Python: "name ascii() is not defined"

I've executed this from the Python REPL:

>>> ascii('Łukasz')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'ascii' is not defined
>>> 

Why isn't a built-in function recognized?

The same thing happen when I executed this script with Python interpreter:

#!/user/bin/python
# -*- coding: UTF-8 -*-

def escape_unicode(f):
    def wrap(*args, **kwargs):
        x = f(*args, **kwargs)
        return ascii(x)

    return wrap     

@escape_unicode
def my_name():
    return 'Łukasz'

my_name()

NameError: global name 'ascii' is not defined