             click.termui.visible_prompt_func = old_visible_prompt_func
             click.termui.hidden_prompt_func = old_hidden_prompt_func
 
-    def invoke(self, cli, args):
+    def invoke(self, cli, args, **extra):
         with self.isolation() as out:
             exception = None
             exit_code = 0
 
             try:
-                cli.main(args=args, prog_name=cli.name or 'root')
+                cli.main(args=args, prog_name=cli.name or 'root',
+                         **extra)
             except SystemExit as e:
                 if e.code != 0:
                     exception = e
diff --git a/tests/test_commands.py b/tests/test_commands.py
index 03a4e10..9194991 100644
--- a/tests/test_commands.py
+++ b/tests/test_commands.py
@@ -38,3 +38,21 @@ def test_auto_shorthelp(runner):
         r'Commands:\n\s+'
         r'long\s+This is a long text that is too long to show\.\.\.\n\s+'
         r'short\s+This is a short text\.', result.output) is not None
+
+
+def test_default_maps(runner):
+    @click.group()
+    def cli():
+        pass
+
+    @cli.command()
+    @click.option('--name', default='normal')
+    def foo(name):
+        click.echo(name)
+
+    result = runner.invoke(cli, ['foo'], default_map={
+        'foo': {'name': 'changed'}
+    })
+
+    assert not result.exception
+    assert result.output == 'changed\n'