Add module name to expected meta error message (#4499)

* Add module name to expected meta error message

* handle builtins and None in typename

dask/dataframe/core.py

@@ -27,7 +27,7 @@
 from ..context import globalmethod
 from ..utils import (random_state_data, pseudorandom, derived_from, funcname,
                      memory_repr, put_lines, M, key_split, OperatorMethodMixin,
-                     is_arraylike)
+                     is_arraylike, typename)
 from ..array.core import Array, normalize_arg
 from ..blockwise import blockwise, Blockwise
 from ..base import DaskMethodsMixin, tokenize, dont_optimize, is_dask_collection
@@ -90,7 +90,7 @@ def __init__(self, dsk, name, meta, divisions=None):
         meta = make_meta(meta)
         if is_dataframe_like(meta) or is_series_like(meta) or is_index_like(meta):
             raise TypeError("Expected meta to specify scalar, got "
-                            "{0}".format(type(meta).__name__))
+                            "{0}".format(typename(type(meta))))
         self._meta = meta
 
     def __dask_graph__(self):
@@ -253,8 +253,8 @@ def __init__(self, dsk, name, meta, divisions):
         meta = make_meta(meta)
         if not isinstance(meta, self._partition_type):
             raise TypeError("Expected meta to specify type {0}, got type "
-                            "{1}".format(self._partition_type.__name__,
-                                         type(meta).__name__))
+                            "{1}".format(typename(self._partition_type),
+                                         typename(type(meta))))
         self._meta = meta
         self.divisions = tuple(divisions)
 

dask/dataframe/tests/test_dataframe.py

@@ -3380,3 +3380,12 @@ def test_has_parallel_type():
     assert has_parallel_type(pd.DataFrame())
     assert has_parallel_type(pd.Series())
     assert not has_parallel_type(123)
+
+
+def test_meta_error_message():
+    with pytest.raises(TypeError) as info:
+        dd.DataFrame({('x', 1): 123}, 'x', pd.Series(), [None, None])
+
+    assert 'Series' in str(info.value)
+    assert 'DataFrame' in str(info.value)
+    assert 'pandas' in str(info.value)

dask/utils.py

@@ -558,6 +558,25 @@ def funcname(func):
         return str(func)
 
 
+def typename(typ):
+    """
+    Return the name of a type
+
+    Examples
+    --------
+    >>> typename(int)
+    'int'
+
+    >>> from dask.core import literal
+    >>> typename(literal)
+    'dask.core.literal'
+    """
+    if not typ.__module__ or typ.__module__ == 'builtins':
+        return typ.__name__
+    else:
+        return typ.__module__ + '.' + typ.__name__
+
+
 def ensure_bytes(s):
     """ Turn string or bytes to bytes