On Fri, Feb 21, 2014 at 7:07 PM, Victor Stinner <victor.stin...@gmail.com> wrote: >> Consider this example of a two-level cache:: >> for key in sequence: >> x = (lvl1[key] except KeyError: (lvl2[key] except KeyError: f(key))) >> # do something with x > > ... but I don't like when it is used to build complex expressions.
This is true of any expression syntax, not just this proposal--though some expression syntax is more apt to be abused than others: you won't see many multiline int literals! ;) > > At the first read, I'm unable to understand this long expression. At > the second read, I'm still unable to see which instruction will be > executed first: lvl1[key] or lvl2[key]? > > The advantage of the current syntax is that the control flow is > obvious, from the top to the bottom: > > # start > try: > x = lvl1[key] # first instruction > except KeyError: > try: > x = lvl2[key] > except KeyError: > x = f(key) # latest instruction > # end > > Thanks to Python indentation, it's easier to see the control flow. > > After having read a lot of code last 10 years, I now try to follow > this rule: one instruction per line. +1 > > For example, I don't like "if ((res = func()) == NULL)" in the C > language, I always split it into two lines. A drawback of writing more > than one instruction is that it's hard to debug instruction per > instruction (in pdb/gdb). Think for example of "if ((res = func()) == > NULL)": if you execute step by step, how do you know which instruction > is currently executed? So true. > > You should maybe write your example differently: > > x = (lvl1[key] > except KeyError: (lvl2[key] > except KeyError: f(key))) > > It looks like the classic try/except syntax. +1 -eric _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
