Fix read parquet import error message (#33361)

Author: jfcorbett

pandas/io/parquet.py

@@ -18,20 +18,23 @@ def get_engine(engine: str) -> "BaseImpl":
 
     if engine == "auto":
         # try engines in this order
-        try:
-            return PyArrowImpl()
-        except ImportError:
-            pass
+        engine_classes = [PyArrowImpl, FastParquetImpl]
 
-        try:
-            return FastParquetImpl()
-        except ImportError:
-            pass
+        error_msgs = ""
+        for engine_class in engine_classes:
+            try:
+                return engine_class()
+            except ImportError as err:
+                error_msgs += "\n - " + str(err)
 
         raise ImportError(
             "Unable to find a usable engine; "
             "tried using: 'pyarrow', 'fastparquet'.\n"
-            "pyarrow or fastparquet is required for parquet support"
+            "A suitable version of "
+            "pyarrow or fastparquet is required for parquet "
+            "support.\n"
+            "Trying to import the above resulted in these errors:"
+            f"{error_msgs}"
         )
 
     if engine == "pyarrow":
@@ -105,9 +108,7 @@ def write(
                 **kwargs,
             )
         else:
-            self.api.parquet.write_table(
-                table, path, compression=compression, **kwargs,
-            )
+            self.api.parquet.write_table(table, path, compression=compression, **kwargs)
 
     def read(self, path, columns=None, **kwargs):
         path, _, _, should_close = get_filepath_or_buffer(path)

pandas/tests/io/test_parquet.py

@@ -35,6 +35,7 @@
 except ImportError:
     _HAVE_FASTPARQUET = False
 
+
 pytestmark = pytest.mark.filterwarnings(
     "ignore:RangeIndex.* is deprecated:DeprecationWarning"
 )
@@ -223,6 +224,49 @@ def test_options_get_engine(fp, pa):
         assert isinstance(get_engine("fastparquet"), FastParquetImpl)
 
 
+def test_get_engine_auto_error_message():
+    # Expect different error messages from get_engine(engine="auto")
+    # if engines aren't installed vs. are installed but bad version
+    from pandas.compat._optional import VERSIONS
+
+    # Do we have engines installed, but a bad version of them?
+    pa_min_ver = VERSIONS.get("pyarrow")
+    fp_min_ver = VERSIONS.get("fastparquet")
+    have_pa_bad_version = (
+        False
+        if not _HAVE_PYARROW
+        else LooseVersion(pyarrow.__version__) < LooseVersion(pa_min_ver)
+    )
+    have_fp_bad_version = (
+        False
+        if not _HAVE_FASTPARQUET
+        else LooseVersion(fastparquet.__version__) < LooseVersion(fp_min_ver)
+    )
+    # Do we have usable engines installed?
+    have_usable_pa = _HAVE_PYARROW and not have_pa_bad_version
+    have_usable_fp = _HAVE_FASTPARQUET and not have_fp_bad_version
+
+    if not have_usable_pa and not have_usable_fp:
+        # No usable engines found.
+        if have_pa_bad_version:
+            match = f"Pandas requires version .{pa_min_ver}. or newer of .pyarrow."
+            with pytest.raises(ImportError, match=match):
+                get_engine("auto")
+        else:
+            match = "Missing optional dependency .pyarrow."
+            with pytest.raises(ImportError, match=match):
+                get_engine("auto")
+
+        if have_fp_bad_version:
+            match = f"Pandas requires version .{fp_min_ver}. or newer of .fastparquet."
+            with pytest.raises(ImportError, match=match):
+                get_engine("auto")
+        else:
+            match = "Missing optional dependency .fastparquet."
+            with pytest.raises(ImportError, match=match):
+                get_engine("auto")
+
+
 def test_cross_engine_pa_fp(df_cross_compat, pa, fp):
     # cross-compat with differing reading/writing engines