Merge pull request #172 from cclauss/patch-1

Use ==/!= to compare str, bytes, and int literals

alpha_vantage/alphavantage.py

@@ -50,7 +50,7 @@ def __init__(self, key=None, output_format='json',
                              'https://www.alphavantage.co/support/#api-key')
         self.key = key
         self.output_format = output_format
-        if self.output_format is 'pandas' and not _PANDAS_FOUND:
+        if self.output_format == 'pandas' and not _PANDAS_FOUND:
             raise ValueError("The pandas library was not found, therefore can "
                              "not be used as an output format, please install "
                              "manually")