TypeError: can only concatenate list (not "tuple") to list

David Williams david at bibliolabs.com
Mon Jan 4 09:24:56 CET 2010


> Is there any reason for this error? Apart from "nobody cared to write the
> code"
>
> py> [1,2,3] + (4,5)
> Traceback (most recent call last):
>      File "<stdin>", line 1, in <module>
> TypeError: can only concatenate list (not "tuple") to list
>
> In-place addition += does work:
>
> py> a = [1,2,3]
> py> a += (4,5)
> py> a
> [1, 2, 3, 4, 5]
>
> --
> Gabriel Genellina
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>


I guess to expand a bit more on what I said...  What should the result be?
 A list or a tuple?  The reason += works is because the end result is
clear; a list.  But it is ambiguous in the case of concatenation: did you
want a tuple or a list?



More information about the Python-list mailing list