Descriptor

Pemrograman Berorientasi Objek Tingkat Menengah di Python

Jake Roach

Data Engineer

Mengubah interaksi dengan atribut

class Student:
    def __init__(self, name, ssn):
        self.name = name
        self.ssn = ssn

# Buat objek student, lalu akses atribut "ssn"
shaw = Student("Daniel Shaw", "193-80-1821")
print(shaw.ssn)

# Jika nilainya diubah atau dihapus, bagaimana menanganinya?

193-80-1821

Membuat descriptor dengan @property

Descriptor adalah objek untuk mengatur cara atribut diambil, diatur, atau dihapus

Buat descriptor dengan @property

"getter", "setter", "deleter"
Nama metode == nama atribut

Descriptor juga dapat dibuat dengan...

Fungsi property()
__get__(), __set__(), __delete__()

class Student:
    def __init__(self, name, ssn):
        self.name = name
        self.ssn = ssn

    @property  
    def ssn(self):
        return "XXX-XX-" + self._ssn[-4:]

    @ssn.setter  
    def ssn(self, new_ssn):
        self._ssn = new_ssn 

    @ssn.deleter
    def ssn(self):
        raise AttributeError("Can't delete SSN")

@property

class Student:
    def __init__(self, name, ssn):
        self.name = name
        self.ssn = ssn  # Does not need to include an underscore

    @property  
    def ssn(self):  # This is the "getter" method
        return "XXX-XX-" + self._ssn[-4:]

Mengontrol cara ssn diambil
Gunakan self._ssn, bukan self.ssn

@ssn.setter

class Student:
    def __init__(self, name, ssn):
        self.name = name
        self.ssn = ssn
    ...

    @ssn.setter  
    def ssn(self, new_ssn):
        if len(new_ssn) == 11:
          # Add things such as data 
          # validation, operations on
          # other attributes, etc.
          self._ssn = new_ssn

@<attribute-name>.setter

Metode "setter" untuk ssn
Validasi kualitas data
Lakukan operasi pada atribut lain

Ingat: gunakan self._ssn, bukan self.ssn!

@ssn.deleter

class Student:
    def __init__(self, name, ssn):
        self.name = name
        self.ssn = ssn

    ...

    @ssn.deleter
    def ssn(self):
        # Can perform clean up, soft delete, raise exception
        raise AttributeError("Can't delete SSN")

Descriptor dalam praktik

shaw = Student("Daniel Shaw", "193-80-1821")
print(shaw.ssn)  # Access the ssn attribute

XXX-XX-1821

shaw.ssn = "821-11-9380"  # Update Shaw's social security number
print(shaw.ssn)

XXX-XX-9380

del shaw.ssn  # Attempt to delete the ssn attribute

AttributeError: Can't delete SSN

Ayo berlatih!

Pemrograman Berorientasi Objek Tingkat Menengah di Python