What happens when an object is set to null?
Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Python's None: Null in Python Show
If you have experience with other programming languages, like C or
Java, then you’ve probably heard of the concept of Python uses the keyword In this tutorial, you’ll learn:
Understanding Null in Python
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When you call In fact, >>>
Interestingly, >>>
It may look strange, but
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Here, Using Python’s Null Object NoneOften, you’ll use
In the code block below, you’re testing if
the pattern >>>
Here, you use
The equality operators can be fooled when you’re comparing user-defined objects that override them: >>>
Here, the equality operator
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The output doesn’t show you that The following objects are all falsy as well:
For more on comparisons, truthy values, and falsy values, you can read about how to use the Python Declaring Null Variables in PythonIn some languages, variables come to life from a declaration. They don’t have to have an initial value assigned to them. In those languages, the initial default value for some types of variables might be >>>
Here, you can see that a variable with the value Using None as a Default ParameterVery often, you’ll use
>>>
Here, you add But if you call this function a couple times with no >>>
The default value for The right way to build this function is to use >>>
Using None as a Null Value in PythonWhat do you do when >>>
Here, the class You can use this technique when >>>
Here you’ve defined a custom class Deciphering None in TracebacksWhen For instance, you
called >>>
Here, your code raises the very common When you see a traceback like this in your code, look for the attribute that raised the error first. Here, it’s Checking for Null in PythonThere are two type checking cases where you’ll care about >>>
This case is similar to when you have no The second case is a bit more challenging. It’s where you’re taking or returning a value that might be The process is similar for parameters:
You modify Taking a Look Under the HoodIn many other languages, >>>
This line shows that
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Here, you can see
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When
you use Even though Python prints the word
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Even though you try to create a new instance, you still get the existing You can prove that >>>
Here, the fact that If you try to assign to >>>
All the examples above show that you can’t modify You can’t subclass >>>
This traceback shows that the interpreter won’t let you make a new class that inherits from Conclusion
Now you can:
How do you use the Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Python's None: Null in Python What does a null object do?The null object lets us connect one layer to another layer. And this allows things to move around a bit.
What happens when an object is assigned null in Java?NullPointerException is thrown in Java when you point to an object with a null value. Java programmers usually encounter this infamous pointer exception when they forget to initialize a variable (because null is the default value for uninitialized reference variables).
Can you set an object to null in Java?In Java, a null value can be assigned to an object reference of any type to indicate that it points to nothing. The compiler assigns null to any uninitialized static and instance members of reference type.
What does it mean if an object variable is null?The null value simply means that the variable does not refer to an object in memory.
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