DEV: Adds a script to test data saved as msgpacks.

The loader_tool currently facilitates:
- Finding the last date in each source
- Forcing a complete reload of benchmark and treasury.
- Manipulating the msgpacks so that trailing dates are dropped,
  so that the condition for an update can be recreated.

This is intended to make it easier to test the update logic added
by @rday in PR #88

zipline/data/loader_tool.py

@@ -0,0 +1,118 @@
+#
+# Copyright 2013 Quantopian, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Module for manipulating and verifying the msgpack files.
+
+Intended for testing update logic of msgpack files.
+"""
+import argparse
+import datetime
+import functools
+import itertools
+import os
+import sys
+
+import msgpack
+
+import zipline.data.loader as loader
+from zipline.utils.date_utils import tuple_to_date
+
+
+DATA_SOURCES = {
+    'benchmark': {
+        'filename': '^GSPC_benchmark.msgpack',
+        'download_func':
+        functools.partial(loader.dump_benchmarks, '^GSPC')
+    },
+    'treasury': {
+        'filename': 'treasury_curves.msgpack',
+        'download_func': loader.dump_treasury_curves
+    }
+}
+
+
+def last_date(source_name, args):
+    data = loader.get_saved_data(DATA_SOURCES[source_name]['filename'])
+    date = tuple_to_date(data[-1][0])
+    print "Last saved {source_name} date is {date}".format(
+        source_name=source_name, date=date)
+
+
+def drop_before_date(source_name, last_date):
+    """
+    Loads the msgpack file for the given @source_name and drops values
+    up to @last_date.
+
+    Used so that we can test logic that updates the msgpack's to download
+    current data if the data isn't current enough.
+    """
+    filename = DATA_SOURCES[source_name]['filename']
+    data = loader.get_saved_data(filename)
+
+    filtered_data = itertools.takewhile(
+        lambda x: tuple_to_date(x[0]).date() <= last_date.date(), data)
+
+    with loader.get_datafile(filename, mode='wb') as fp:
+        fp.write(msgpack.dumps(list(filtered_data)))
+
+
+def drop_wrapper(source_name, args):
+    if not args.last_date:
+        sys.exit("Last date must be supplied for drop.")
+    last_date = datetime.datetime.strptime(args.last_date, "%Y-%m-%d")
+
+    drop_before_date(source_name, last_date)
+
+
+def force_load(source_name, args):
+    if not os.path.exists(loader.DATA_PATH):
+        os.makedirs(loader.DATA_PATH)
+
+    filename = (DATA_SOURCES[source_name]['filename'])
+
+    filepath = os.path.join(loader.DATA_PATH, filename)
+
+    os.remove(filepath)
+    DATA_SOURCES[source_name]['download_func']()
+
+
+ACTIONS = {
+    'last_date': last_date,
+    'drop_before_date': drop_wrapper,
+    'force_load': force_load
+}
+
+
+def _make_parser():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('action')
+    parser.add_argument('--data-source',
+                        action='append',
+                        choices=DATA_SOURCES.keys(),
+                        default=DATA_SOURCES.keys())
+    parser.add_argument('--last-date')
+    return parser
+
+
+def main():
+    parser = _make_parser()
+    args = parser.parse_args()
+
+    for source_name in args.data_source:
+        ACTIONS[args.action](source_name, args)
+
+if __name__ == "__main__":
+    main()