Hi,
what does exactly happen when I use "python:" into a zpt?
Is it a problem if I have many "python:" in my page templates?
What are the differences in performances of these two definitions?
<metal:block tal:define="my_value my_object/getValue"></metal:block>
<metal:block tal:define="my_value
python:my_object.getValue()"></metal:block>
thank you very much
claudio :-)
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3. Juli 2006 15:05:36 +0200 Claudio Battaglino
<c.battaglino (AT) metaware (DOT) itwrote:

Hi,
what does exactly happen when I use "python:" into a zpt?
Is it a problem if I have many "python:" in my page templates?
What are the differences in performances of these two definitions?

Talking of performanceyou might write a benchmark to figure it out
no idea

<metal:block tal:define="my_value my_object/getValue"></metal:block>

<metal:block tal:define="my_value
python:my_object.getValue()"></metal:block>

The main difference between both variants is that in path expressions
getValue can be either an attribute or a methodso at least path
expressions may have some overheadyou have to measure it.
-aj

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3 Jul 2006, at 15:09, Andreas Jung wrote:

>>
><metal:block tal:define="my_value my_object/getValue"></
>metal:block>
>>
><metal:block tal:define="my_value
>python:my_object.getValue()"></metal:block>
>>
>
The main difference between both variants is that in path
expressions getValue can be either an attribute or a methodso at
least path expressions may have some overheadyou have to measure
it.

As far as I know path expressions have better performance. I don't
have the in-depth expression engine knowledge to explain why, but
that's been what everyone has said to me before.

jens

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Jens Vagelpohl ha scritto:

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3 Jul 2006, at 15:09, Andreas Jung wrote:

<metal:block tal:define="my_value my_object/getValue"></
metal:block>

<metal:block tal:define="my_value
python:my_object.getValue()"></metal:block>

>>
>The main difference between both variants is that in path expressions
>getValue can be either an attribute or a methodso at least path
>expressions may have some overheadyou have to measure it.
>
>
As far as I know path expressions have better performance. I don't
have the in-depth expression engine knowledge to explain why, but
that's been what everyone has said to me before.

jens
--
Could it be that, using a Python expression, I have an overhead because
Zope loads a Python interpreter each time it finds a "python:"?
If this is true then it is better to use path expression, if possible.

claudio :-)

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3. Juli 2006 15:38:58 +0200 Claudio Battaglino
<c.battaglino (AT) metaware (DOT) itwrote:

Jens Vagelpohl ha scritto:
>>
Could it be that, using a Python expression, I have an overhead because
Zope loads a Python interpreter each time it finds a "python:"?
If this is true then it is better to use path expression, if possible.

nahPython expression are executed in a sandbox (RestrictedPython) which
will introduce additional overheadbut let numbers speakwrite a loop in
TAL and compare the performance of path expressions vs. python
expressions don't guess, but measure
-aj

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Claudio Battaglino schrieb:
Hi,
what does exactly happen when I use "python:" into a zpt?
Is it a problem if I have many "python:" in my page templates?

Path expressions are by far better human readable IMH I try very hard
to avoid Python expressions if possible.

To give you an example:

I prefer

<option tal:attributes="selected item/selected"

over

<option tal:attributes="python: test(foo == bar, 'selected', None)"

But also because in the first example the template doesn't need to
know about implementation details and thus it is better reusable e.g. as
macro.

Tonico

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3. Juli 2006 15:50:41 +0200 Tonico Strasser <contact_tonico (AT) yahoo (DOT) de
wrote:

Claudio Battaglino schrieb:
>Hi,
>what does exactly happen when I use "python:" into a zpt?
>Is it a problem if I have many "python:" in my page templates?
>
Path expressions are by far better human readable IMH I try very hard
to avoid Python expressions if possible.

(Un)fortunately we live a in world where methods may have parameters. Path
expressions work only for parameter-less methods.
-aj

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Small correction

<option tal:attributes="python: test(foo == bar, 'selected', None)"

Should be:

<option tal:attributes="selected python: test(foo == bar, 'selected',
None)"

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Andreas Jung schrieb:

3. Juli 2006 15:50:41 +0200 Tonico Strasser
<contact_tonico (AT) yahoo (DOT) dewrote:

>Claudio Battaglino schrieb:
Hi,
what does exactly happen when I use "python:" into a zpt?
Is it a problem if I have many "python:" in my page templates?
>>
>Path expressions are by far better human readable IMH I try very hard
>to avoid Python expressions if possible.

(Un)fortunately we live a in world where methods may have parameters.
Path expressions work only for parameter-less methods.

This can be avoided if you "prepare" a namespace and pass it to the
template, this way the template doesn't need to call methods.

I've written a simple page class for doing this, but it's also possible
TTW from a Python script:

names = {'foo': 'bar'}
template = context.a_page_template
return template.pt_render(extra_context=names)

course you can still use Python expressions if needed.

Tonico

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Actually, I think python: expressions perform slightly better than
their path: counterparts because their evaluation step needs to do
less work (no guessing about getitem vs. getattr). Geoff Davis
taught me that. But in the end it's all dwarfed by the penalty
imposed by security, so it really doesn't much matter.

Jul 3, 2006, at 9:20 AM, Jens Vagelpohl wrote:

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3 Jul 2006, at 15:09, Andreas Jung wrote:

<metal:block tal:define="my_value my_object/getValue"></
metal:block>

<metal:block tal:define="my_value
python:my_object.getValue()"></metal:block>

>>
>The main difference between both variants is that in path
>expressions getValue can be either an attribute or a methodso
>at least path expressions may have some overheadyou have to
>measure it.
>
As far as I know path expressions have better performance. I don't
have the in-depth expression engine knowledge to explain why, but
that's been what everyone has said to me before.

jens
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7/3/06, Chris McDonough <chrism (AT) plope (DOT) comwrote:
Actually, I think python: expressions perform slightly better than
their path: counterparts because their evaluation step needs to do
less work (no guessing about getitem vs. getattr). Geoff Davis
taught me that. But in the end it's all dwarfed by the penalty
imposed by security, so it really doesn't much matter.

Right. So the best and quickest is to prepare all the data in pure
disk-based python.
It's easy to do if you use the view methodology you get with Five, but
there are other ways to do it if you don't want to use views.

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Andreas Jung ha scritto:

--
3. Juli 2006 15:38:58 +0200 Claudio Battaglino
<c.battaglino (AT) metaware (DOT) itwrote:
>
>Jens Vagelpohl ha scritto:
>>

>Could it be that, using a Python expression, I have an overhead because
>Zope loads a Python interpreter each time it finds a "python:"?
>If this is true then it is better to use path expression, if possible.
>>
>
nahPython expression are executed in a sandbox (RestrictedPython)
which will introduce additional overheadbut let numbers
speakwrite a loop in TAL and compare the performance of path
expressions vs. python expressions don't guess, but measure

-aj

It seems that the Python Expression works a bit better:

To the test this, I used these two Page Templates and PTProfiler:

PATH EXPRESSIN
<div tal:define="test_user " tal:repeat="counter python:range(5000)">
<span tal:content="test_user/getId" />
</div>

PYTHN EXPRESSIN
<div tal:define="test_user " tal:repeat="counter python:range(5000)">
<span tal:content="python: test_user.getId()" />
</div>

PATH EXPRESSIN
Expression - Total time - Number of calls - Time per call
path: test_user/getId 0.72 5000 0.00014
path: test_user/getId 0.63 5000 0.00013
path: test_user/getId 0.72 5000 0.00014

path: test_user/getId 4.0 50000 8e-05
path: test_user/getId4.09500008e-05
path: test_user/getId 4.12 50000 8e-05

PYTHN EXPRESSIN
Expression - Total time - Number of calls - Time per call
python: test_user.getId() 0.6 5000 0.00012
python: test_user.getId() 0.51 5000 0.0001
python: test_user.getId() 0.48 5000 0.0001
python: test_user.getId() 3.19 50000 6e-05
python: test_user.getId() 3.42 50000 7e-05
python: test_user.getId() 2.96 50000 6e-05

Is it a significant test?

claudio :-)

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Lennart Regebro wrote:
7/3/06, Chris McDonough
<chrism (AT) plope (DOT) comwrote:
>Actually, I think python: expressions perform slightly better than
>their path: counterparts because their evaluation step needs to do
>less work (no guessing about getitem vs. getattr). Geoff Davis
>taught me that. But in the end it's all dwarfed by the penalty
>imposed by security, so it really doesn't much matter.

Right. So the best and quickest is to prepare all the data in pure
disk-based python.
It's easy to do if you use the view methodology you get with Five, but
there are other ways to do it if you don't want to use views.

My 'pushpage' package is an attempt to make this the "standard" pattern
(pushpage templates don't have *any* top-level names available to them
(i.e., 'context', 'container', 'request', etc.) except those passed to
their '__call__' as keyword arguments (which traditional ZPT exposes
under 'options'):

The templates can be used from within methods of view classes, and can
also be published as "pages" via ZCML with the help of a user-defined
callable which computes the keyword arguments. E.g.:

<pushpage:view
for=""
name="somepage.html"
permission="zope.Public"
template="templates/sometemplate.pt"
mapping=".somemodule,somefunction"
layer="mylayer"
/>

In this example, 'somemodule.somefunction' returns the mapping which
'sometemplate' will use as its top-level namespace. The callable is
passed 'context' and 'request' as arguments.

Tres.
- --
Tres Seaver +1 202-558-7113 tseaver (AT) palladion (DOT) com
Palladion Software "Excellence by Design" http://palladion.com
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