@property is a decorator in Python that disguises the methods of a class as properties. It supports getter, setter, and deleter operations. ① @property makes the method called like a property, improving encapsulation; ② Supports logic such as input verification, delayed calculation; ③ Controls assignment and deletion behavior through @xxx.setter and @xxx.deleter; ④ is often used for data verification, dynamic property generation and existing code compatibility transition; ⑤ When using it, you should pay attention to naming conflicts, inheritance issues and performance impact.
Use @property decorator in Python mainly to handle class property access and assignment more elegantly. It allows methods to be called like properties, while also retaining the benefits of encapsulation, such as validation input or delayed calculations.
What is @property
@property is a built-in decorator used to "disguise" methods in classes as properties. The advantage of this is that you can control the read, set and delete behavior of properties, without external users needing to know the logic behind it.
Let's give the simplest example:
class Circle:
def __init__(self, radius):
self._radius = radius
@property
def radius(self):
return self._radius
@radius.setter
def radius(self, value):
if value <= 0:
raise ValueError("radius must be greater than 0")
self._radius = value In this example, radius seems to be a normal property, but there is actually a check logic behind it. You cannot give negative numbers casually, otherwise exceptions will be thrown.
How to use getter, setter and deleter
@property 's core is three parts: getter, setter and deleter. You can choose whether to implement them as needed.
- Getter : Responsible for returning attribute values
- Setter : Responsible for setting new values, usually including verification logic
- Deleter (less used) : Responsible for deleting attributes, generally used to clean up resources or states
The basic structure is as follows:
class Example:
def __init__(self, value):
self._value = value
@property
def value(self):
return self._value
@value.setter
def value(self, new_value):
self._value = new_value
@value.deleter
def value(self):
del self._valueA few suggestions:
- If you don't write
@value.setter, then this property will only be read - Be careful when using deleter, it may throw subsequent access errors
- The name is
_unified, such as underlined internal variables_
Practical application scenarios
- Data Verification
- For example, when the user enters age, email format, etc.
- Dynamic attribute generation
- It does not actually store the value, but is calculated based on other attributes
- Compatibility transition
- The existing code uses the public attribute. Later, when you want to add logic but don't want to destroy the interface, you can use property to wrap it.
For example:
class Temperature:
def __init__(self, celsius=0):
self._celsius = celsius
@property
def celsius(self):
return self._celsius
@celsius.setter
def celsius(self, value):
if value < -273.15:
raise ValueError("Temperature cannot be lower than absolute zero")
self._celsius = value
@property
def fahrenheit(self):
return (self._celsius * 9/5) 32 Here, fahrenheit is a "virtual attribute" that does not save data, but is only used for conversion.
Notes and FAQs
- Don't overuse : Not every property requires property, only when it really requires control of access.
- Avoid naming conflicts : Don't get confused with property names and private variable names
- Note during inheritance : subclass rewrite property needs to be careful to overwrite getter/setter
- Small performance impact : generally can be ignored unless frequently accessed in high-frequency loops
If you see an error like the following:
can't set attribute
That is most likely because you forgot to add @xxx.setter , or the attribute name conflicts with the internal variable.
Basically that's it. Using @property well can make the class interface cleaner, safer, and easier to maintain.
The above is the detailed content of How to use `@property` in python class. For more information, please follow other related articles on the PHP Chinese website!
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