252 – Nested attribute access exception

When trying to access a nested attribute from the outer object, starting from Python 3.15 you’ll get a helpful error message suggesting a fix.

Consider the classes Outer and Inner:

class Inner:
    def __init__(self, value):
        self.value = value

class Outer:
    def __init__(self, value):
        self.inner = Inner(value)

Objects of type Outer have an attribute inner that is an instance of type Inner that contains an attribute value.

If you try to access the attribute value from an instance of Outer, you get a generic AttributeError exception:

# Python 3.14 and earlier
o = Outer()
print(o.value)

Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    print(o.value)
          ^^^^^^^
AttributeError: 'Outer' object has no attribute 'value'

Starting from Python 3.15, Python suggests the correct nested attribute lookup:

# Python 3.15+
o = Outer()
print(o.value)

Traceback (most recent call last):
  File "<python-input-1>", line 2, in <module>
    print(o.value)
          ^^^^^^^
AttributeError: 'Outer' object has no attribute 'value'. Did you mean '.inner.value' instead of '.value'?