You want the `default_if_none` template filter, ([doc][default-filter]).

`default_if_none` will display the given string if the variable is &#39;None&#39;.

`default` will display the string if the variable evaluates to False, ie empty strings, empty lists etc

    {{ item.somefield|default_if_none:&quot;&quot; }}
    {{ item.somefield|default:&quot;&quot; }}

  [default-filter]: https://docs.djangoproject.com/en/dev/ref/templates/builtins/#default-if-none

[This earlier question][1] addresses some of the factors that might cause an algorithm to have O(log n) complexity.

What would cause an algorithm to have time complexity O(log log n)?


  [1]: https://stackoverflow.com/questions/9152890/what-would-cause-an-algorithm-to-have-olog-n-complexity

What would cause an algorithm to have O(log log n) complexity?

We&#39;re ending up with a lot of commits like this in our repo:

    Merge branch &#39;master&#39; of bitbucket.org:user/repo

This happens every time a developer syncs his/hers local fork to the top-level repo.

Is there anyway to avoid this merge-commit hell from cluttering all the repo log? Can one avoid them when initiating the pull-requests in some way?

I know I can do git rebase if this is done in my local VM only, is there any equivalence in the GitHub/BitBucket UI?

How do you guys do it?

How to avoid merge-commit hell on GitHub/BitBucket

My code in template is like this:

    {% for item in items %}
        {{ item.somefield }}
    {% endfor %}

I want to display the item value if the item.somefield is not None, or display an empty string. I don&#39;t want to use the {% if item.somefield %} statement, I want something like {{ item.somefield or &#39;&#39; }}(I tried this but it doesn&#39;t work)


django template display item value or empty string

My code in template is like this:
<pre><code class="hljs language-markdown">{% for item in items %}
 {{ item.somefield }}
{% endfor %}
</code></pre>
I want to display the item value if the item.somefield is not None, or display an empty string. I don't want to use the {% if item.somefield %} statement, I want something like {{ item.somefield or '' }}(I tried this but it doesn't work)

I am trying to instal virtualenv and/or virtualenvwrapper on a mac osx 10.8.3

I have been fighting with python for the last two days. Finally I was able to install python 2.7.4 using brew.  Before I had virtualenv installed using easy_install. Then I tried to uninstall it, trying to get my computer in the same situation as the one of my colleagues. Maybe I uninstalled it with success, maybe not. I don&#39;t know how to test it. Now I am supposed to install virtualenv using -

    pip install virtualenv

But it gives me -

    Could not find an activated virtualenv (required).

`pip install virtualenvwrapper` gives exactly the same output.

Also the variable: `PIP_RESPECT_VIRTUALENV` is null:

    echo $PIP_RESPECT_VIRTUALENV

How can I solve this issue?

Thanks

pip: Could not find an activated virtualenv (required)

Is there a way to memoize the output of a function to disk?

I have a function

    def getHtmlOfUrl(url):
        ... # expensive computation


and would like to do something like:

    def getHtmlMemoized(url) = memoizeToFile(getHtmlOfUrl, &quot;file.dat&quot;)

and then call getHtmlMemoized(url), so as to do the expensive computation only once for each url.


memoize to disk - python - persistent memoization

Is there a standard way, in Python, to normalize a unicode string, so that it only comprehends the simplest unicode entities that can be used to represent it ?

I mean, something which would translate a sequence like `[&#39;LATIN SMALL LETTER A&#39;, &#39;COMBINING ACUTE ACCENT&#39;]` to `[&#39;LATIN SMALL LETTER A WITH ACUTE&#39;]` ?

See where is the problem:

    &gt;&gt;&gt; import unicodedata
    &gt;&gt;&gt; char = &quot;&#225;&quot;
    &gt;&gt;&gt; len(char)
    1
    &gt;&gt;&gt; [ unicodedata.name(c) for c in char ]
    [&#39;LATIN SMALL LETTER A WITH ACUTE&#39;]

But now:

    &gt;&gt;&gt; char = &quot;á&quot;
    &gt;&gt;&gt; len(char)
    2
    &gt;&gt;&gt; [ unicodedata.name(c) for c in char ]
    [&#39;LATIN SMALL LETTER A&#39;, &#39;COMBINING ACUTE ACCENT&#39;]

I could, of course, iterate over all the chars and do manual replacements, etc., but it is not efficient, and I&#39;m pretty sure I would miss half of the special cases, and do mistakes.

Normalizing Unicode

I want to be able to iterate over the matrix to apply a function to each row. How can I do it for a Numpy matrix ? 

Iterating over Numpy matrix rows to apply a function each?

What exactly is the difference between numpy `vstack` and `column_stack`. Reading through the documentation, it looks as if `column_stack` is an implementation of `vstack` for 1D arrays. Is it a more efficient implementation? Otherwise, I cannot find a reason for just having `vstack`.

numpy vstack vs. column_stack

Besides the syntax, what&#39;s the difference between using a django abstract model and using plain Python inheritance with django models?  Pros and cons?

UPDATE: I think my question was misunderstood and I received responses for the difference between an abstract model and a class that inherits from django.db.models.Model.   **I actually want to know the difference between a model class that inherits from a django abstract class (Meta: abstract = True) and a plain Python class that inherits from say, &#39;object&#39; (and not models.Model).**


Here is an example:

    class User(object):
       first_name = models.CharField(..

       def get_username(self):
           return self.username

    class User(models.Model):
       first_name = models.CharField(...

       def get_username(self):
           return self.username

       class Meta:
           abstract = True
  
    class Employee(User):
       title = models.CharField(...

django abstract models versus regular inheritance

I&#39;m currently migrating all the static files references in my project to the new {% static %} tag that django 1.5 introduced, but I&#39;m having a problem, in some places I use variables to get the content. With the new tag I can&#39;t, is there any way to solve this?

Current code:

    &lt;img src=&quot;{{ STATIC_URL }}/assets/flags/{{ request.LANGUAGE_CODE }}.gif&quot; alt=&quot;{% trans &#39;Language&#39; %}&quot; title=&quot;{% trans &#39;Language&#39; %}&quot; /&gt;

What it should be (this doesn&#39;t work):

    &lt;img src=&quot;{% static &#39;assets/flags/{{ request.LANGUAGE_CODE }}.gif&#39; %}&quot; alt=&quot;{% trans &#39;Language&#39; %}&quot; title=&quot;{% trans &#39;Language&#39; %}&quot; /&gt;



django 1.5 - How to use variables inside static tag

I have quite a simple problem to solve. I have Partner model which has &gt;= 0 Users associated with it:

    class Partner(models.Model):
        name = models.CharField(db_index=True, max_length=255)
        slug = models.SlugField(db_index=True)
        user = models.ManyToManyField(User)


Now, if I have a User object and I have a Partner object, what is the most Pythonic way of checking if the User is associated with a Partner? I basically want a statement which returns True if the `User` is associated to the `Partner`. 

I have tried:

    users = Partner.objects.values_list(&#39;user&#39;, flat=True).filter(slug=requested_slug)
    if request.user.pk in users:
        # do some private stuff

This works but I have a feeling there is a better way. Additionally, would this be easy to roll into a decorator, baring in mind I need both a named parameter (`slug`) and a request object (`user`).


Django check if object in ManyToMany field

I have the following code for serializing the queryset;

    def render_to_response(self, context, **response_kwargs):

        return HttpResponse(json.simplejson.dumps(list(self.get_queryset())),
                            mimetype=&quot;application/json&quot;)

And following is my `get_querset()`

    [{&#39;product&#39;: &lt;Product: hederello ()&gt;, u&#39;_id&#39;: u&#39;9802&#39;, u&#39;_source&#39;: {u&#39;code&#39;: u&#39;23981&#39;, u&#39;facilities&#39;: [{u&#39;facility&#39;: {u&#39;name&#39;: {u&#39;fr&#39;: u&#39;G\xe9n\xe9ral&#39;, u&#39;en&#39;: u&#39;General&#39;}, u&#39;value&#39;: {u&#39;fr&#39;: [u&#39;bar&#39;, u&#39;r\xe9ception ouverte 24h/24&#39;, u&#39;chambres non-fumeurs&#39;, u&#39;chambres familiales&#39;,.........]}]


Which I need to serialize. But it says not able to serialize the `&lt;Product: hederello ()&gt;`. Because list composed of both django objects and dicts. Any ideas ? 

&lt;Django object &gt; is not JSON serializable

I have a model like this:

    class Hop(models.Model):
        migration = models.ForeignKey(&#39;Migration&#39;)
        host = models.ForeignKey(User, related_name=&#39;host_set&#39;)

How can I have the primary key be the combination of `migration` and `host`?







How can I set two primary key fields for my models in Django?

I&#39;m writing a ToDo list app to help myself get started with Python. The app is running on GAE and I&#39;m storing todo items in the Data Store. I want to display everyone&#39;s items to them, and them alone. The problem is that the app currently displays all items to all users, so I can see what you write, and you see what I write. I thought casting my todo.author object to a string and seeing if it matches the user&#39;s name would be a good start, but I can&#39;t figure out how to do that. 

This is what I have in my main.py

    ...	
    user = users.get_current_user()

	if user:
	    nickname = user.nickname()
	    todos = Todo.all()
	    template_values = {&#39;nickname&#39;:nickname, &#39;todos&#39;:todos}
    ...

    def post(self):

	    todo = Todo()
	    todo.author = users.get_current_user()
	    todo.item = self.request.get(&quot;item&quot;)
	    todo.completed = False

	    todo.put()		
	    self.redirect(&#39;/&#39;)

In my index.html I had this originally: 

    &lt;input type=&quot;text&quot; name=&quot;item&quot; class=&quot;form-prop&quot; placeholder=&quot;What needs to be done?&quot; required/&gt;
    ...
     &lt;ul&gt;
	{% for todo in todos %}
      &lt;input type=&quot;checkbox&quot;&gt; {{todo.item}} &lt;hr /&gt;
    {% endfor %}
	&lt;/ul&gt;

but I&#39;d like to display items only to the user who created them. I thought of trying 

    {% for todo in todos %}
		{% ifequal todo.author nickname %}
      &lt;input type=&quot;checkbox&quot;&gt; {{todo.item}} &lt;hr /&gt;
		{% endifequal %}
    {% endfor %}

to no avail. The list turns up blank. I assumed it is because todo.author is not a string. Can I read the value out as a string, or can I cast the object to String?

Thanks!

Edit: Here is my Todo class

    class Todo(db.Model):
        author = db.UserProperty()
        item = db.StringProperty()
        completed = db.BooleanProperty()
        date = db.DateTimeProperty(auto_now_add=True)

Will changing my author to a StringProperty effect anything negatively? Maybe I can forgo casting altogether.

Does Python have a toString() equivalent, and can I convert a class to String?

How can I get information about the logged-in user in a Django application?

For example: 

I need to know the username of the logged-in user to say who posted a Review:

    &lt;form id=&#39;formulario&#39; method=&#39;POST&#39; action=&#39;&#39;&gt;
    	&lt;h2&gt;Publica tu tuit, {{ usuario.username.title }} &lt;/h2&gt;
    	{% csrf_token %}
    	{{formulario.as_p}}
    	&lt;p&gt;&lt;input type=&#39;submit&#39; value=&#39;Confirmar&#39; /&gt;&lt;/p&gt;
    &lt;/form&gt;

In `usuario.username.title` I get the username, but in the template, I need to get that information from the view. 

How can I get the username of the logged-in user in Django?

Following the tutorial found &lt;a href=&quot;https://docs.djangoproject.com/en/dev/intro/tutorial03/&quot;&gt;here&lt;/a&gt; exactly, I cannot create a custom 500 or 404 error page. If I do type in a bad url, the page gives me the default error page. Is there anything I should be checking for that would prevent a custom page from showing up?


File directories:

    mysite/
        mysite/
            __init__.py
            __init__.pyc
            settings.py
            settings.pyc
            urls.py
            urls.pyc
            wsgi.py
            wsgi.pyc
        polls/
            templates/
                admin/
                    base_site.html
                404.html
                500.html
                polls/
                    detail.html
                    index.html
            __init__.py
            __init__.pyc
            admin.py
            admin.pyc
            models.py
            models.pyc
            tests.py
            urls.py
            urls.pyc
            view.py
            views.pyc
        templates/
        manage.py
        

within mysite/settings.py I have these enabled:
    

    DEBUG = False
    TEMPLATE_DEBUG = DEBUG

    #....

    TEMPLATE_DIRS = (
        &#39;C:/Users/Me/Django/mysite/templates&#39;, 
    )

within mysite/polls/urls.py:

    from django.conf.urls import patterns, url

    from polls import views

    urlpatterns = patterns(&#39;&#39;,
        url(r&#39;^$&#39;, views.index, name=&#39;index&#39;),
        url(r&#39;^(?P&lt;poll_id&gt;\d+)/$&#39;, views.detail, name=&#39;detail&#39;),
        url(r&#39;^(?P&lt;poll_id&gt;\d+)/results/$&#39;, views.results, name=&#39;results&#39;),
        url(r&#39;^(?P&lt;poll_id&gt;\d+)/vote/$&#39;, views.vote, name=&#39;vote&#39;),
    )


I can post any other code necessary, but what should I be changing to get a custom 500 error page if I use a bad url?


**Edit**

**SOLUTION:**
I had an additional

    TEMPLATE_DIRS

within my settings.py and that was causing the problem

Django, creating a custom 500/404 error page

I&#39;m a django beginner so I&#39;m trying to understand the concept of context and context processor.

- What is a context and why do you use it? 
- Is a context a value you need to have available in order to use in a template?
- Is a context and a context processor the same?

I&#39;ll apreciate a lot your response. Thanks in advance!

Content Type	Original Author	Original Content on Stackoverflow
Question	Roger Liu	View Question on Stackoverflow
Solution 1 - Python	rockingskier	View Answer on Stackoverflow
Solution 2 - Python	matino	View Answer on Stackoverflow

django template display item value or empty string

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

How to avoid merge-commit hell on GitHub/BitBucket

What would cause an algorithm to have O(log log n) complexity?

Attributions