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I just learned python @ decorator, it's cool, but soon I found my modified code coming out weird problems.
def with_wrapper(param1):
 def dummy_wrapper(fn):
 print param1
 param1 = 'new'
 fn(param1)
 return dummy_wrapper
def dummy():
 @with_wrapper('param1')
 def implementation(param2):
 print param2
dummy()
I debug it, it throws out exception at print param1
UnboundLocalError: local variable 'param1' referenced before assignment
If I remove param1 = 'new' this line, without any modify operation(link to new object) on variables from outer scope, this routine might working.
Is it meaning I only have made one copy of outer scope variables, then make modification?
The policy of variable scope towards decorator is different?

When you assign a value to param1 it becomes a local variable, thus the error. You should ask for help on your scoping questions from the python-tutor list or the general python-list.