all Python 3weakreffunction

weakref.proxy()

weak references

Creates a proxy — a weak reference you use as if it were the object itself, without calling r(). Once the object is gone, any use raises ReferenceError.

Syntax

p = weakref.proxy(obj, callback=None)

A proxy is handier than ref but riskier: ref honestly returns None, while a proxy fails in the middle of an expression with ReferenceError. A proxy is unhashable, so it cannot be a dict key or a set element, and proxy is obj is always False. A callable object yields a CallableProxyType, anything else a ProxyType. If you need to check whether it is still alive, use weakref.ref.

Examples

import weakref
class User:
    name = 'Ann'
u = User()
p = weakref.proxy(u)
print(p.name)  # → Ann
del u
try:
    p.name
except ReferenceError:
    print('ReferenceError')  # → ReferenceError

See also

Common errors

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