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Python оператор is null

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  1. None (null), или немного о типе NoneType
  2. Эквивалент null в Python: None
  3. Проверка на None
  4. Use try/except
  5. Use the non-equal operator
  6. Summary
  7. How to check for null in Python
  8. How to check if a variable is NULL in Python?
  9. Using the is operator to check if a variable is NULL in Python.
  10. Using the if condition to check if a variable is NULL in Python.
  11. Using the not equal to operator to check if a variable is NULL in Python.
  12. Was this post helpful?
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None (null), или немного о типе NoneType

Python 3 логотип

Ключевое слово null обычно используется во многих языках программирования, таких как Java, C++, C# и JavaScript. Это значение, которое присваивается переменной.

Концепция ключевого слова null в том, что она дает переменной нейтральное или «нулевое» поведение.

Эквивалент null в Python: None

Он был разработан таким образом, по двум причинам:

Многие утверждают, что слово null несколько эзотерично. Это не наиболее дружелюбное слово для новичков. Кроме того, None относится именно к требуемой функциональности — это ничего, и не имеет поведения.

Читайте также:  Python script sys argv

Присвоить переменной значение None очень просто:

Существует много случаев, когда следует использовать None.

Часто вы хотите выполнить действие, которое может работать либо завершиться неудачно. Используя None, вы можете проверить успех действия. Вот пример:

    Python является объектно-ориентированным, и поэтому None - тоже объект, и имеет свой тип.

Проверка на None

Есть (формально) два способа проверить, на равенство None.

Один из способов — с помощью ключевого слова is.

Второй — с помощью == (но никогда не пользуйтесь вторым способом, и я попробую объяснить, почему).

Отлично, так они делают одно и то же! Однако, не совсем. Для встроенных типов - да. Но с пользовательскими классами вы должны быть осторожны. Python предоставляет возможность переопределения операторов сравнения в пользовательских классах. Таким образом, вы можете сравнить классы, например, MyObject == MyOtherObject.
 И получаем немного неожиданный результат:
Интересно, не правда ли? Вот поэтому нужно проверять на None с помощью ключевого слова is.

А ещё (для некоторых классов) вызов метода __eq__ может занимать много времени, и is будет просто-напросто быстрее.

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How To Check If A Variable Is Null In Python

Check if a variable is Null in Python

To check if a variable is Null in Python, there are some methods we have effectively tested: the is operator, Use try/except and the non-equal operator. Follow the article to better understand.

None and Null in Python

Nowaday, the keyword null is used in many programming languages to represent that the pointer is not pointing to any value. NULL is equivalent to 0. A newly created pointer points “miscellaneous” to a particular memory area. Assign the pointer to NULL to make sure it points to 0. Even though 0 is an invalid location, it’s easier to manage than when the pointer points to an area we don’t know.

In Python, there is no null but None .

None is a specific object indicating that the object is missing the presence of a value. The Python Null object is the singleton None .

In other words None in Python is similar to the Null keyword in other programming languages.

Check if a variable is Null in Python

Use the ‘is’ operator

The is operator is used to compare the memory addresses of two arguments. Everything in Python is an object, and each object has its memory address. The is operator checks if two variables refer to the same object in memory.

myVar = None # Check variable myVar is Null if myVar is None: print('The value of the variable myVar is None (null)')
The value of the variable myVar is None (null)

In the above example, I declared value = None and then used the is operator to check if value has None or not. If value is valid, then execute the if statement; otherwise execute the else statement.

Do not use the == operator to check for the value None . Because in some cases will lead to erroneous results.

Use try/except

Use try/except block to check if the variable is None .

The ‘if’ statement in ‘try’ to check variable ‘value’ exists and the value of ‘value’ is ‘none’

try: if myVar is None: print('The value of the variable myVar is None (null)') # Check name exists except NameError: print("The variable myVar does not exist")
The variable myVar does not exist

Use the non-equal operator

Another method to check if a variable is None is using the non-equal or != operator.

myVar = 1 if myVar != None: print('The variable is not null')

Summary

Here are ways to help you check if a variable is Null in Python. Or, if you have any questions about this topic, leave a comment below. I will answer your questions.

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My name is Jason Wilson, you can call me Jason. My major is information technology, and I am proficient in C++, Python, and Java. I hope my writings are useful to you while you study programming languages.

Name of the university: HHAU
Major: IT
Programming Languages: C++, Python, Java

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How to check for null in Python

Python check for null

This article demonstrates the different ways available to check if a variable is NULL in Python.

What is the NULL keyword?

The NULL keyword is a fundamental part of programming. Being used in all popular programming languages like C, C++, or Java, it can essentially be represented as a pointer that points to nothing, or it simply ascertains the fact that the given variable is vacant.

What is NULL in Python?

Python operates differently from the other popular programming languages. Python defines the NULL object with the None keyword instead. These NULL objects are not valued as 0 in Python though. It does not hold any value whatsoever. This None keyword in Python is both an object and a None type data type.

How to check if a variable is NULL in Python?

Using the is operator to check if a variable is NULL in Python.

We can simply use the is operator or the = operator to check if a variable is None in Python.

The following code uses the is operator to check if a variable is NULL in Python.

The above code provides the following output:

We have made use of the is operator in this code to check the condition. Alternatively, we can also make use of the == operator to complete this task.

The following code implements the same by utilizing the == operator.

The above code provides the following output:

Using the if condition to check if a variable is NULL in Python.

We can simply use the if condition along with no additional operators in order to find out whether the given variable is None or not.

The following code uses the if condition to check if a variable is NULL in Python.

The above code provides the following output:

Using the not equal to operator to check if a variable is NULL in Python.

Another method to reveal whether a variable is None or not in Python is to utilize the != or the not equal to operator.

The following code uses the not equal to operator to check if a variable is NULL in Python.

The above code provides the following output:

These are the three methods that can be utilized to check whether the given variable is a None object or not.

Further, we can even check if the given variable is of the None data type as follows.

That’s all about how to check for null in Python.

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