I was surprised that this assertion fails:

x = 42
x = lambda: x
assert x() == 42

It seems that x ends up recursively referring to itself, so that x(), x()(), etc. are all functions.

What is the rule used to parse this, and where is this documented?

By the way (not unexpectedly given the above), the original value of x has no references left after the lambda definition:

class X:
  def __del__(self): print('deleting')

x = X()
x = lambda: x  # 'deleting' is printed here