How to emulate file opened in text mode in Python

You can use BytesIO instead:

import io

s = "αβγδεζηθικλμνξoπρστυφχψω"
with io.BytesIO(s.encode("utf-8")) as f:
    f.seek(8)
    print(f.read(8).decode("utf-8"))

You can use BytesIO and TextIOWrapper to emulate the behavior of a real file:

text = 'αβγδεζηθικλμνξoπρστυφχψω'

with io.BytesIO(text.encode('utf8')) as binary_file:
    with io.TextIOWrapper(binary_file, encoding='utf8') as file_obj:
        file_obj.seek(8)
        print(file_obj.read(8))
        # εζηθικλμ