It is not possible: &quot;the render() method is the only traversable in grok.codeView classes&quot;

as stated in: https://developer.plone.org/templates_css_and_javascripts/javascript.html

I&#39;m building a system where multiple slave processes are communicating via unix domain sockets, and they are writing to the **same file** at the same time.  I have never studied filesystems or this specific filesystem (ext4), but it feels like there might be some danger here.

Each process writes to a disjoint subset of the output file (ie, there is no overlap in the blocks being written).   For example, `P1` writes to only the first 50% of the file and `P2` writes only to the second 50%.  Or perhaps `P1` writes only the odd-numbered blocks while `P2` writes the even-numbered blocks.

Is it safe to have `P1` and `P2` (running simultaneously on separate threads) writing to the same file without using any locking?  In other words, does the filesystem impose some kind of locking implicitly?

**Note:** I&#39;m unfortunately not at liberty to output multiple files and join them later.

**Note:** My reading since posting this question does not agree with the only posted answer below.  Everything I&#39;ve read suggests that what I want to do is fine, whereas the respondent below insists what I am doing is unsafe, but I am unable to discern the described danger.

Safe to have multiple processes writing to the same file at the same time? [CentOs 6, ext4]

I have basically a username is unique (case insensitive), but the case matters when displaying as provided by the user. 

I have the following requirements:

+ field is CharField compatible
+ field is unique, but case insensitive
+ field needs to be searchable ignoring case (avoid using iexact, easily forgotten)
+ field is stored with case intact 
+ preferably enforced on database level
+ preferably avoid storing an extra field

Is this possible in Django? 

The only solution I came up with is &quot;somehow&quot; override the Model manager, use an extra field, or always use &#39;iexact&#39; in searches.

I&#39;m on Django 1.3 and PostgreSQL 8.4.2.

Case insensitive unique model fields in Django?

Is there a way to mark methods traversable in `grok.CodeView` classes, like you can do with Zope 3 BrowserView and `allowed_attributes` ZCML configuration directive? 

I found docs about `grok.traversable()` but it looks like such method does not exist in five grok package.

ZCML allowed_attributes corresponding method in five.grok

<p>Is there a way to mark methods traversable in <code>grok.CodeView</code> classes, like you can do with Zope 3 BrowserView and <code>allowed_attributes</code> ZCML configuration directive?</p>
<p>I found docs about <code>grok.traversable()</code> but it looks like such method does not exist in five grok package.</p>


I have a base class `Person` and derived classes `Manager` and `Employee`. Now, what I would like to know is the object created is `Manager` or the `Employee`.

The person is given as belows:

    from Project.CMFCore.utils import getToolByName
    schema = getattr(Person, &#39;schema&#39;, Schema(())).copy() + Schema((TextField(&#39;FirstName&#39;, required = True, widget = StringWidget(label=&#39;First Name&#39;, i18n_domain=&#39;project&#39;)), TextField(&#39;Last Name&#39;, required = True, widget = StringWidget(label=&#39;Last Name&#39;, i18n_domain=&#39;i5&#39;, label_msgid=&#39;label_pub_city&#39;))
    class Manager(BaseContent):
      def get_name(self):
        catalog = getToolByName(self, &quot;portal_catalog&quot;)
          people = catalog(portal_type=&#39;Person&#39;)
          person={}
          for object in people:
            fname = object.firstName
            lname = object.lastName
            person[&#39;name&#39;] = fname+&#39; &#39;+ lname
            # if the derived class is Employee then i would like go to the method title of employee and if its a Manager then go to the title method of Manager
            person[&#39;post&#39;] = Employee/Manager.title()
          return person

For Manager and employees they are like (employee is also similar but some different methods)

    from Project.Person import Person
    class Manager(Person):
        def title(self):
          return &quot;Manager&quot;

For Employee the title is &#39;Employee&#39;. When I create a `Person` it is either `Manager` or the `Employee`. When I get the person object the class is Person but I would like to know whether it is from the derived class &#39;Manager&#39; or &#39;Employee&#39;.


how to get derived class name from base class

I think this problem is not Zope-related. Nonetheless I&#39;ll explain what I&#39;m trying to do:

I&#39;m using a PUT_factory in Zope to upload images to the ZODB per FTP. The uploaded image is saved as a Zope Image inside a newly created container object. This works fine, but I want to resize the image if it exceeds a certain size (width and height). So I&#39;m using the thumbnail function of PIL to resize them i.e. to 200x200. This works fine as long as the uploaded images are relatively small. I didn&#39;t check out the exact limit, but 976x1296px is still ok.

With bigger pictures I get: 

    Module PIL.Image, line 1559, in thumbnail
    Module PIL.ImageFile, line 201, in load
    IOError: image file is truncated (nn bytes not processed).

I tested a lot of jpegs from my camera. I don&#39;t think they are all truncated.

Here is my code:

    if img and img.meta_type == &#39;Image&#39;:
      pilImg = PIL.Image.open( StringIO(str(img.data)) )
    elif imgData:
      pilImg = PIL.Image.open( StringIO(imgData) )

    pilImg.thumbnail((width, height), PIL.Image.ANTIALIAS)

As I&#39;m using a PUT_factory, I don&#39;t have a file object, I&#39;m using either the raw data from the factory or a previously created (Zope) Image object.

I&#39;ve heard that PIL handles image data differently when a certain size is exceeded, but I don&#39;t know how to adjust my code. Or is it related to PIL&#39;s lazy loading?

PIL &quot;IOError: image file truncated&quot; with big images

How can I use Chameleon or Zope Page Templates to easily create CSS zebra striping? I want to add `odd` and `even` classes to each row in a table, but using a condition with `repeat/name/odd` or `repeat/name/even` looks rather verbose even with a conditional expression:

&lt;!-- language: lang-html --&gt;

    &lt;table&gt;
       &lt;tr tal:repeat=&quot;row rows&quot; 
           tal:attributes=&quot;class python:repeat[&#39;row&#39;].odd and &#39;odd&#39; or &#39;even&#39;&quot;&gt;
           &lt;td tal:repeat=&quot;col row&quot; tal:content=&quot;col&quot;&gt;column text text&lt;/td&gt;
       &lt;/tr&gt;
    &lt;/table&gt;

This gets especially tedious if you have multiple classes to calculate.



Content Type	Original Author	Original Content on Stackoverflow
Question	Mikko Ohtamaa	View Question on Stackoverflow
Solution 1 - Plone	Max Langerak	View Answer on Stackoverflow

ZCML allowed_attributes corresponding method in five.grok

Plone Problem Overview

Plone Solutions

Solution 1 - Plone

Case insensitive unique model fields in Django?

Safe to have multiple processes writing to the same file at the same time? [CentOs 6, ext4]

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