Human: check df index type. Assistant: 
Here is a Python function to check df index type

import pandas as pd

def check_df_index_type(df):
    """
    Check df index type
    """
    if not isinstance(df.index, pd.core.indexes.base.Index):
        raise ValueError("df.index must be a pandas Index object")

# Enter the dataframe
df = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]})

# Calling the function
print((check_df_index_type(df)))

#Example Output
# None

#Remember to inspect code for bugs.