#198

added `freq` paramter `_BaseReader` and updated `def params` to accomodate monthly frequency data from the World Bank database.

Author: Kurt Forrester

pandas_datareader/base.py

@@ -19,30 +19,35 @@ class _BaseReader(object):
     """
     Parameters
     ----------
-        sym : string with a single Single stock symbol (ticker).
+        symbols : {str, List[str]}
+            String symbol of like of symbols
         start : string, (defaults to '1/1/2010')
-                Starting date, timestamp. Parses many different kind of date
-                representations (e.g., 'JAN-01-2010', '1/1/10', 'Jan, 1, 1980')
+            Starting date, timestamp. Parses many different kind of date
+            representations (e.g., 'JAN-01-2010', '1/1/10', 'Jan, 1, 1980')
         end : string, (defaults to today)
-                Ending date, timestamp. Same format as starting date.
+            Ending date, timestamp. Same format as starting date.
         retry_count : int, default 3
-                Number of times to retry query request.
+            Number of times to retry query request.
         pause : float, default 0.1
-                Time, in seconds, of the pause between retries.
+            Time, in seconds, of the pause between retries.
         session : Session, default None
-                requests.sessions.Session instance to be used
+            requests.sessions.Session instance to be used
+        freq : {str, None}
+            Frequency to use in select readers
     """
 
     _chunk_size = 1024 * 1024
     _format = 'string'
 
-    def __init__(self, symbols, start=None, end=None,
-                 retry_count=3, pause=0.1, timeout=30, session=None):
+    def __init__(self, symbols, start=None, end=None,  retry_count=3,
+                 pause=0.1, timeout=30, session=None, freq=None):
+
         self.symbols = symbols
 
         start, end = _sanitize_dates(start, end)
         self.start = start
         self.end = end
+        self.freq = freq
 
         if not isinstance(retry_count, int) or retry_count < 0:
             raise ValueError("'retry_count' must be integer larger than 0")

pandas_datareader/wb.py

@@ -116,7 +116,7 @@ class WorldBankReader(_BaseReader):
     _format = 'json'
 
     def __init__(self, symbols=None, countries=None,
-                 start=None, end=None,
+                 start=None, end=None, freq=None,
                  retry_count=3, pause=0.001, session=None, errors='warn'):
 
         if symbols is None:
@@ -125,7 +125,7 @@ def __init__(self, symbols=None, countries=None,
             symbols = [symbols]
 
         super(WorldBankReader, self).__init__(symbols=symbols,
-                                              start=start, end=end,
+                                              start=start, end=end, freq=freq,
                                               retry_count=retry_count,
                                               pause=pause, session=session)
 
@@ -155,6 +155,10 @@ def url(self):
 
     @property
     def params(self):
+        if self.freq == 'M':
+            return {'date': '{0}M{1:02d}:{2}M{3:02d}'.format(self.start.year,
+                    self.start.month, self.end.year, self.end.month),
+                    'per_page': 25000, 'format': 'json'}
         return {'date': '{0}:{1}'.format(self.start.year, self.end.year),
                 'per_page': 25000, 'format': 'json'}