| Re: Keyword checking [message #31006] |
Wed, 29 May 2002 09:02 |
R.Bauer
Messages: 1424
Registered: November 1998
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Senior Member |
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Randall Skelton wrote:
Dear Randall,
keyword_set
should only used to test variables to be true or false
arg_present
is used to find out if a parameter is called by reference
this gives true and by value gives false
n_elements
returns the number of elements of a parameter
We have set up a test case in our lessons
I have posted some time ago.
I believe all is clear if you once filled out these forms
regards
Reimar
1)
There are three functions given
FUNCTION test1,minimum=min_val
IF KEYWORD_SET(min_val) THEN RETURN,1 ELSE RETURN,0
END
FUNCTION test2,minimum=min_val
IF ARG_PRESENT(min_val) THEN RETURN,1 ELSE RETURN,0
END
FUNCTION test3,minimum=min_val
IF N_ELEMENTS(min_val) GT 0 THEN RETURN,1 ELSE RETURN,0
END
Fill out the form:
CALL | test1 | test2 |test3
____________________________________________________________ ____
PRINT, testX( ) | | |
____________________________________________________________ ____
PRINT, testX(minimum=0) | | |
____________________________________________________________ ____
PRINT, testX(minimum=10) | | |
____________________________________________________________ ____
PRINT, testX(minimum=-10) | | |
____________________________________________________________ ____
mv=0 & PRINT, testX(minimum=mv) | | |
____________________________________________________________ _____
mv=10 & PRINT, testX(minimum=mv) | | |
____________________________________________________________ _____
PRINT, testX(minimum=mv2) | | |
____________________________________________________________ _____
2)
There are three functions given
FUNCTION test1,min_val
IF KEYWORD_SET(min_val) THEN RETURN,1 ELSE RETURN,0
END
FUNCTION test2,min_val
IF ARG_PRESENT(min_val) THEN RETURN,1 ELSE RETURN,0
END
FUNCTION test3,min_val
IF N_ELEMENTS(min_val) GT 0 THEN RETURN,1 ELSE RETURN,0
END
Fill out the form:
CALL | test1 | test2 |test3
____________________________________________________________ ____
PRINT, testX( ) | | |
____________________________________________________________ ____
PRINT, testX(0) | | |
____________________________________________________________ _____
PRINT, testX(10) | | |
____________________________________________________________ ____
PRINT, testX(-10) | | |
____________________________________________________________ ____
mv=0 & PRINT, testX(mv) | | |
____________________________________________________________ _____
mv=10 & PRINT, testX(mv) | | |
____________________________________________________________ _____
PRINT, testX(mv2) | | |
____________________________________________________________ _____
>
> I have run into a great deal of trouble checking keywords in IDL and I
> thought I would relay my thoughts and frustrations. I am trying to
> prevent a user from passing an undefined variable in a keyword...
>
> Imagine,
>
> pro test, A=a, B=b
> print, n_params()
> print, arg_present(a), keyword_set(a), n_elements(a), size(a,/type)
> print, arg_present(b), keyword_set(b), n_elements(b), size(b,/type)
> end
>
> If I call this routine as:
>
> IDL> .reset
> IDL> test, a=1, b=undefvar
> % Compiled module: TEST.
> 0
> 0 1 1 2
> 1 0 0 0
>
> So, in order to prevent a user from passing junk in a keyword, I have:
>
> pro test, B=b
> if n_elements(b) eq 0 and arg_present(b) eq 1 then $
> message, 'You passed an undefined variable as a keyword'
> if n_elements(b) gt 0 then b = 'passed'
> end
>
> Now,
>
> IDL> .reset
> IDL> test, b=junk
> % Compiled module: TEST.
> % TEST: You passed an undefined variable as a keyword
>
> Surely there must be something simpiler than my 2-step approach ;)
>
> Cheers,
> Randall
--
Reimar Bauer
Institut fuer Stratosphaerische Chemie (ICG-I)
Forschungszentrum Juelich
email: R.Bauer@fz-juelich.de
------------------------------------------------------------ -------
a IDL library at ForschungsZentrum Juelich
http://www.fz-juelich.de/icg/icg1/idl_icglib/idl_lib_intro.h tml
============================================================ =======
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| Re: Keyword checking [message #31007 is a reply to message #31006] |
Wed, 29 May 2002 08:22  |
Liam E. Gumley
Messages: 378
Registered: January 2000
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Senior Member |
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William Thompson wrote:
[stuff deleted]
> I agree. I can't think of any legitimate reason why one would want to generate
> an error message if an undefined keyword was passed.
[stuff deleted]
As David points out, there are ways to do this sort of checking. However
I must agree with William. In my mind, the whole point of keywords is
that they are *optional*. If a valid defined variable is not passed for
a keyword, then the called routine must take some default action. If the
keyword is important enough that the developer thinks argument checking
wizardry is necessary, then perhaps it should be a positional parameter
instead.
Cheers,
Liam.
Practical IDL Programming
http://www.gumley.com/
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| Re: Keyword checking [message #31009 is a reply to message #31007] |
Wed, 29 May 2002 07:55 |
thompson
Messages: 584
Registered: August 1991
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Senior Member |
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Paul van Delst <paul.vandelst@noaa.gov> writes:
> Randall Skelton wrote:
>>
>> I have run into a great deal of trouble checking keywords in IDL and I
>> thought I would relay my thoughts and frustrations. I am trying to
>> prevent a user from passing an undefined variable in a keyword...
>>
(stuff deleted)
> Why the arg_present? Do you specifically want to tell the user that what they
> passed was undefined? I thought arg_present was for using when you wanted to
> return something in the variable? If the data is for input only, won't
> n_elements() suffice?
> me confused.
I agree. I can't think of any legitimate reason why one would want to generate
an error message if an undefined keyword was passed.
In the case of an input keyword, and undefined keyword should be treated
exactly as if the keyword was not passed at all. The reason for this is quite
simple. If one has embedded subroutines with keyword inheritance, there has to
be some way to pass the keywords along. For example
pro test1, key1=key1
test2, key1=key1
return
end
pro test2, key1=key1
if n_elements(key1) ne 0 then help, key1 else print, 'KEY1 not passed'
return
end
This obviously very trivial example is enough to illustrate my point. If the
user calls the procedure TEST1, the keyword KEY1 will be passed along to TEST2
whether or not the user called TEST1 with that keyword. If the user simply
calls TEST1 without the keyword, it will still appear in TEST2 as an undefined
value. There's nothing wrong with that.
In the output case, all one cares about is whether or not there's a variable to
receive the output. It doesn't matter if the variable was defined previously
or not.
I can only conclude that trapping an undefined keyword as an error is bad IDL
programming practice.
William Thompson
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| Re: Keyword checking [message #31011 is a reply to message #31009] |
Wed, 29 May 2002 07:15 |
Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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Randall Skelton wrote:
>
> I have run into a great deal of trouble checking keywords in IDL and I
> thought I would relay my thoughts and frustrations. I am trying to
> prevent a user from passing an undefined variable in a keyword...
>
> Imagine,
>
> pro test, A=a, B=b
> print, n_params()
> print, arg_present(a), keyword_set(a), n_elements(a), size(a,/type)
> print, arg_present(b), keyword_set(b), n_elements(b), size(b,/type)
> end
>
> If I call this routine as:
>
> IDL> .reset
> IDL> test, a=1, b=undefvar
> % Compiled module: TEST.
> 0
> 0 1 1 2
> 1 0 0 0
>
> So, in order to prevent a user from passing junk in a keyword, I have:
>
> pro test, B=b
> if n_elements(b) eq 0 and arg_present(b) eq 1 then $
> message, 'You passed an undefined variable as a keyword'
> if n_elements(b) gt 0 then b = 'passed'
> end
>
> Now,
>
> IDL> .reset
> IDL> test, b=junk
> % Compiled module: TEST.
> % TEST: You passed an undefined variable as a keyword
>
> Surely there must be something simpiler than my 2-step approach ;)
Why the arg_present? Do you specifically want to tell the user that what they passed was
undefined? I thought arg_present was for using when you wanted to return something in the
variable? If the data is for input only, won't n_elements() suffice?
me confused.
paulv
--
Paul van Delst Religious and cultural
CIMSS @ NOAA/NCEP/EMC purity is a fundamentalist
Ph: (301)763-8000 x7274 fantasy
Fax:(301)763-8545 V.S.Naipaul
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| Re: Keyword checking [message #31012 is a reply to message #31011] |
Wed, 29 May 2002 07:04 |
Jaco van Gorkom
Messages: 97
Registered: November 2000
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Member |
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"Jaco van Gorkom" <j.c.van.gorkom@fz-juelich.de> wrote in message
news:ad2mat$3b09$1@zam602.zam.kfa-juelich.de...
> "Randall Skelton" <rhskelto@atm.ox.ac.uk> wrote in message
> news:Pine.LNX.4.33.0205291352100.19744-100000@mulligan.atm.o x.ac.uk...
>>
>> pro test, B=b
>> if n_elements(b) eq 0 and arg_present(b) eq 1 then $
>> message, 'You passed an undefined variable as a keyword'
>> if n_elements(b) gt 0 then b = 'passed'
>> end
>>
>> Surely there must be something simpiler than my 2-step approach ;)
>
> If the difference between "passing nothing" and "not passing anything"
> is really important to you, then this is it :-)
> Of course, you could always write this into your own function
> KEYWORD_UNDEFINED()...
Well, try to, maybe. As I sent this, it occurred to me that arg_present()
works only in the present function, sort of. Still, there may be
undocumented ways?
jaco
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| Re: Keyword checking [message #31013 is a reply to message #31012] |
Wed, 29 May 2002 06:52 |
Jaco van Gorkom
Messages: 97
Registered: November 2000
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Member |
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"Randall Skelton" <rhskelto@atm.ox.ac.uk> wrote in message
news:Pine.LNX.4.33.0205291352100.19744-100000@mulligan.atm.o x.ac.uk...
>
> pro test, B=b
> if n_elements(b) eq 0 and arg_present(b) eq 1 then $
> message, 'You passed an undefined variable as a keyword'
> if n_elements(b) gt 0 then b = 'passed'
> end
>
> Surely there must be something simpiler than my 2-step approach ;)
If the difference between "passing nothing" and "not passing anything"
is really important to you, then this is it :-)
Of course, you could always write this into your own function
KEYWORD_UNDEFINED()...
cheers,
Jaco
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