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Am I not seeing the Error?

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  Am I not seeing the Error? Devyn Collier Johnson <devyncjohnson@gmail.com> - 2013-08-10 22:19 -0400
    Re: Am I not seeing the Error? John Gordon <gordon@panix.com> - 2013-08-12 14:47 +0000
    Re: Am I not seeing the Error? Denis McMahon <denismfmcmahon@gmail.com> - 2013-08-13 20:28 +0000
      Re: Am I not seeing the Error? Dave Angel <davea@davea.name> - 2013-08-13 21:16 +0000
      Re: Am I not seeing the Error? MRAB <python@mrabarnett.plus.com> - 2013-08-14 00:44 +0100
      Re: Am I not seeing the Error? Ned Batchelder <ned@nedbatchelder.com> - 2013-08-13 20:00 -0400
        Re: Am I not seeing the Error? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-08-14 13:20 +1200
          Re: Am I not seeing the Error? Joshua Landau <joshua@landau.ws> - 2013-08-14 07:59 +0100
          Re: Am I not seeing the Error? Chris Angelico <rosuav@gmail.com> - 2013-08-14 13:07 +0100
            Re: Am I not seeing the Error? Roy Smith <roy@panix.com> - 2013-08-14 08:39 -0400
          Re: Am I not seeing the Error? Joshua Landau <joshua@landau.ws> - 2013-08-14 13:34 +0100

#52343 — Am I not seeing the Error?

I am checking my 1292-line script for syntax errors. I ran the following 
commands in a terminal to check for errors, but I do not see the error.

collier@Nacho-Laptop:/media/collier/AI/Pysh$ python3 -m py_compile 
./beta_engine
   File "./beta_engine", line 344
     JOB_WRITEURGFILES = 
multiprocessing.Process(write2file('./mem/ENGINE_PID', ENGINEPID); 
write2file(SENTEMPPATH, ''); write2file(INPUTMEM, '')); 
JOB_WRITEURGFILES.start()
^
SyntaxError: invalid syntax
collier@Nacho-Laptop:/media/collier/AI/Pysh$ pylint ./beta_engine
No config file found, using default configuration
************* Module beta_engine
E:344,0: invalid syntax


Here is line 344:

JOB_WRITEURGFILES = 
multiprocessing.Process(write2file('./mem/ENGINE_PID', ENGINEPID); 
write2file(SENTEMPPATH, ''); write2file(INPUTMEM, '')); 
JOB_WRITEURGFILES.start()

The ENGINEPID is a variable containing a string. My write2file function is

def write2file(openfile, WRITE):
     with open(openfile, 'rw') as file:
         file.write(WRITE)


Mahalo,

DevynCJohnson@Gmail.com

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#52417

In <mailman.451.1376187574.1251.python-list@python.org> Devyn Collier Johnson <devyncjohnson@gmail.com> writes:

> I am checking my 1292-line script for syntax errors. I ran the following 
> commands in a terminal to check for errors, but I do not see the error.

>    File "./beta_engine", line 344
>      JOB_WRITEURGFILES = 
> multiprocessing.Process(write2file('./mem/ENGINE_PID', ENGINEPID); 

You have too many ('s this line.

> write2file(SENTEMPPATH, ''); write2file(INPUTMEM, '')); 

And too many )'s on this one.

-- 
John Gordon                   A is for Amy, who fell down the stairs
gordon@panix.com              B is for Basil, assaulted by bears
                                -- Edward Gorey, "The Gashlycrumb Tinies"

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#52472

On Sat, 10 Aug 2013 22:19:23 -0400, Devyn Collier Johnson wrote:

> I am checking my 1292-line script for syntax errors. I ran the following
> commands in a terminal to check for errors, but I do not see the error.

> JOB_WRITEURGFILES =
> multiprocessing.Process(write2file('./mem/ENGINE_PID', ENGINEPID);
> write2file(SENTEMPPATH, ''); write2file(INPUTMEM, ''));
> JOB_WRITEURGFILES.start()

When I expand this out to one item per line, 

JOB_WRITEURGFILES =
	multiprocessing.Process
	(
		write2file
		(
			'./mem/ENGINE_PID'
			,
			ENGINEPID
		)
		;
		write2file
		(
			SENTEMPPATH
			,
			''
		)
		; 
		write2file
		(
			INPUTMEM
			,
			''
		) 
	)
;
JOB_WRITEURGFILES.start()

and I wonder (not being familiar with multiprocessing) if perhaps there 
should have been a third ";" after the third write2file in the job 
definition.

-- 
Denis McMahon, denismfmcmahon@gmail.com

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#52473

Denis McMahon wrote:

> On Sat, 10 Aug 2013 22:19:23 -0400, Devyn Collier Johnson wrote:
>
>> I am checking my 1292-line script for syntax errors. I ran the following
>> commands in a terminal to check for errors, but I do not see the error.
>
>> JOB_WRITEURGFILES =
>> multiprocessing.Process(write2file('./mem/ENGINE_PID', ENGINEPID);
>> write2file(SENTEMPPATH, ''); write2file(INPUTMEM, ''));
>> JOB_WRITEURGFILES.start()
>
> When I expand this out to one item per line, 
>
> JOB_WRITEURGFILES =
> 	multiprocessing.Process
> 	(
> 		write2file
> 		(
> 			'./mem/ENGINE_PID'
> 			,
> 			ENGINEPID
> 		)
> 		;
> 		write2file
> 		(
> 			SENTEMPPATH
> 			,
> 			''
> 		)
> 		; 
> 		write2file
> 		(
> 			INPUTMEM
> 			,
> 			''
> 		) 
> 	)
> ;
> JOB_WRITEURGFILES.start()
>
> and I wonder (not being familiar with multiprocessing) if perhaps there 
> should have been a third ";" after the third write2file in the job 
> definition.
>

The mistake is not that it's missing the 3rd, but that the first two
semicolons  should have been commas. These are parameters to a function
call multiprocessing.Process()

-- 
Signature file not found

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#52482

On 13/08/2013 21:28, Denis McMahon wrote:
> On Sat, 10 Aug 2013 22:19:23 -0400, Devyn Collier Johnson wrote:
>
>> I am checking my 1292-line script for syntax errors. I ran the following
>> commands in a terminal to check for errors, but I do not see the error.
>
>> JOB_WRITEURGFILES =
>> multiprocessing.Process(write2file('./mem/ENGINE_PID', ENGINEPID);
>> write2file(SENTEMPPATH, ''); write2file(INPUTMEM, ''));
>> JOB_WRITEURGFILES.start()
>
> When I expand this out to one item per line,
>
> JOB_WRITEURGFILES =
> 	multiprocessing.Process
> 	(
> 		write2file
> 		(
> 			'./mem/ENGINE_PID'
> 			,
> 			ENGINEPID
> 		)
> 		;
> 		write2file
> 		(
> 			SENTEMPPATH
> 			,
> 			''
> 		)
> 		;
> 		write2file
> 		(
> 			INPUTMEM
> 			,
> 			''
> 		)
> 	)
> ;
> JOB_WRITEURGFILES.start()
>
> and I wonder (not being familiar with multiprocessing) if perhaps there
> should have been a third ";" after the third write2file in the job
> definition.
>
No, there shouldn't be _any_ semicolons.

Basically it should be something like:

     my_process = multiprocessing.Process(target=my_function)
     my_process.start()

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#52483

On 8/13/13 5:16 PM, Dave Angel wrote:
> Denis McMahon wrote:
>
>> On Sat, 10 Aug 2013 22:19:23 -0400, Devyn Collier Johnson wrote:
>>
>>> I am checking my 1292-line script for syntax errors. I ran the following
>>> commands in a terminal to check for errors, but I do not see the error.
>>> JOB_WRITEURGFILES =
>>> multiprocessing.Process(write2file('./mem/ENGINE_PID', ENGINEPID);
>>> write2file(SENTEMPPATH, ''); write2file(INPUTMEM, ''));
>>> JOB_WRITEURGFILES.start()
>> When I expand this out to one item per line,
>>
>> JOB_WRITEURGFILES =
>> 	multiprocessing.Process
>> 	(
>> 		write2file
>> 		(
>> 			'./mem/ENGINE_PID'
>> 			,
>> 			ENGINEPID
>> 		)
>> 		;
>> 		write2file
>> 		(
>> 			SENTEMPPATH
>> 			,
>> 			''
>> 		)
>> 		;
>> 		write2file
>> 		(
>> 			INPUTMEM
>> 			,
>> 			''
>> 		)
>> 	)
>> ;
>> JOB_WRITEURGFILES.start()
>>
>> and I wonder (not being familiar with multiprocessing) if perhaps there
>> should have been a third ";" after the third write2file in the job
>> definition.
>>
> The mistake is not that it's missing the 3rd, but that the first two
> semicolons  should have been commas. These are parameters to a function
> call multiprocessing.Process()
Everyone: this program seems to be a direct and misguided 
transliteration from a bash script.  There are dozens of mis-uses like 
this of multiprocessing.Process(), due to a severe misunderstanding of 
what it does and how it works.

We've tried offering help, and all that's happened is we've been told 
that this strange coding style is easier to read.

--Ned.

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#52486

Ned Batchelder wrote:
> Everyone: this program seems to be a direct and misguided 
> transliteration from a bash script.

Not a particularly well-written bash script, either --
it's full of superfluous uses of 'cat'.

-- 
Greg

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#52499

On 14 August 2013 02:20, Gregory Ewing <greg.ewing@canterbury.ac.nz> wrote:
> Ned Batchelder wrote:
>>
>> Everyone: this program seems to be a direct and misguided transliteration
>> from a bash script.
>
> Not a particularly well-written bash script, either --
> it's full of superfluous uses of 'cat'.

What's wrong with cat? Sure it's superfluous but what makes it *bad*?
Personally I often prefer the pipe "cat x | y" form to "x < y"... or
"< y x".

There seems to be a militant "cat is evil" attitude where I feel it's
just normally just people who want to show others they know more bash
than they do.

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#52510

On Wed, Aug 14, 2013 at 7:59 AM, Joshua Landau <joshua@landau.ws> wrote:
> On 14 August 2013 02:20, Gregory Ewing <greg.ewing@canterbury.ac.nz> wrote:
>> Ned Batchelder wrote:
>>>
>>> Everyone: this program seems to be a direct and misguided transliteration
>>> from a bash script.
>>
>> Not a particularly well-written bash script, either --
>> it's full of superfluous uses of 'cat'.
>
> What's wrong with cat? Sure it's superfluous but what makes it *bad*?
> Personally I often prefer the pipe "cat x | y" form to "x < y"... or
> "< y x".

What's the use of it, in that situation? Why not simply use
redirection? (Though you have the letters backward; "cat y | x" would
be the equivalent of your others. Typo, I assume.) You're forking a
process that achieves nothing, if your cat has just one argument.

Of course, there ARE many good uses for cat. If you give it multiple
arguments, or if you have arguments that modify the output on the way
through (eg "cat -n"), then it's not the same as redirection. And some
programs behave differently if stdout is a tty, so the quickest way to
get the porcelain version of something is to append "|cat" to the
command. Or maybe you need to retrieve something that only root can
read, so you use "sudo cat /x/y/z|somescript". But if you could spell
it "x < y", then why not do so?

ChrisA

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#52512

In article <mailman.573.1376482061.1251.python-list@python.org>,
 Chris Angelico <rosuav@gmail.com> wrote:

> On Wed, Aug 14, 2013 at 7:59 AM, Joshua Landau <joshua@landau.ws> wrote:
> > On 14 August 2013 02:20, Gregory Ewing <greg.ewing@canterbury.ac.nz> wrote:
> >> Ned Batchelder wrote:
> >>>
> >>> Everyone: this program seems to be a direct and misguided transliteration
> >>> from a bash script.
> >>
> >> Not a particularly well-written bash script, either --
> >> it's full of superfluous uses of 'cat'.
> >
> > What's wrong with cat? Sure it's superfluous but what makes it *bad*?
> > Personally I often prefer the pipe "cat x | y" form to "x < y"... or
> > "< y x".
> 
> What's the use of it, in that situation? Why not simply use
> redirection? (Though you have the letters backward; "cat y | x" would
> be the equivalent of your others. Typo, I assume.) You're forking a
> process that achieves nothing, if your cat has just one argument.

This is waaaaayyyy off-topic for a Python discussion, but...

There's two reasons UUOC is a silly issue.  First, it may save human 
effort.  I like to build up long complicated commands and pipelines one 
bit at a time, and look at the intermediate results.  Let's say I'm 
starting with a sed command (abstracted from my current shell history)

$ sed -e 's/.*; iOS/iOS/' -e 's/;.*//' -e 's/\..*//' x

When I want to add the next "-e whatever" to the command, I need to get 
it in front of the "x".  If I had written it as:

$ cat x | sed -e 's/.*; iOS/iOS/' -e 's/;.*//' -e 's/\..*//'

I just have to stick it at the end, which is easier; I just type 
control-p and add what I want.  Or, "!!" and keep typing.  A small 
amount of human convenience (especially when it's mine) is worth a lot 
of wasted CPU time.

Second, in some cases, the extra "cat" process may actually speed up 
overall command execution because it provides additional I/O buffering.  
The cat process will read ahead from the disk file and block only when 
its output pipe buffers are full.  When the sed command is ready to 
process more input, it only has to read from the pipe, not wait for a 
(very slow, by comparison) disk read.  Yeah, I know, modern kernels do 
lots of read-ahead buffing on their own.  This gives you more.

Sure, it costs something to fork/exec another process.  So what?  The 
computer exists to do my bidding, not the other way around.

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#52511

On 14 August 2013 13:07, Chris Angelico <rosuav@gmail.com> wrote:
> On Wed, Aug 14, 2013 at 7:59 AM, Joshua Landau <joshua@landau.ws> wrote:
>>
>> What's wrong with cat? Sure it's superfluous but what makes it *bad*?
>> Personally I often prefer the pipe "cat x | y" form to "x < y"... or
>> "< y x".
>
> What's the use of it, in that situation? Why not simply use
> redirection? (Though you have the letters backward; "cat y | x" would
> be the equivalent of your others. Typo, I assume.) You're forking a
> process that achieves nothing, if your cat has just one argument.
>
> Of course, there ARE many good uses for cat. If you give it multiple
> arguments, or if you have arguments that modify the output on the way
> through (eg "cat -n"), then it's not the same as redirection. And some
> programs behave differently if stdout is a tty, so the quickest way to
> get the porcelain version of something is to append "|cat" to the
> command. Or maybe you need to retrieve something that only root can
> read, so you use "sudo cat /x/y/z|somescript". But if you could spell
> it "x < y", then why not do so?

Because "cat y | x" often reads nicer. It's the whole "input ->
function -> function -> ... -> output" thing.

I especially hate "y < input > output" which reads awfully not matter
where you chuck the spaces. "cat input | y > output" however, is
acceptable.

Honestly I do think Python would do well to get a pipe operator,
because in some circumstances it's just cleaner.

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