[Zope] A quick zope/python question
I have a short python script:
gc = context.restrictedTraverse('coup/temp_folder/GarbageCollector', None)
print 'gc=',str(gc)
if gc:
print 'GarbageCollector exists'
else:
print 'No GarbageCollector'
which, when run produces:
gc= TransientObjectContainer at GarbageCollector
No GarbageCollector
Which is really strange because 'gc' was just reported to be a TOC!
When the script is changed to:
gc = context.restrictedTraverse('coup/temp_folder/GarbageCollector', None)
print 'gc=',str(gc)
if gc is not None:
print 'GarbageCollector exists'
else:
print 'No GarbageCollector'
I get the expected response:
gc= TransientObjectContainer at GarbageCollector
GarbageCollector exists
I think I am misunderstanding something basic about python/zope here. Why
does a TOC object evaluate to false?
Thanks,
Jonathan
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Re: [Zope] A quick zope/python question
On 5/9/06, Jonathan [EMAIL PROTECTED] wrote: I think I am misunderstanding something basic about python/zope here. Why does a TOC object evaluate to false? Well, why not? If you are checking for none-ness, use is None. Evaluating the object is wrong. If the TOC object evaluates to something empty as a side-effect of something, or because it explicitly is supposed to return something useful when evaluated, who in this case happens to be empty/false, is besides the point. It should be easy to figure out if you read the source, though. :-) -- Lennart Regebro, Nuxeo http://www.nuxeo.com/ CPS Content Management http://www.cps-project.org/ ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
Re: [Zope] A quick zope/python question
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 9 May 2006, at 16:18, Jonathan wrote: gc= TransientObjectContainer at GarbageCollector GarbageCollector exists I think I am misunderstanding something basic about python/zope here. Why does a TOC object evaluate to false? I think the basic misunderstanding is about what happens if you say... if FOO: ... Python will try to evaluate using steps such as looking for methods like __nonzero__, __len__, etc, and you're not aware what these may evaluate to given your object. A Folder, for example, evaluates to False when it is empty. You should use a different test to determine if that item exists. jens -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.1 (Darwin) iD8DBQFEYLRlRAx5nvEhZLIRAmSWAKCxP+IjWYHEC/J1E8zDvq0R2OUB1wCePA74 Fm8Oc74d3dn915gDefbR1Yo= =FOpK -END PGP SIGNATURE- ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
Re: [Zope] A quick zope/python question
--On 9. Mai 2006 11:18:25 -0400 Jonathan [EMAIL PROTECTED] wrote:
I have a short python script:
gc = context.restrictedTraverse('coup/temp_folder/GarbageCollector', None)
print 'gc=',str(gc)
if gc:
print 'GarbageCollector exists'
else:
print 'No GarbageCollector'
which, when run produces:
Check the implementation. if obj calls obj.__nonzero__() or
obj.__len__().. depending on the implemenation this will explain the result
When the script is changed to:
gc = context.restrictedTraverse('coup/temp_folder/GarbageCollector', None)
print 'gc=',str(gc)
if gc is not None:
print 'GarbageCollector exists'
else:
print 'No GarbageCollector'
This is the right way to do it.
-aj
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pgppDSSxP4hG6.pgp
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Re: [Zope] A quick zope/python question
Thanks to everyone for setting me straight! I have been (erroneously!) assuming that any defined object would evaluate to 'true'. Thanks again. Jonathan - Original Message - From: Jens Vagelpohl [EMAIL PROTECTED] To: [Zope] Mailing List zope@zope.org Sent: Tuesday, May 09, 2006 11:25 AM Subject: Re: [Zope] A quick zope/python question -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 9 May 2006, at 16:18, Jonathan wrote: gc= TransientObjectContainer at GarbageCollector GarbageCollector exists I think I am misunderstanding something basic about python/zope here. Why does a TOC object evaluate to false? I think the basic misunderstanding is about what happens if you say... if FOO: ... Python will try to evaluate using steps such as looking for methods like __nonzero__, __len__, etc, and you're not aware what these may evaluate to given your object. A Folder, for example, evaluates to False when it is empty. You should use a different test to determine if that item exists. jens -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.1 (Darwin) iD8DBQFEYLRlRAx5nvEhZLIRAmSWAKCxP+IjWYHEC/J1E8zDvq0R2OUB1wCePA74 Fm8Oc74d3dn915gDefbR1Yo= =FOpK -END PGP SIGNATURE- ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev ) ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
[Zope] python question
hi all! i think there should be no functional difference in the two code snippets below, but is there any difference in performance? (i know, the except AttributeError could possibly mask an AttributeError in the called function...) 1.: hook = getattr(o, '_before_transaction_commit', None) if hook: hook() 2.: try: o._before_transaction_commit() except AttributeError: pass regards, juergen herrmann ___ XLhost.de - eXperts in Linux hosting Juergen Herrmann Weiherweg 10, 93051 Regensburg, Germany Fon: +49 (0)700 XLHOSTDE [0700 95467833] Fax: +49 (0)721 151 463027 ICQ: 27139974 - IRC: [EMAIL PROTECTED] WEB: http://www.XLhost.de ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
Re: [Zope] python question
--On 1. Juli 2005 17:10:58 +0200 Jürgen Herrmann [EMAIL PROTECTED] wrote: hi all! i think there should be no functional difference in the two code snippets below, but is there any difference in performance? You could benchmark it :-) -aj pgphfg7D56dFp.pgp Description: PGP signature ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
Re: [Zope] python question
On 7/1/05, Jürgen Herrmann [EMAIL PROTECTED] wrote: i think there should be no functional difference in the two code snippets below, but is there any difference in performance? Don't know, and don't care; these are (at the Python level) functionally different. (i know, the except AttributeError could possibly mask an AttributeError in the called function...) Exactly. Shouldn't be a real issue in a released version, but better safe than sorry. 1.: hook = getattr(o, '_before_transaction_commit', None) if hook: hook() Better yet: hook = getattr(o, '_before_transaction_commit', None) if hook is not None: hook() -Fred -- Fred L. Drake, Jr.fdrake at gmail.com Zope Corporation ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
[Zope] python question
I may be asking this in the wrong place but I have a tal page where I want
to use python to display only the most recent addition to a folder of files.
I can sort the folder and return all the files easily with:
return sequence.sort(files, (('bobobase_modification_time', 'cmp',
'desc'),))
How do I return just the most recent one? (I tried sorting and then using
return max(files) but that doesn't give me all the properties and I need
them for display)
Kate
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RE: [Zope] python question
sort() on a sequence does not return anything. It operates on the
[mutable] sequence in place.
You probably want to push this bit into a python script where you have
more elbow room, and do this:
files.sort(etc,etc)
return files[0]
hth,
Jim
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Kate Legere
Sent: Tuesday, May 31, 2005 3:35 PM
To: Zope
Subject: [Zope] python question
I may be asking this in the wrong place but I have a tal page
where I want to use python to display only the most recent
addition to a folder of files.
I can sort the folder and return all the files easily with:
return sequence.sort(files, (('bobobase_modification_time', 'cmp',
'desc'),))
How do I return just the most recent one? (I tried sorting
and then using return max(files) but that doesn't give me all
the properties and I need them for display)
Kate
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Re: [Zope] python question
Kate Legere wrote:
I may be asking this in the wrong place but I have a tal page where I want
to use python to display only the most recent addition to a folder of files.
I can sort the folder and return all the files easily with:
return sequence.sort(files, (('bobobase_modification_time', 'cmp',
'desc'),))
How do I return just the most recent one? (I tried sorting and then using
return max(files) but that doesn't give me all the properties and I need
them for display)
If it's sorted, you can use a Python slice::
return sequence.sort(files, (('bobobase_modification_time',
'cmp', 'desc'),))[0]
The trick is the last three characters. See
http://docs.python.org/tut/node5.html
--jcc
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RE: [Zope] python question
Thanks - turns out the real error was in the file dealing with it - all
fixed now.
Thanks for the help.
Kate
-Original Message-
From: Jim Abramson [mailto:[EMAIL PROTECTED]
Sent: Tuesday, May 31, 2005 2:38 PM
To: Kate Legere; Zope
Subject: RE: [Zope] python question
sort() on a sequence does not return anything. It operates on the
[mutable] sequence in place.
You probably want to push this bit into a python script where you have
more elbow room, and do this:
files.sort(etc,etc)
return files[0]
hth,
Jim
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Kate Legere
Sent: Tuesday, May 31, 2005 3:35 PM
To: Zope
Subject: [Zope] python question
I may be asking this in the wrong place but I have a tal page
where I want to use python to display only the most recent
addition to a folder of files.
I can sort the folder and return all the files easily with:
return sequence.sort(files, (('bobobase_modification_time', 'cmp',
'desc'),))
How do I return just the most recent one? (I tried sorting
and then using return max(files) but that doesn't give me all
the properties and I need them for display)
Kate
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Re: [Zope] python question
Am Dienstag, den 31.05.2005, 15:34 -0400 schrieb Kate Legere:
I may be asking this in the wrong place but I have a tal page where I want
to use python to display only the most recent addition to a folder of files.
I can sort the folder and return all the files easily with:
return sequence.sort(files, (('bobobase_modification_time', 'cmp',
'desc'),))
How do I return just the most recent one? (I tried sorting and then using
return max(files) but that doesn't give me all the properties and I need
them for display)
Use:
return sequence.sort(files, (('bobobase_modification_time',
'cmp','desc'),))[:3]
[:3] is a slice operator which returns
item0...item2
since you sorted descenting by modification time, the
first 3 objects should be the most recent 3.
Regards
Tino
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RE: [Zope] python question
Am Dienstag, den 31.05.2005, 15:38 -0400 schrieb Jim Abramson: sort() on a sequence does not return anything. It operates on the [mutable] sequence in place. sequence is a module in Zope. So she indeed was right. ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
RE: [Zope] python question
blast! i'll keep my mouth shut til I get the library memorized. Jim -Original Message- From: Tino Wildenhain [mailto:[EMAIL PROTECTED] Sent: Tuesday, May 31, 2005 4:06 PM To: Jim Abramson Cc: Kate Legere; Zope Subject: RE: [Zope] python question Am Dienstag, den 31.05.2005, 15:38 -0400 schrieb Jim Abramson: sort() on a sequence does not return anything. It operates on the [mutable] sequence in place. sequence is a module in Zope. So she indeed was right. ___ Zope maillist - Zope@zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )
[Zope-dev] zope/python question
Hi, I saw in some products a __of__ operator and looked at the python.org for a documentation. I didn't found one. Can anybody tell me what the __of__ does ? Or tell me a URL for the documentation of the __of__ operator ? Thanks, Dirk ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] zope/python question
Dirk Datzert wrote: Hi, I saw in some products a __of__ operator and looked at the python.org for a documentation. I didn't found one. Can anybody tell me what the __of__ does ? It creates an acquisition wrapper for the object the method belongs to, in the context of the object you pass as the argument. It is part of the Extension Class package. Or tell me a URL for the documentation of the __of__ operator ? http://cvs.zope.org/~checkout~/Zope/lib/Components/ExtensionClass/doc/Acquisition.stx?rev=HEAD http://cvs.zope.org/~checkout~/Zope/lib/Components/ExtensionClass/doc/ExtensionClass.stx?rev=HEAD -- Steve Alexander ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
