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TypeError expected in an augmented assignment

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An hybrid list-tuple concatenation is not allowed

>>> []+(1, 2)
Traceback (most recent call last):                                                                        
  File "<stdin>", line 1, in <module>                                                                     
TypeError: can only concatenate list (not "tuple") to list                                                
>>>  



hence I was expecting (*) that the following code raises a TypeError :

>>> x = []                                                                                                
>>> x += (1, 2)                                                                                           
>>> x                                                                                                     
[1, 2]                                                                                                    
>>>


Any explanation ?


(*) as the docs states, the augmented assignment is supposed to perform the concatenation : 
An augmented assignment (...) performs the binary operation specific to the type of assignment on the two operands (...)

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TypeError expected in an augmented assignment candide <c.candide@laposte.net> - 2014-07-02 19:39 -0700
  Re: TypeError expected in an augmented assignment Terry Reedy <tjreedy@udel.edu> - 2014-07-02 22:57 -0400
    Re: TypeError expected in an augmented assignment candide <c.candide@laposte.net> - 2014-07-03 00:51 -0700
      Re: TypeError expected in an augmented assignment Chris Angelico <rosuav@gmail.com> - 2014-07-03 18:36 +1000
        Re: TypeError expected in an augmented assignment candide <c.candide@laposte.net> - 2014-07-03 02:35 -0700
          Re: TypeError expected in an augmented assignment Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-07-03 13:43 +0100

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