thsU= {
    'success': 0,
    'return': {
        '0000000000': {
            'pair': '', 'type': '', 'amount': 0.0, 'rate': 0.0, 'timestamp_created': 0000000, 'status': 0
        }
    }
}

vals = list(thsU['return'].values())
print(vals)
print(vals[0]['rate'])

In [5]: dictionary = {
   ...:     'success': 0,
   ...:     'return': {
   ...:         '0000000000': {
   ...:             'pair': '', 'type': '', 'amount': 0.0, 'rate': 0.0, 'timestamp_created': 0000000, 'status
   ...: ': 0
   ...:         }
   ...:     }
   ...: }

In [6]: dictionary['return'][list(dictionary['return'].keys())[0]]['rate']
Out[6]: 0.0

assert len(some_dict['return']) == 1

[nested_dict] = some_dict['return'].values()
print(nested_dict['rate'])  # -> 0.0

nested_dict = next(iter(some_dict['return'].values()))
print(nested_dict['rate'])  # -> 0.0