pymagic9

This is a Python library based on calling the stack of frames at runtime and analyzing the code object of frames. Basically, it implements some C# features. For example, it contains the nameof function and auto-implemented properties. See the documentation for more information.

Installation

You can install pymagic9 using pip:

pip install pymagic9

Features

getframe: The sys._getframe function is used here if it exists in the version of python being used. Otherwise, the _getframe polyfill is used.

isemptyfunction: Checks if a function is empty or not.

isfunctionincallchain: Determines whether the given function object or code object is present in the call chain.

nameof: This function correctly determines the "name" of an object, without being tied to the object itself. It can be used to retrieve the name of variables, functions, classes, modules, and more.

PropertyMeta: This metaclass allows you to create auto-implemented properties (like in C#, where you can declare properties without explicitly defining a getter and setter), for which you can use an ellipsis or empty functions to indicate that the Python itself would create the auto-implemented accessor.

Usage of auto-implemented properties

1. Import the PropertyMeta metaclass and assign it as a metaclass for the desired class:

from pymagic9 import PropertyMeta


class Person(metaclass=PropertyMeta):
    pass

2. Create properties in this class with empty accessors (using empty function or ellipsis) to indicate that this property will be auto-implemented:

from pymagic9 import PropertyMeta


class Person(metaclass=PropertyMeta):
    """class Person"""
    def __init__(self, name):
        self.name = name

    name = property(fget=...,)           # readonly property
    age = property(fget=..., fset=...,)  # ordinary property

3. Now for an ordinary property we can get and put values into it at any time. But for a readonly property, you can put a value into it only once, at the time of creating an instance of the class:

from pymagic9 import PropertyMeta


class Person(metaclass=PropertyMeta):
    """class Person"""
    def __init__(self, name):
        self.name = name
        # self.name = "Sam"  # raise AttributeError: 'property' is readonly (reassigning value)

    name = property(fget=...,)           # readonly property
    age = property(fget=..., fset=...,)  # ordinary property

    
if __name__ == "__main__":
    person = Person("Tom")
    person.age = 24
    print(person.name + ',', person.age)  # Tom, 24
    # person.name = "Sam"  # raise AttributeError: 'property' is readonly

4. To delete a property value, use the del operator:

from pymagic9 import PropertyMeta


class Person(metaclass=PropertyMeta):
    """class Person"""
    def __init__(self, name):
        self.name = name

    name = property(fget=...,)           # readonly property
    age = property(fget=..., fset=...,)  # ordinary property

    
if __name__ == "__main__":
    person = Person("Tom")
    person.age = 24
    print(person.name + ',', person.age)  # Tom, 24
    del person.name
    # print(person.name)  # raise AttributeError: auto-implemented field does not exist or has already been erased

5. If the getter is specified by an empty accessor (using empty function or ellipsis), and the setter is not an empty function, then setter will also be called. This can be used as a callback when assigning a value to a property:

from pymagic9 import nameof, PropertyMeta


def NotifyPropertyChanged(propertyname, value):
    """Notify property changed"""
    # Do something
    print(propertyname + ',', value)


class Person(metaclass=PropertyMeta):
    """class Person"""
    def __init__(self, name):
        self.name = name

    name = property(fget=...,)           # readonly property
    age = property(fget=..., fset=...,)  # ordinary property
    
    @property
    def height(self):
        """Person height in cm"""
        return
    
    @height.setter
    def height(self, value):
        NotifyPropertyChanged(nameof(self.height), value)


if __name__ == "__main__":
    person = Person("Tom")
    person.age = 24
    print(person.name + ',', person.age)  # Tom, 24
    person.height = 180  # height, 180

6. Similar code for Python 2.7 looks like this:

from pymagic9 import nameof, PropertyMeta

__metaclass__ = PropertyMeta


def NotifyPropertyChanged(propertyname, value):
    """Notify property changed"""
    # Do something
    print(propertyname + ', ' + str(value))
    
    
class Person:
    """class Person"""
    def __init__(self, name):
        self.name = name

    name = property(fget=Ellipsis,)                # readonly property
    age = property(fget=Ellipsis, fset=Ellipsis,)  # ordinary property
    
    @property
    def height(self):
        """Person height in cm"""
        return
    
    @height.setter
    def height(self, value):
        NotifyPropertyChanged(nameof(self.height), value)


if __name__ == "__main__":
    person = Person("Tom")
    person.age = 24
    print(person.name + ', ' + str(person.age))  # Tom, 24
    person.height = 180  # height, 180

The detailed operating principle is described in the documentation.

Compatibility

pymagic9 is compatible with the following versions of Python:

• CPython 2.7
• CPython 3.6
• CPython 3.7
• CPython 3.8
• CPython 3.9
• CPython 3.10

It is supported on Windows, Ubuntu, and MacOS platforms.

Documentation

For more information and detailed usage examples, please refer to the documentation.

License

This project is licensed under the Apache License 2.0. See the LICENSE file for more details.