On 13 October 2012 10:03, Chris Angelico <ros...@gmail.com> wrote: > On Sat, Oct 13, 2012 at 7:41 PM, Thomas Bach > <thb...@students.uni-mainz.de> wrote: > > On Sat, Oct 13, 2012 at 12:32:41AM +0000, Steven D'Aprano wrote: > >> > >> He gets SyntaxError because you can't follow a semicolon with a > >> statement that begins a block. > > > > Can someone provide a link on where to find this type of information? > > I was just hunting through “The Python Language Reference” and could > > not find anything explicit. The only thing I found is > > > > http://docs.python.org/reference/simple_stmts.html > > > > “Several simple statements may occur on a single line separated by > > semicolons.” > > > > Anyways, this does not explicitly say “You shall not put a compound > > statement after a simple statement separated by a semicolon.”, right? > > It's more that Python treats simple and compound statements as > completely separate beasts. You can combine simple statements on one > line, but compound statements mustn't be. > > In my opinion, this is a major wart in Python syntax. You can argue > all you like about how it reduces code clarity to put these sorts of > things together, but that's a job for a style guide, NOT a language > requirement. Most code won't put an assignment followed by an > if/while/for, but when I'm working interactively, I often want to > recall an entire statement to edit and reuse, complete with its > initialization - something like (contrived example): > > >>> a=collections.defaultdict(int) > >>> for x in open("RilvierRex.txt"): a[x]+=1 > > Then I keep doing stuff, keep doing stuff, and then come back to this > pair of lines. Since they're two lines, I have to recall them as two > separate entities, rather than as an initializer and the code that > uses it. Logically, they go together. Logically, they're on par with a > list comprehension, which initializes, loops, and assigns, all as a > single statement. But syntactically, they're two statements that have > to go on separate lines. > > To force that sort of thing to be a single recallable statement, I can > do stupid tricks like: > > >>> if True: > a=collections.defaultdict(int) > for x in open("RilvierRex.txt"): a[x]+=1 > > but that only works in IDLE, not in command-line interactive Python. > > Note, by the way, that it's fine to put the statement _inside_ the for > on the same line. It's even legal to have multiple such statements: > > >>> for x in (1,2,3): print(x); print(x); > 1 > 1 > 2 > 2 > 3 > 3 > > If there's any ambiguity, it would surely be that, and not the simple > statement being first. > > Okay, rant over. I'll go back to being nice now. :)
This here isn't a flaw in Python, though. It's a flaw in the command-line interpreter. By putting it all on one line, you are effectively saying: "group these". Which is the same as an "if True:" block, and some things like Reinteract even supply a grouping block like "build". That said, because some shells suck it would be nice if: > python -c "a=1\nif a:print(a)" worked (just for -c).
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