Can you define the properties of a JSON schema without knowing the key names

Question

Going by the json schema definition json schema definition, I have been using the jsonschema python module for validation.

You can specify that an object contain an array of objects of animals for example,

{ 'type':'object',
    "properties":{
        'pets_list':{
            "type":"array",
            'items':{
                'type':'object',
                'properties':{
                    'name':{"type":"string"},
                    'mass':{"type":"number"},
                    'type':{"type":"string"},
                }
            }
        }    
    }    
}    

An Example Payload would be

{ 'pets_list':[{'name':'Charles',
            'mass':5,
            'type':'house mouse' },
        {'name':'Garfield',
            'mass':30,
            'type':'house cat'},
    ]
}

But what if I wanted to specify what those objects looked like in a slightly different keyed format.

{ 'pets_list':{
        'a7e8ad9':{'name':'Charles',
            'mass':5,
            'type':'house mouse' },
        '0a8d938':{'name':'Garfield',
            'mass':30,
            'type':'house cat'},
    }
}

I can't find any way in the spec to do this, since you do not know keys like 'a7e8ad9' in advance.