I can not identify the missing argument

Question

I am trying to write a code to show the list of privileges for the object User1.

class User: def __init__(self, f_name, l_name, age): self.f_name = f_name self.l_name = l_name self.age = age def describe(self): print(f"The user {self.f_name} {self.l_name} has {self.age} years old person.") def greet(self): print(f"Hi {self.f_name}, you are the Administer right now!") class Privileges: def __init__(self, privileges): self.privileges = ['add post', 'del post', 'ban users'] def show_privileges(self): print(f"These are the Admin list of privileges: {self.privileges}.") class Admin(User): def __init__(self, f_name, l_name, age): super().__init__(f_name, l_name, age) self.privileges = Privileges() user1 = Admin('Porco', 'Rosso', 42) user1.privileges.show_privileges()

This is the output but I can not find this missing argument:

 Traceback (most recent call last): File "C:\Users\Administrator\Desktop\python_work\teste34.py", line 25, in <module> user1 = Admin('Porco', 'Rosso', 42) File "C:\Users\Administrator\Desktop\python_work\teste34.py", line 23, in __init__ self.privileges = Privileges() TypeError: __init__() missing 1 required positional argument: 'privileges' [Finished in 0.433s]

I would like to complement with a code I did before where there were no need to pass the argument:

 class User: def __init__(self, f_name, l_name, age): self.f_name = f_name self.l_name = l_name self.age = age def describe(self): print(f"The user {self.f_name} {self.l_name} has {self.age} years old person.") def greet(self): print(f"Hi {self.f_name}, you are now the Admin!") class Admin(User): def __init__(self, f_name, l_name, age): super().__init__(f_name, l_name, age) self.privileges = ['add post', 'del post', 'ban users'] def show_privileges(self): print(f"These are SysOp list of privileges: {self.privileges}.") user1 = Admin('Porco', 'Rosso', 42) user1.describe() user1.greet() user1.show_privileges()

self.privileges = Privileges() you need to pass something in the Privileges(___) or remove privileges from def __init__(self, privileges): — Sayandip Dutta
– Sayandip Dutta, Commented Feb 24, 2020 at 11:38
The error message says it explicitly: "__init__() missing 1 required positional argument: 'privileges' - you're calling Privileges class (and thus its __init__ method) without arguments in class Admin. — Błotosmętek
– Błotosmętek, Commented Feb 24, 2020 at 11:39
@SayandipDutta thanks but I was thinking that the list (self.privileges = ['add post', 'del post', 'ban users'])would be passed automatic. This is the reason to write instantiate a class as a method. No? — Vinicivs
– Vinicivs, Commented Feb 24, 2020 at 11:45

ShadowRanger · Accepted Answer · 2020-02-24 12:02:02Z

 self.privileges = Privileges()

doesn't pass any arguments.

class Privileges: def __init__(self, privileges):

demands an argument named privileges. It never uses it though, so perhaps you just need to remove it, making it:

class Privileges: def __init__(self):

If it's supposed to have a default value, you want something like:

class Privileges: def init(self, privileges=('add post', 'del post', 'ban users')): self.privileges = list(privileges)

Note that you shallow copy whatever you were passed to avoid the problems with mutable default arguments and similar issues if a user passes their own list (where you don't want your modifications to affect them, or vice-versa).

Sayandip Dutta · Accepted Answer · 2020-02-24 11:59:40Z

According your comments, you were meaning to pass the argument in the __init__ of class Priviliges implicitly. In order to do that, you needed a default argument:

class User: def __init__(self, f_name, l_name, age): self.f_name = f_name self.l_name = l_name self.age = age def describe(self): print(f"The user {self.f_name} {self.l_name} has {self.age} years old person.") def greet(self): print(f"Hi {self.f_name}, you are the Administer right now!") class Privileges: def __init__(self, privileges = ['add post', 'del post', 'ban users']): self.privileges = privileges def show_privileges(self): print(f"These are the Admin list of privileges: {self.privileges}.") class Admin(User): def __init__(self, f_name, l_name, age): super().__init__(f_name, l_name, age) self.privileges = Privileges() user1 = Admin('Porco', 'Rosso', 42) user1.privileges.show_privileges()

Output:

These are the Admin list of privileges: ['add post', 'del post', 'ban users'].

NOTE

However, using mutable types as default argument is strongly discouraged.

@ShadowRanger I know, I should add not recommended in the answer body.

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