modest refactor of attr validator code

mgship/cli.py

@@ -8,7 +8,7 @@
 from mgship import mgship
 from mgship.destination import csv, json
 from mgship.cliparam import DateTime, Loglevel
-from mgship.util import utctimestamp, validate_past
+from mgship.util import utctimestamp, is_past
 from mgship.log import logger
 
 
@@ -26,7 +26,7 @@ def to_timestamp(ctx, param, value):
     try:
         value = utctimestamp(value)
         if ctx.info_name == 'archive':
-            validate_past(value)
+            is_past(value)
         return value
     except (TypeError, ValueError) as e:
         logger.debug("bad timestamp parameter", exc_info=True)

mgship/mgship.py

@@ -3,19 +3,32 @@
 from __future__ import absolute_import
 import attr
 
+from functools import wraps
+
 from mgship.api import Client
 from mgship.events import mg_past_events
-from mgship.util import validate_past
+from mgship.util import is_past
 from mgship.log import logger
 
 
+def mg_field_validator(wrapped):
+    """Convert a simple validator method to a attr.ib validator.
+
+    Given a method which accepts a value and possibly raises ValueError
+    create a attr compatible validator that accepts empty values.
+    """
+    @attr.validators.optional
+    @wraps(wrapped)
+    def wrapper(*args, **kwargs):
+        return wrapped(*args[2:], **kwargs)
+    return wrapper
+
+
 @attr.s
 class Archive(object):
     """Ship all existing events."""
     dest = attr.ib()
-    begin = attr.ib(default=None,
-                    validator=attr.validators.optional(
-                        lambda i, a, v: validate_past(v)))
+    begin = attr.ib(default=None, validator=mg_field_validator(is_past))
     _client = attr.ib(default=attr.Factory(Client), repr=False)
     _filtered_params = ['dest', '_client']
 

mgship/util.py

@@ -7,7 +7,7 @@
 from datetime import datetime, timedelta
 
 __all__ = ['utctimestamp', 'timenow', 'timeago', 'fromtimestamp',
-           'validate_past']
+           'is_past']
 
 
 def utctimestamp(now=None):
@@ -28,7 +28,7 @@ def timeago(**kwargs):
     return timenow() - timedelta(**kwargs)
 
 
-def validate_past(value):
+def is_past(value):
     """Validator for timestamps in the past.
 
     Raises ValueError if value is not a timestamp that represents