CODEWITHSUNDEEP
python-3.xclass
Erik Steiner
Erik Steiner

Reputation: 601

Python: How to store data in class and inherit

I am pretty new to classes and I already wrote a class for doing some Pandas operations.

However I noticed, that working with objects can result in objects that don't know the original definitions. So I came to @classmethod, but I don't have an idea of how to use them.

Goal of my class:
I want to write a Permission class. It should load/write a json-file and one should be able to add more permissions.

EDIT:
After some reading I ended up with a staticmethod and a __init__ that load the file during their initialization.

class Permission:
    data = None

    def __init__(self, path):
        if Permission.data is None:
            self.read_permissions(path)

    @staticmethod
    def read_permissions(path):
        try:
            with open(path, 'r') as read_file:
                Permission.data = json.load(read_file)
        except FileNotFoundError as e:
            logging.error(e)
            sys.exit(1)

    def add_permissions(self, group, level, permissions):
        self.data['groups'].append({
            'group': group,
            'level': level,
            'permissions': permissions
        })

So I can use the class like this:

json_path = 'C:\\data\\test.json'
test_perm = Permission(json_path)

print(test_perm.data)
{'groups': [{'group': 'common', 'permissions': {'select_sample_x': True, 'select_sample_y': True, 'assign_x': False, 'request_y': True}}]}

test_perm.add_permissions('guys', 10, {'can_do_icecream': False, 'can_do_nothing': True})

print(test_perm.data)
{'groups': [{'group': 'pkf_common', 'permissions': {'select_sample_debitor': True, 'select_sample_creditor': True, 'assign_third_party_confirmation': False, 'request_reporting': True}}, {'group': 'guys', 'level': 10, 'permissions': {'can_do_icecream': False, 'can_do_nothing': True}}]}

Upvotes: 1

Views: 486

Answers (1)

doctorlove
doctorlove

Reputation: 19232

Since most of your methods are @classmethod, you might find it easy to just use functions.

You can read permissions, and maybe let the calling code decide what to do on an error:

def read_permissions(path):
        with open(path, 'r') as read_file:
            return json.load(read_file)

Previously, you returned cls(path).data so the calling code would have to keep hold of the data.

Once you have one set of permissions, called data returned from this, you can use your add_permissions to append to data['groups'], without using classes at all.

An alternative is to load some data when you make a class instance, and use that instance from then one:

class Permissions:
    def __init__(self, path):
        self.path = path
        self.data = []
        try:
            with open(path, 'r') as read_file:
                self.data = json.load(read_file) #<--- store in instance
        except FileNotFoundError as e:
            logging.error(e)
            sys.exit(1) #slightly extreme, but up to you

    def write_permissions(self, filename): #note the new filename
        with open(filename, 'w') as outfile:
            json.dump(self.data, outfile, indent=4)

    def add_permissions(self, path, group, permissions):
        self.data['groups'].append({
            'group': group,
            'level': 0,
            'permissions': permissions
            }) #now in the instance

You can then use your class:

path_json = r'C:\data\file.json' #raw string
data = Permissions(path_json) #this now reads when you make the class instance
data.add_permissions(json_path, 'guys', {'can_do_icecream': False, 'can_do_nothing': True})
data.write_permissions(r'C:\data\new_file.json') #raw string

Upvotes: 1

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