setdefaultencoding error

[smalltalk]

>>> import sys
>>> sys.setdefaultencoding(utf8)
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
AttributeError: 'module' object has no attribute 'setdefaultencoding'

but i find the attribute"setdefaultencoding" in python manuals

where is the error?