Move class inspection code to utils

tests/utils/test_main.py

@@ -108,4 +108,19 @@ def test_get_password_from_system_keyring(monkeypatch, resources_to_test):
     assert netrc_calls == [hostname]
 
 
+def test_get_class_init_args():
+    class Foobar(object):
+        def __init__(self, foo, bar, baz=None):
+            pass
 
+    all, required = utils.get_class_init_args(Foobar)
+    assert all == {'foo', 'bar', 'baz'}
+    assert required == {'foo', 'bar'}
+
+
+def test_get_class_init_args_on_storage():
+    from vdirsyncer.storage.memory import MemoryStorage
+
+    all, required = utils.get_class_init_args(MemoryStorage)
+    assert not all
+    assert not required

vdirsyncer/cli.py

@@ -15,7 +15,7 @@ import argvard
 
 from .storage import storage_names
 from .sync import sync, StorageEmpty
-from .utils import expand_path, parse_options, split_dict
+from .utils import expand_path, parse_options, split_dict, get_class_init_args
 
 import vdirsyncer.log as log
 
@@ -123,7 +123,7 @@ def storage_instance_from_config(config, description=None):
     try:
         return cls(**config)
     except Exception:
-        all, required = get_init_args(cls)
+        all, required = get_class_init_args(cls)
         given = set(config)
         missing = required - given
         invalid = given - all
@@ -147,20 +147,6 @@ def storage_instance_from_config(config, description=None):
         sys.exit(1)
 
 
-def get_init_args(cls):
-    from vdirsyncer.storage.base import Storage
-    import inspect
-
-    if cls is Storage:
-        return set(), set()
-
-    spec = inspect.getargspec(cls.__init__)
-    all = set(spec.args[1:])
-    required = set(spec.args[1:-len(spec.defaults)])
-    supercls = next(x for x in cls.__mro__[1:] if hasattr(x, '__init__'))
-    s_all, s_required = get_init_args(supercls)
-
-    return all | s_all, required | s_required
 
 
 def main():

vdirsyncer/utils/__init__.py

@@ -251,3 +251,28 @@ class safe_write(object):
 
 def get_etag_from_file(fpath):
     return '{:.9f}'.format(os.path.getmtime(fpath))
+
+
+def get_class_init_args(cls):
+    '''
+    Get args which are taken during class initialization. Assumes that all
+    classes' __init__ calls super().__init__ with the rest of the arguments.
+
+    :param cls: The class to inspect.
+    :returns: (all, required), where ``all`` is a set of all arguments the
+        class can take, and ``required`` is the subset of arguments the class
+        requires.
+    '''
+    import inspect
+
+    if cls is object:
+        return set(), set()
+
+    spec = inspect.getargspec(cls.__init__)
+    all = set(spec.args[1:])
+    required = set(spec.args[1:-len(spec.defaults or ())])
+    supercls = next(getattr(x.__init__, '__objclass__', x)
+                    for x in cls.__mro__[1:])
+    s_all, s_required = get_class_init_args(supercls)
+
+    return all | s_all, required | s_required