Error while trying to load a JSON object with python 3

customerData = {   
 "Joe": {"visits": 1},  
 "Carol":  {"visits": 2},  
 "Howard": {"visits": 3},  
 "Carrie": {"visits": 4}  
}

is Python code that defines a dictionary. If you had

customerJSON = """{   
 "Joe": {"visits": 1},  
 "Carol":  {"visits": 2},  
 "Howard": {"visits": 3},  
 "Carrie": {"visits": 4}  
}"""

you would have a string that contains a JSON object to be parsed. (Yes, there is a lot of overlap between Python syntax and JSON syntax.

assert customerData == json.loads(customerJSON)

would pass.)

Note, though, that not all valid Python resembles valid JSON.

Here are three different JSON strings that encode the same object:

json_strs = [
 "{'foo': 'bar'}",  # invalid JSON, uses single quotes
 '{"foo": "bar"}',  # valid JSON, uses double quotes
 '{foo: "bar"}'     # valid JSON, quotes around key can be omitted
]

You can observe that all(json.loads(x) == {'foo': 'bar'} for x in json_strs) is true, since all three strings encode the same Python dict.

Conversely, we can define three Python dicts, the first two of which are identical.

json_str = json_strs[0]  # Just to pick one
foo = ...  # Some value
dicts = [
  {'foo': 'bar'},     # valid Python dict
  {"foo": "bar"},     # valid Python dict
  {foo: "bar"}        # valid Python dict *if* foo is a hashable value
                      # and not necessarily 
]

It is true that dicts[0] == dicts[1] == json.loads(json_str). However, dicts[2] == json.loads(json_str) is only true if foo == "foo".