Pythonni mustaqil

None ekanlikka tekshirish
Nonelikka tekshirishning 2 xil metodi mavjud.
Birinchi metodi – is kalit so‘zi yordamida tekshirish.

Ikkinchi metodi esa == yordamida (lekin bu metoddan foydalanish tavsiya etilmaydi, nima uchun ekanligini esa quyida tushuntirishga harakat qilamiz).

Ba’zi misollarni ko‘rib chiqaylik:

null_variable = None
not_null_variable = 'Hammaga salom!'
# is kalit so'zi
if null_variable is None:
print('null_variable is None')
else:
print('null_variable is not None')
if not_null_variable is None:
print('not_null_variable is None')
else:
print('not_null_variable is not None')
# == operatori
if null_variable == None:
print('null_variable is None')
else:
print('null_variable is not None')
if not_null_variable == None:
print('not_null_variable is None')
else:
print('not_null_variable is not None')
Bu kod quyidagi natijani chiqaradi:
null_variable is None
not_null_variable is not None
null_variable is None
not_null_variable is not None
Juda yaxshi, demak, ular bir xil ishni bajarishmoqda. Lekin unchalik emas. Tarkibiy tiplar uchun shunday. Lekin foydalanuvchi klasslari bilan ishlaganda, ehtiyot bo‘lish lozim. Python foydalanuv-chi klasslarida solishtirish operatorlarini qaytadan taqsimlash imkoniyatini beradi. Shu tarzda siz quyidagi klasslarni solishtirishingiz mumkin. Masalan, MyObject == MyOtherObject kabi.


class MyClass:
def __eq__(self, my_object):

• 
  Shunchaki True ni qaytaramiz return True
  

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my_class = MyClass()

if my_class is None:
print('my_class bu None, is kalit so\'zini ishlatdik')
else:
print('my_class bu None emas, is kalit so\'zini ishlatdik')
if my_class == None:
print('my_class bu None, == operatorini ishlatdik')
else:
print('my_class bu None emas, == operatorini ishlatdik')
Hamda biroz kutilmagan natijani olamiz:
my_class is not None, using the is keyword
my_class is None, using the == syntax
Juda ham qiziq, shunday emasmi? Aynan shu sababli None ekanligini tekshirishda is dan foydal-anishni tavsiya etamiz.
Bundan tashqari ba’zi klasslar uchun __eq__ metodiga murojaat qilish ko‘proq vaqtni oladi, is esa undan tezroq bajarilganligi uchun ham afzalroq hisoblanadi.

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