capture change of global variable value in python

问题

How do i detect or capture change of value of a global variable in python

variable = 10
print(variable)
variable = 20 
# Detect changes to the value using a signal to trigger a function

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回答1:

To my knowledge, it is not possible to generically capture the assignment of a global symbol in Python (At least in CPython where globals are stored in a dict in the module object, both are C types that cannot be monkey patched).

Here's a simple workaround that's a bit of a compromise. Use a wrapper object to store your monitored variables, and define __setattr__ to do whatever you want to do before (or after) setting an attribute.

class CaptureOnSetAttribute:
    def __setattr__(self, attr, value):
        # our hook to do something
        print(f'set value of {attr} to {value}')
        # actually set the attribute the normal way after
        super().__setattr__(attr, value)


wrapper_object = CaptureOnSetAttribute()

The compromise of course is that now instead of writing something like:

monitored_global = value

You must now write:

wrapper_object.monitored_attribute = value

来源：https://stackoverflow.com/questions/59675250/capture-change-of-global-variable-value-in-python