You are omitting the self parameter which is present in the undecorated function (createHeader in your case).
def formatHeader(fn):
from functools import wraps
@wraps(fn)
def wrapper(self):
return '<div class="page_header">'+fn(self)+'</div>'
return wrapper
If you are unsure about the signature of the function you want to decorate, you can make it rather general as follows:
def formatHeader(fn):
from functools import wraps
@wraps(fn)
def wrapper(*args, **kw):
return '<div class="page_header">'+fn(*args, **kw)+'</div>'
return wrapper