Python での関数のパラメータ受け渡しに関する簡単な説明

>>> def add(a,b): 
  return a+b 
 
>>> print add(1,2) 
3
>>> print add('abc','123') 
abc123

>>> def myjoin(string,sep='_'): 
  return sep.join(string) 
 
>>> myjoin('Test') 
'T_e_s_t'
>>> myjoin('Test',';') 
'T;e;s;t' 
?
>>> def myrange(start=0,stop,step=1): 
  print stop,start,step 
   
SyntaxError: non-default argument follows default argument

>>> def printf(fmt,*arg): 
  print fmt%arg 
 
   
>>> printf ('%d is larger than %d',2,1) 
2 is larger than 1