Sympifyin string with superscripts

[darmend...@outlook.com]

I am trying to sympify a string like these

    str1="a^0_0"

    ns={}

    ns['a^0_0']=Symbol('a^0_0')

    pprint(sympify(str1,locals=ns))

But I get the following error

    Traceback (most recent call last):

      File "cuaterniones_basic.py", line 114, in <module>

        pprint(sympify(str1,locals=ns))

      File "/usr/local/lib/python2.7/dist-packages/sympy/core/sympify.py", line 356, in sympify

        raise SympifyError('could not parse %r' % a, exc)

    sympy.core.sympify.SympifyError: Sympify of expression 'could not parse u'a^0_0'' failed, because of exception being raised:

    SyntaxError: invalid syntax (<string>, line 1

How can get the symbol I want?

[Leonid Kovalev]

To avoid duplication of effort, it should be mentioned that this was
also posted on Stack Overflow:
https://stackoverflow.com/questions/48454848/sympy-sympifying-strings-containing-expressions-with-superscripts