BUG: Ensure headers is always defined

Author: bashtage

pandas_datareader/base.py

@@ -47,15 +47,15 @@ class _BaseReader(object):
     _format = "string"
 
     def __init__(
-            self,
-            symbols,
-            start=None,
-            end=None,
-            retry_count=3,
-            pause=0.1,
-            timeout=30,
-            session=None,
-            freq=None,
+        self,
+        symbols,
+        start=None,
+        end=None,
+        retry_count=3,
+        pause=0.1,
+        timeout=30,
+        session=None,
+        freq=None,
     ):
 
         self.symbols = symbols
@@ -72,6 +72,7 @@ def __init__(
         self.pause_multiplier = 1
         self.session = _init_session(session, retry_count)
         self.freq = freq
+        self.headers = None
 
     def close(self):
         """Close network session"""
@@ -149,7 +150,7 @@ def _get_response(self, url, params=None, headers=None):
         """
 
         # initial attempt + retry
-        if headers == None:
+        if headers is None:
             headers = self.headers
 
         pause = self.pause
@@ -227,14 +228,14 @@ class _DailyBaseReader(_BaseReader):
     """Base class for Google / Yahoo daily reader"""
 
     def __init__(
-            self,
-            symbols=None,
-            start=None,
-            end=None,
-            retry_count=3,
-            pause=0.1,
-            session=None,
-            chunksize=25,
+        self,
+        symbols=None,
+        start=None,
+        end=None,
+        retry_count=3,
+        pause=0.1,
+        session=None,
+        chunksize=25,
     ):
         super(_DailyBaseReader, self).__init__(
             symbols=symbols,
@@ -300,7 +301,7 @@ def _in_chunks(seq, size):
     """
     Return sequence in 'chunks' of size defined by size
     """
-    return (seq[pos: pos + size] for pos in range(0, len(seq), size))
+    return (seq[pos : pos + size] for pos in range(0, len(seq), size))
 
 
 class _OptionBaseReader(_BaseReader):
@@ -334,7 +335,7 @@ def get_put_data(self, month=None, year=None, expiry=None):
         raise NotImplementedError
 
     def get_near_stock_price(
-            self, above_below=2, call=True, put=False, month=None, year=None, expiry=None
+        self, above_below=2, call=True, put=False, month=None, year=None, expiry=None
     ):
         """
         ***Experimental***
@@ -343,7 +344,7 @@ def get_near_stock_price(
         raise NotImplementedError
 
     def get_forward_data(
-            self, months, call=True, put=False, near=False, above_below=2
+        self, months, call=True, put=False, near=False, above_below=2
     ):  # pragma: no cover
         """
         ***Experimental***