Raise NotImplementedError if pandas is not installed

tablib/formats/_df.py

@@ -10,7 +10,10 @@ if sys.version_info[0] > 2:
 else:
     from cStringIO import StringIO as BytesIO
 
-from pandas import DataFrame
+try:
+    from pandas import DataFrame
+except ImportError:
+    DataFrame = None
 
 import tablib
 
@@ -21,6 +24,8 @@ extensions = ('df', )
 
 def detect(stream):
     """Returns True if given stream is a DataFrame."""
+    if DataFrame is None:
+        return False
     try:
         DataFrame(stream)
         return True
@@ -30,6 +35,10 @@ def detect(stream):
 
 def export_set(dset, index=None):
     """Returns DataFrame representation of DataBook."""
+    if DataFrame is None:
+        raise NotImplementedError(
+            'DataFrame Format requires `pandas` to be installed.'
+            ' Try `pip install tablib[pandas]`.')
     dataframe = DataFrame(dset.dict, columns=dset.headers)
     return dataframe