If you read the documentation for urllib.parse.urlencode [1], you'll
see that it says:

    The value element in itself can be a sequence and in that case, if
    the optional parameter doseq is evaluates to True, individual
    key=value pairs separated by '&' are generated for each element of
    the value sequence for the key.

So you need to write:

    >>> urllib.parse.urlencode(thisDict, doseq=True)
    'SomeVar3=ghi&SomeVar1=abc&SomeVar2=def'

[1]: https://docs.python.org/3/library/urllib.parse.html#urllib.parse.urlencode