## From Django 1.7 onwards

Django has built in support for migrations - take a look at [the documentation](https://docs.djangoproject.com/en/dev/topics/migrations/).

## For Django 1.6 and earlier

Django doesn&#39;t support migrations out of the box. There is a pluggable app for Django that does exactly that though, and it works great. It&#39;s called [South](http://south.aeracode.org).


Django currently does not do this automatically. Your options are:

1. Drop the table from the database, then recreate it in new form using syncdb.
2. Print out SQL for the database using &lt;code&gt;python manage.py sql (appname)&lt;/code&gt;, find the added line for the field and add it manually using &lt;code&gt;alter table&lt;/code&gt; SQL command. (This will also allow you to choose values of the field for your current records.)
3. Use &lt;a href=&quot;http://south.aeracode.org/&quot;&gt;South&lt;/a&gt; (per &lt;a href=&quot;https://stackoverflow.com/questions/1605662/django-syncdb-and-an-updated-model/1605673#1605673&quot;&gt;Dominic&#39;s answer&lt;/a&gt;).

Follow these steps:

 1. Export your data to a fixture using the [dumpdata][1] management command
 2. Drop the table
 3. Run syncdb
 4. Reload your data from the fixture using the [loaddata][2] management command


  [1]: http://docs.djangoproject.com/en/dev/ref/django-admin/?from=olddocs#dumpdata
  [2]: http://docs.djangoproject.com/en/dev/ref/django-admin/?from=olddocs#loaddata-fixture-fixture

As suggested in top answer, I tried using [South][1], and after an hour of frustration with [obscure migration errors][2] decided to go with [Django Evolution][3] instead.

I think it&#39;s easier to get started with than South, and it worked perfectly the first time I typed `./manage.py evolve --hint --execute`, so I&#39;m happy with it.


  [1]: http://south.aeracode.org/
  [2]: https://stackoverflow.com/questions/4840102/how-come-my-south-migrations-doesnt-work-for-django
  [3]: http://code.google.com/p/django-evolution/

Havent used django in a while, but i seem to remember that syncdb does perform alter commands on db tables. you have to drop the table then run again and it will create again.

edit: sorry does NOT perform alter.

In django **1.6**
 
 - At first we have run - `python manage.py sql &lt;app name&gt;`
 
 - Then we have to run - `python manage.py syncdb`

If you run Django with Apache and MySQL, restart apache after making migration with *makemigrations*.

What is the difference between **`include`** and **`extend`** in a [use case diagram][1]?

  [1]: http://en.wikipedia.org/wiki/Use_case_diagram


What&#39;s is the difference between include and extend in use case diagram?

When I do `(/ 411 125)` , I don&#39;t get it in terms of decimal. How do I do that?

When I divide numbers in clojure I get a fraction , how do I get the decimal?

I have recently updated my model, added a BooleanField to it however when I do `python manage.py syncdb`, it doesn&#39;t add the new field to the database for the model. How can I fix this ?

django syncdb and an updated model

<p>I have recently updated my model, added a BooleanField to it however when I do <code>python manage.py syncdb</code>, it doesn't add the new field to the database for the model. How can I fix this ?</p>


Is it possible to add a documentation string to a namedtuple in an easy manner?

I tried

    from collections import namedtuple

    Point = namedtuple(&quot;Point&quot;, [&quot;x&quot;, &quot;y&quot;])
    &quot;&quot;&quot;
    A point in 2D space
    &quot;&quot;&quot;

    # Yet another test

    &quot;&quot;&quot;
    A(nother) point in 2D space
    &quot;&quot;&quot;
    Point2 = namedtuple(&quot;Point2&quot;, [&quot;x&quot;, &quot;y&quot;])

    print Point.__doc__ # -&gt; &quot;Point(x, y)&quot;
    print Point2.__doc__ # -&gt; &quot;Point2(x, y)&quot;

but that doesn&#39;t cut it. Is it possible to do in some other way?

Adding docstrings to namedtuples?

I want to `subprocess.Popen()` rsync.exe in Windows, and print the stdout in Python.

My code works, but it doesn&#39;t catch the progress until a file transfer is done! I want to print the progress for each file in real time.

Using Python 3.1 now since I heard it should be better at handling IO.


    import subprocess, time, os, sys
     
    cmd = &quot;rsync.exe -vaz -P source/ dest/&quot;
    p, line = True, &#39;start&#39;
     
     
    p = subprocess.Popen(cmd,
                         shell=True,
                         bufsize=64,
                         stdin=subprocess.PIPE,
                         stderr=subprocess.PIPE,
                         stdout=subprocess.PIPE)
     
    for line in p.stdout:
        print(&quot;&gt;&gt;&gt; &quot; + str(line.rstrip()))
        p.stdout.flush()



catching stdout in realtime from subprocess

In Python, how do you make a subclass from a superclass?

Python: How do I make a subclass from a superclass?

I had a strange bug when porting a feature to the Python 3.1 fork of my program. I narrowed it down to the following hypothesis:

In contrast to Python 2.x, in Python 3.x if an object has an `__eq__` method it is automatically unhashable.

Is this true?

Here&#39;s what happens in Python 3.1:

    &gt;&gt;&gt; class O(object):
    ...     def __eq__(self, other):
    ...         return &#39;whatever&#39;
    ...
    &gt;&gt;&gt; o = O()
    &gt;&gt;&gt; d = {o: 0}
    Traceback (most recent call last):
      File &quot;&lt;pyshell#16&gt;&quot;, line 1, in &lt;module&gt;
        d = {o: 0}
    TypeError: unhashable type: &#39;O&#39;

The follow-up question is, how do I solve my personal problem? I have an object `ChangeTracker` which stores a `WeakKeyDictionary` that points to several objects, giving for each the value of their pickle dump at a certain time point in the past. Whenever an existing object is checked in, the change tracker says whether its new pickle is identical to its old one, therefore saying whether the object has changed in the meantime. Problem is, now I can&#39;t even check if the given object is in the library, because it makes it raise an exception about the object being unhashable. (Cause it has a `__eq__` method.) How can I work around this?


Types that define `__eq__` are unhashable?

I have tried to use Python&#39;s [ConfigParser][1] module to save settings. For my app it&#39;s important that I preserve the case of each name in my sections. The docs mention that passing str() to [ConfigParser.optionxform()][2] would accomplish this, but it doesn&#39;t work for me. The names are all lowercase. Am I missing something?

    &lt;~/.myrc contents&gt;
    [rules]
    Monkey = foo
    Ferret = baz

Python pseudocode of what I get:

    import ConfigParser,os

    def get_config():
       config = ConfigParser.ConfigParser()
       config.optionxform(str())
        try:
            config.read(os.path.expanduser(&#39;~/.myrc&#39;))
            return config
        except Exception, e:
            log.error(e)

    c = get_config()  
    print c.options(&#39;rules&#39;)
    [(&#39;monkey&#39;, &#39;foo&#39;), (&#39;ferret&#39;, &#39;baz&#39;)]
    


  [1]: http://docs.python.org/library/configparser.html
  [2]: http://docs.python.org/library/configparser.html#ConfigParser.RawConfigParser.optionxform

Preserve case in ConfigParser?

In Django&#39;s admin, I want _disable_ the links provided on the &quot;select item to change&quot; page so that users cannot go anywhere to edit the item.  (I am going to limit what the users can do with this list to a set of drop down actions - no actual editing of fields).

I see that Django has the ability to [choose which fields display the link][1], however, I can&#39;t see how I can have **none** of them.  

    class HitAdmin(admin.ModelAdmin):
        list_display = (&#39;user&#39;,&#39;ip&#39;,&#39;user_agent&#39;,&#39;hitcount&#39;)
        search_fields = (&#39;ip&#39;,&#39;user_agent&#39;)
        date_hierarchy = &#39;created&#39;
        list_display_links = [] # doesn&#39;t work, goes to default

Any ideas how to get my object list without any links to edit?

  [1]: http://docs.djangoproject.com/en/dev/ref/contrib/admin/#django.contrib.admin.ModelAdmin.list_display_links

Disable link to edit object in django&#39;s admin (display list only)?

We&#39;ve got a server over which we&#39;re running a Django powered site. Since we want to test the site, we&#39;re using Django&#39;s build-in development server (i.e `runserver`).  But I&#39;m curious about the ip of the following command:

    python manage.py runserver 0.0.0.0:80

It results in a running site we can visit using server&#39;s ip remotely.  
But when using `127.0.0.1` instead:

    python manage.py runserver 127.0.0.1:80

No one can visit the site with the sever&#39;s ip from another pc.

So why? What does `0.0.0.0` exactly means (Google says it&#39;s the default route) ?  Why can&#39;t `127.0.0.1:80` be accessed remotely?

About IP 0.0.0.0 in Django

How do I find the previous Monday&#39;s date, based off of the current date using Python? I thought maybe I could use: `datetime.weekday()` to do it, but I am getting stuck.

I basically want to find today&#39;s date and Mondays date to construct a date range query in django using: `created__range=(start_date, end_date)`.  

Find Monday&#39;s date with Python

I have a web site which shows different content based on a location
the visitor chooses. e.g: User enters in 55812 as the zip. I know what
city and area lat/long. that is and give them their content pertinent
to that area. My question is how can I store this in a cookie so that
when they return they are not required to always enter their zip code?

I see it as follows:

1. Set persistent cookie based on their area.
2. When they return read cookie, grab zipcode.
3. Return content based on the zip code in their cookie.

I can&#39;t seem to find any solid information on setting a cookie. Any
help is greatly appreciated. 

Django Cookies, how can I set them?

Where should the validation of _model fields_ go in django?

I could name at least two possible choices: in the overloaded .save() method of the model or in the .to_python() method of the models.Field subclass (obviously for that to work you must write custom fields).

Possible use cases:

 - when it is absolutely neccessary to ensure, that an empty string doesn&#39;t get written into the database (blank=False keyword argument doesn&#39;t work here, it is for form validation only)
 - when it is neccessary to ensure, that &quot;choices&quot; keyword argument gets respected on a db-level and not only in admin interface (kind of emulating a enum datatype)

There is also a class-level attribute `empty_strings_allowed` in the models.Field base class definition and derived classes happily override it, however it doesn&#39;t seem to produce any effect on the database level, meaning I can still construct a model with empty-string fields and save it to the database. Which I want to avoid (yes, it is neccessary).

Possible implementations are

on the field level:

    class CustomField(models.CharField):
        __metaclass__ = models.SubfieldBase
        def to_python(self, value):
            if not value:
                raise IntegrityError(_(&#39;Empty string not allowed&#39;))
            return models.CharField.to_python(self, value)

on the model level:

    class MyModel(models.Model)
        FIELD1_CHOICES = [&#39;foo&#39;, &#39;bar&#39;, &#39;baz&#39;]
        field1 = models.CharField(max_length=255, 
                   choices=[(item,item) for item in FIELD1_CHOICES])
        
        def save(self, force_insert=False, force_update=False):
            if self.field1 not in MyModel.FIELD1_CHOICES:
                raise IntegrityError(_(&#39;Invalid value of field1&#39;))
            # this can, of course, be made more generic
            models.Model.save(self, force_insert, force_update)

Perhaps, I am missing something and this can be done easier (and cleaner)?


Django model fields validation

I have two models in different apps: `ModelA` and `ModelB`.  They have a one-to-one relationship.  Is there a way django can automatically create and save `ModelB` when `ModelA` is saved?

    class ModelA(models.Model):
        name = models.CharField(max_length=30)

    class ModelB(models.Model):
        thing = models.OneToOneField(ModelA, primary_key=True)
        num_widgets = IntegerField(default=0)

When I save a new `ModelA` I want a entry for it to be saved automatically in `ModelB`.  How can I do this?  Is there a way to specify that in `ModelA`?  Or is this not possible, and I would just need to create and save `ModelB` in the view?

Edited to say the models are in different apps.


Can Django automatically create a related one-to-one model?

For Django 1.1.

I have this in my models.py:

    class User(models.Model):
        created = models.DateTimeField(auto_now_add=True)
        modified = models.DateTimeField(auto_now=True)

When updating a row I get:

    [Sun Nov 15 02:18:12 2009] [error] /home/ptarjan/projects/twitter-meme/django/db/backends/mysql/base.py:84: Warning: Column &#39;created&#39; cannot be null
    [Sun Nov 15 02:18:12 2009] [error]   return self.cursor.execute(query, args)

The relevant part of my database is:

      `created` datetime NOT NULL,
      `modified` datetime NOT NULL,

Is this cause for concern?

Side question: in my admin tool, those two fields aren&#39;t showing up. Is that expected?


Django auto_now and auto_now_add

Say I have a Django class something like this:

    class Person(models.Model):
        name = models.CharField(max_length=50)
        # ...

How can I programatically obtain the `max_length` value for the `name` field?


How can I programmatically obtain the max_length of a Django model field?

I&#39;m trying to filter a table in Django based on the value of a particular field of a `ForeignKey`.

For example, I have two models:

    class Asset(models.Model):
        name = models.TextField(max_length=150)
        project = models.ForeignKey(&#39;Project&#39;)

    class Project(models.Model):
        name = models.TextField(max_length=150)

I&#39;d like to filter my asset list based on the name of the associated project.

Currently, I am performing **two** queries:


    project_list = Project.objects.filter(name__contains=&quot;Foo&quot;)
    asset_list = Asset.objects.filter(desc__contains=filter,
                                      project__in=project_list).order_by(&#39;desc&#39;)

I&#39;m wondering if there is a way to specify this kind of filtering in the main query?


Content Type	Original Author	Original Content on Stackoverflow
Question	Hellnar	View Question on Stackoverflow
Solution 1 - Python	Dominic Rodger	View Answer on Stackoverflow
Solution 2 - Python	che	View Answer on Stackoverflow
Solution 3 - Python	Soviut	View Answer on Stackoverflow
Solution 4 - Python	Dan Abramov	View Answer on Stackoverflow
Solution 5 - Python	Alex H	View Answer on Stackoverflow
Solution 6 - Python	Monwara Hossain Munni	View Answer on Stackoverflow
Solution 7 - Python	Felipe Perry	View Answer on Stackoverflow

django syncdb and an updated model

Python Problem Overview

Python Solutions

Solution 1 - Python

From Django 1.7 onwards

For Django 1.6 and earlier

Solution 2 - Python

Solution 3 - Python

Solution 4 - Python

Solution 5 - Python

Solution 6 - Python

Solution 7 - Python

When I divide numbers in clojure I get a fraction , how do I get the decimal?

What's is the difference between include and extend in use case diagram?

Attributions