Fix variable name.

libcodonusage/__init__.py

 __copyright__ = "Copyright (C) 2022-2023 Blaise Li"
 __licence__ = "GNU GPLv3"
-__version__ = "0.27.2"
+__version__ = "0.27.3"
 from .libcodonusage import (
     aa2colour,
     aa_usage,

libcodonusage/libcodonusage.py

@@ -507,11 +507,11 @@ def check_aa_codon_columns(table):
     Check that the columns of *table* correspond to (aa, codon) pairs.
     """
     msg = "Codon proportions table should have two levels: 'aa' and 'codon'"
-    if codon_proportions_by_aa.columns.nlevels !=2:
+    if table.columns.nlevels !=2:
         raise ValueError(msg)
-    if codon_proportions_by_aa.columns.names[0] != "aa":
+    if table.columns.names[0] != "aa":
         raise ValueError(msg)
-    if codon_proportions_by_aa.columns.names[1] != "codon":
+    if table.columns.names[1] != "codon":
         raise ValueError(msg)