REGR: Fix reading old pickles from pandas 1.3.5

doc/source/whatsnew/v2.1.4.rst

@@ -13,7 +13,7 @@ including other versions of pandas.
 
 Fixed regressions
 ~~~~~~~~~~~~~~~~~
--
+- Fixed regression when trying to read a pickled pandas :class:`DataFrame` from pandas 1.3 (:issue:`55137`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/core/internals/blocks.py

@@ -2557,6 +2557,11 @@ def new_block(
     # - check_ndim/ensure_block_shape already checked
     # - maybe_coerce_values already called/unnecessary
     klass = get_block_type(values.dtype)
+
+    # Old pandas (<=1.3.0) will call this function with placements
+    # that aren't necessarily BlockPlacements when unpickling
+    if not isinstance(placement, BlockPlacement):
+        placement = BlockPlacement(placement)
     return klass(values, ndim=ndim, placement=placement, refs=refs)
 
 

pandas/tests/io/generate_legacy_storage_files.py

@@ -38,6 +38,10 @@
 import platform as pl
 import sys
 
+# Remove script directory from path, otherwise Python will try to
+# import the JSON test directory as the json module
+sys.path.pop(0)
+
 import numpy as np
 
 import pandas
@@ -314,7 +318,7 @@ def write_legacy_pickles(output_dir):
 
 def write_legacy_file():
     # force our cwd to be the first searched
-    sys.path.insert(0, ".")
+    sys.path.insert(0, "")
 
     if not 3 <= len(sys.argv) <= 4:
         sys.exit(
@@ -325,6 +329,9 @@ def write_legacy_file():
     output_dir = str(sys.argv[1])
     storage_type = str(sys.argv[2])
 
+    if not os.path.exists(output_dir):
+        os.mkdir(output_dir)
+
     if storage_type == "pickle":
         write_legacy_pickles(output_dir=output_dir)
     else: