read_excel() modifies provided types dict when accessing file with duplicate column · Issue #42462 · pandas-dev/pandas (original) (raw)

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of pandas.
• (optional) I have confirmed this bug exists on the master branch of pandas.

test.xlsx :

import pandas as pd


types_dict = {'a': str,
             'b': str,
             'c': str,
             }


if __name__ == "__main__":
    df = pd.read_excel('./test.xlsx', dtype=type_dict)
    print(list(type_dict.keys()))

>> ['a', 'b', 'c', 'a.1']

Bug/Issue description:
When using dtype loading a .xlsx-file with a duplicate column into a dataframe modifies the provided types_dict / adds entries for duplicate columns.

It seems to me like the modification of the types_dict is an unwanted side effect.