[Tutor] Unexpected behavior of +=

[Michael Broe]

I just discovered the following behavior, but can't find any  
documentation about it:

 >>> list = []
 >>> list = list + 'abc'
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
TypeError: can only concatenate list (not "str") to list

but:

 >>> list = []
 >>> list += 'abc'
 >>> list
['a', 'b', 'c']

Is this a special characteristic that has been added to the augmented  
assignment operator +=; or is it an automatic consequence of +=  
assignment being performed'in place'? (Tho I can't see how it could  
be...)

It just seems very un-Pythonesque to be able to successfully  
concatenate objects of different types like this. And it seems very  
inconsistent with standard assignment.

Indeed, the Python Reference Manual, section 6.3.1 states:

"With the exception of assigning to tuples and multiple targets in a  
single statement, the assignment done by augmented assignment  
statements is handled the same way as normal assignments. Similarly,  
with the exception of the possible in-place behavior, the binary  
operation performed by augmented assignment is the same as the normal  
binary operations."

...which is patently not the case here.

I was scandalized lol!