Like @Property, but only evaluated once

cacheprop.py

class cacheprop(object):
  def __init__(self, getter): self.getter = getter
  def __get__(self, shelf, _):
    value = self.getter(shelf)
    shelf.__dict__[self.getter.__name__] = value
    return value
  
class Foo():
  @cacheprop
  def bar(self):
    print('baz')
    return 'bat'

foo = Foo()
print(foo.bar)
# 'baz'
# 'bat'
print(foo.bar)
# 'bat'