diff options
Diffstat (limited to 'Doc')
| -rw-r--r-- | Doc/faq/programming.rst | 13 |
1 files changed, 8 insertions, 5 deletions
diff --git a/Doc/faq/programming.rst b/Doc/faq/programming.rst index 7713450..6a720d1 100644 --- a/Doc/faq/programming.rst +++ b/Doc/faq/programming.rst @@ -1131,7 +1131,7 @@ a tuple points to. Under the covers, what this augmented assignment statement is doing is approximately this:: - >>> result = a_tuple[0].__iadd__(1) + >>> result = a_tuple[0] + 1 >>> a_tuple[0] = result Traceback (most recent call last): ... @@ -1154,16 +1154,19 @@ that even though there was an error, the append worked:: >>> a_tuple[0] ['foo', 'item'] -To see why this happens, you need to know that for lists, ``__iadd__`` is equivalent -to calling ``extend`` on the list and returning the list. That's why we say -that for lists, ``+=`` is a "shorthand" for ``list.extend``:: +To see why this happens, you need to know that (a) if an object implements an +``__iadd__`` magic method, it gets called when the ``+=`` augmented assignment +is executed, and its return value is what gets used in the assignment statement; +and (b) for lists, ``__iadd__`` is equivalent to calling ``extend`` on the list +and returning the list. That's why we say that for lists, ``+=`` is a +"shorthand" for ``list.extend``:: >>> a_list = [] >>> a_list += [1] >>> a_list [1] -is equivalent to:: +This is equivalent to:: >>> result = a_list.__iadd__([1]) >>> a_list = result |