Examples of how `str(x)` differs from `x.__str__()`

magic_method_lookup.py

"""
Examples of how `str(x)` differs from x.__str__`()

This behavior is documented here: https://docs.python.org/3.11/reference/datamodel.html#special-lookup
The reason for this is performance, so `x + y` can avoid a dictionary lookup and/or `__getattribute__` call
"""

def override_str(*args):
  return "bar"

class MagicBehavior:
  def __str__(self):
    return "foo"

  def __getattribute__(self, name):
    if name in ("__str__"):
        return override_str
    else:
      raise NotImplementedError # fallback to standard lookup

print(MagicBehavior().__str__()) # prints 'bar', not 'foo'
print(str(MagicBehavior())) # prints 'foo', not 'bar'

class InstanceOverride:
  def __str__(self):
    return "foo"

instance = InstanceOverride()
instance.__str__ = override_str
print(instance.__str__()) # prints 'bar' not 'foo' 
print(str(instance)) # prints 'foo' not 'bar'