added freq parameter to enable explicit querying of monthly, quarterly and annual data from World Bank.

also added test for monthly and quarterly.

Author: Kurt Forrester

pandas_datareader/base.py

@@ -47,7 +47,6 @@ def __init__(self, symbols, start=None, end=None,  retry_count=3,
         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/tests/test_wb.py

@@ -214,3 +214,65 @@ def test_wdi_get_indicators(self):
             # assert_index_equal doesn't exists
             assert result.columns.equals(exp_col)
             assert len(result) > 10000
+
+    def test_wdi_download_monthly(self):
+
+        expected = {'COPPER': {('World', '2012M01'): 8040.47,
+                               ('World', '2011M12'): 7565.48,
+                               ('World', '2011M11'): 7581.02,
+                               ('World', '2011M10'): 7394.19,
+                               ('World', '2011M09'): 8300.14,
+                               ('World', '2011M08'): 9000.76,
+                               ('World', '2011M07'): 9650.46,
+                               ('World', '2011M06'): 9066.85,
+                               ('World', '2011M05'): 8959.90,
+                               ('World', '2011M04'): 9492.79,
+                               ('World', '2011M03'): 9503.36,
+                               ('World', '2011M02'): 9867.60,
+                               ('World', '2011M01'): 9555.70}}
+        expected = pd.DataFrame(expected)
+        # Round, to ignore revisions to data.
+        expected = np.round(expected, decimals=-3)
+        expected = expected.sort_index()
+        cntry_codes = 'ALL'
+        inds = 'COPPER'
+        result = download(country=cntry_codes, indicator=inds,
+                          start=2011, end=2012, freq='M',errors='ignore')
+        result = result.sort_index()
+        result = np.round(result, decimals=-3)
+
+        expected.index.names = ['country', 'year']
+        tm.assert_frame_equal(result, expected)
+
+        result = WorldBankReader(inds, countries=cntry_codes,
+                                 start=2011, end=2012, freq='M', errors='ignore').read()
+        result = result.sort_index()
+        result = np.round(result, decimals=-3)
+        tm.assert_frame_equal(result, expected)
+
+    def test_wdi_download_quarterly(self):
+
+        expected = {'DT.DOD.PUBS.CD.US': {('Albania', '2012Q1'): 3240539817.18,
+                                          ('Albania', '2011Q4'): 3213979715.15,
+                                          ('Albania', '2011Q3'): 3187681048.95,
+                                          ('Albania', '2011Q2'): 3248041513.86,
+                                          ('Albania', '2011Q1'): 3137210567.92,}}
+        expected = pd.DataFrame(expected)
+        # Round, to ignore revisions to data.
+        expected = np.round(expected, decimals=-3)
+        expected = expected.sort_index()
+        cntry_codes = 'ALB'
+        inds = 'DT.DOD.PUBS.CD.US'
+        result = download(country=cntry_codes, indicator=inds,
+                          start=2011, end=2012, freq='Q',errors='ignore')
+        result = result.sort_index()
+        result = np.round(result, decimals=-3)
+
+        expected.index.names = ['country', 'year']
+        tm.assert_frame_equal(result, expected)
+
+        result = WorldBankReader(inds, countries=cntry_codes,
+                                 start=2011, end=2012, freq='Q', errors='ignore').read()
+        result = result.sort_index()
+        result = np.round(result, decimals=-1)
+        tm.assert_frame_equal(result, expected)

pandas_datareader/wb.py

@@ -125,7 +125,7 @@ def __init__(self, symbols=None, countries=None,
             symbols = [symbols]
 
         super(WorldBankReader, self).__init__(symbols=symbols,
-                                              start=start, end=end, freq=freq,
+                                              start=start, end=end,
                                               retry_count=retry_count,
                                               pause=pause, session=session)
 
@@ -144,6 +144,12 @@ def __init__(self, symbols=None, countries=None,
                 warnings.warn('Non-standard ISO '
                               'country codes: %s' % tmp, UserWarning)
 
+        freq_symbols = ['M','Q','A', None]
+        if freq not in freq_symbols:
+            msg = 'The frequency `{0}` is not in the accepted list.'.format(freq)
+            raise ValueError(msg)
+
+        self.freq = freq
         self.countries = countries
         self.errors = errors
 
@@ -159,8 +165,14 @@ def params(self):
             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'}
+        if self.freq == 'Q':
+            return {'date': '{0}Q{1}:{2}Q{3}'.format(self.start.year,
+                    divmod(self.start.month-1,3)[0]+1, self.end.year,
+                    divmod(self.end.month-1,3)[0]+1),'per_page': 25000,
+                    'format': 'json'}
+        if self.freq is None or self.freq == 'A':
+            return {'date': '{0}:{1}'.format(self.start.year, self.end.year),
+                    'per_page': 25000, 'format': 'json'}
 
     def read(self):
         try:
@@ -335,7 +347,7 @@ def search(self, string='gdp.*capi', field='name', case=False):
         return out
 
 
-def download(country=None, indicator=None, start=2003, end=2005,
+def download(country=None, indicator=None, start=2003, end=2005, freq=None,
              errors='warn', **kwargs):
     """
     Download data series from the World Bank's World Development Indicators
@@ -361,6 +373,11 @@ def download(country=None, indicator=None, start=2003, end=2005,
     end: int
         Last year of the data series (inclusive)
 
+    freq: str
+        frequency or periodicity of the data to be retrieved (e.g. 'M' for
+        monthly, 'Q' for quarterly, and 'A' for annual). None defaults to
+        annual.
+
     errors: str {'ignore', 'warn', 'raise'}, default 'warn'
         Country codes are validated against a hardcoded list.  This controls
         the outcome of that validation, and attempts to also apply
@@ -379,7 +396,7 @@ def download(country=None, indicator=None, start=2003, end=2005,
 
     """
     return WorldBankReader(symbols=indicator, countries=country,
-                           start=start, end=end, errors=errors,
+                           start=start, end=end, freq=freq, errors=errors,
                            **kwargs).read()