Path: csiph.com!usenet.pasdenom.info!gegeweb.org!aioe.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed3.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.001 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'definitions': 0.07; 'namespace': 0.09; 'prevents': 0.09; 'subject:skip:c 10': 0.09; 'cc:addr:python-list': 0.11; 'python': 0.11; 'def': 0.12; 'jan': 0.12; 'comp': 0.16; 'easier.': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'iterator': 0.16; 'leakage': 0.16; 'namespace,': 0.16; 'nesting': 0.16; 'personally,': 0.16; 'scope.': 0.16; 'subject:class': 0.16; 'subject:fails': 0.16; 'weird': 0.16; 'wrote:': 0.18; 'bit': 0.19; '>>>': 0.22; 'hack': 0.22; 'cc:addr:python.org': 0.22; 'print': 0.22; 'cc:2**0': 0.24; 'defined': 0.27; 'header:In-Reply-To:1': 0.27; 'function': 0.29; 'am,': 0.29; "doesn't": 0.30; 'subject:list': 0.30; 'message- id:@mail.gmail.com': 0.30; '"",': 0.31; '13,': 0.31; 'prints': 0.31; 'file': 0.32; 'class': 0.32; 'received:google.com': 0.35; 'keyword': 0.36; 'list': 0.37; 'fact': 0.38; 'that,': 0.38; 'john': 0.61; 'name': 0.63; 'special': 0.74; '2015': 0.84; '7:25': 0.84; 'to:none': 0.92 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:cc :content-type; bh=YMYgYtp6yBxfNnYKll/o6AqwszjHZlS9fRvFHMmKgwY=; b=0hp5kkngihAbkBcNjGAY0FjEHIrLC01vS0L3C0OYx9NkpBEdzIlTrSVqa3arcOgDT4 WT66PoWMKxSKUM3jCmSg4fMxmVeOS2wdOWH2dmGV2u3Q7+99zpuE+kLQ+DAHCu1YQh8K yzjMMSALR7zphC6rbPWeO8J9t7bxyqtzedvPTqb1CtrOnNgdbcx57jZGqr9rq+UlZGyW NYACkV6sORSlzN0BwH8gv3RFYw4+jV4ryp35belK68UAm7RE1HV1FJKTTXKdboJlRaB7 Y5zChCpacPaSMV/nR6tofZH2zkYsZ6ky/bZ8rGcJCcVmzE8et9K/vK7tHzleYzORWhd7 MH8g== MIME-Version: 1.0 X-Received: by 10.50.62.104 with SMTP id x8mr8610089igr.2.1421095883312; Mon, 12 Jan 2015 12:51:23 -0800 (PST) In-Reply-To: References: Date: Tue, 13 Jan 2015 07:51:23 +1100 Subject: Re: Namespace puzzle, list comprehension fails within class definition From: Chris Angelico Cc: "python-list@python.org" Content-Type: text/plain; charset=UTF-8 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 31 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1421095890 news.xs4all.nl 2920 [2001:888:2000:d::a6]:35037 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:83632 On Tue, Jan 13, 2015 at 7:25 AM, John Ladasky wrote: > When I am working inside the class namespace, the print function call on line 8 recognizes the name f and prints the dictionary bound to that name. > > However, the LIST COMPREHENSION defined inside the class namespace generates a NameError. A list comp is defined with a function call: >>> def f(): ... return [x*x for x in range(4)] ... >>> dis.dis(f) 2 0 LOAD_CONST 1 ( at 0x7fdf25981420, file "", line 2>) 3 LOAD_CONST 2 ('f..') 6 MAKE_FUNCTION 0 9 LOAD_GLOBAL 0 (range) 12 LOAD_CONST 3 (4) 15 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 18 GET_ITER 19 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 22 RETURN_VALUE This prevents leakage of the iterator into the enclosing scope. Personally, I think it's a hack to get around the fact that Python doesn't have any concept of sub-function-scope (similar to the weird hack in try/except); if it weren't for that, true nesting would be easier. As it is, function definitions in class scope have a special meaning, and that interferes a bit with list comps. ChrisA