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Sun, 22 Nov 2020 23:00:05 -0500 (EST) Received: by tarpaulin.shahaf.local2 (Postfix, from userid 1005) id 4CfYMR5CYlz3kK; Mon, 23 Nov 2020 04:00:03 +0000 (UTC) Date: Mon, 23 Nov 2020 04:00:03 +0000 From: Daniel Shahaf To: Felipe Contreras Cc: Roman Perepelitsa , Zsh hackers list Subject: Re: Bug with unset variables Message-ID: <20201123040003.GB9114@tarpaulin.shahaf.local2> References: <20201118224532.769efe4d@tarpaulin.shahaf.local2> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Seq: 47598 Archived-At: X-Loop: zsh-workers@zsh.org Errors-To: zsh-workers-owner@zsh.org Precedence: list Precedence: bulk Sender: zsh-workers-request@zsh.org X-no-archive: yes List-Id: List-Help: List-Subscribe: List-Unsubscribe: List-Post: List-Owner: List-Archive: Archived-At: Felipe Contreras wrote on Sat, Nov 21, 2020 at 19:20:56 -0600: > On Wed, Nov 18, 2020 at 4:45 PM Daniel Shahaf wrote: > > > Do not argue about a person. Argue about the technical matter at hand. > > That's what I did. The technical matter was being ignored. > > > What are A and B? > > I already explained this multiple times: > > A: unset foo > B: foo = nil And in Python, A is «del foo»; B is «foo = None»; and they aren't equivalent. Actually, more precisely, Python doesn't even *have* a B, because Python doesn't have a syntax for declaring a variable without a value. (When you write «foo = None», that «None» is not implicitly provided by the language.) However, I don't see how any of this is an argument in favour of the behaviour change you proposed. Other languages' behaviours be what they may, they're unlikely to be a good enough reason to break backwards compatibility. (For instance, I don't think a proposal to disable null elision would be accepted, due to backwards compatibility concerns, regardless of how few other languages do null elision.) > > Why does the Python example not use «del» as the "unset" operation? > > Because it doesn't do the same thing as unset. > > In shell, this leaves foo declared in a local scope: > > local foo # declare > unset foo # unset > > In Python, this doesn't: > > foo = None # declare > del foo # undeclare > > They are *not* functionally the same thing. In Python, the "declare" operation would be just «pass», or more precisely, the removal of any «global foo» declarations… but, again, unless this Python discussion somehow bears on a proposed change to zsh, I'm not interested in continuing it.