If you have something like:

    mytable = Table(&#39;mytable&#39;, db.metadata,
        Column(&#39;id&#39;, db.Integer, primary_key=True),
        Column(&#39;counter&#39;, db.Integer)
    )

You can increment fields like this:

    m = mytable.query.first()
    m.counter = mytable.c.counter + 1

Or, if you have some mapped Models, you can write alternatively:

    m = Model.query.first()
    m.counter = Model.counter + 1

Both versions will return the sql statement you have asked for. But if you don&#39;t include the column and just write `m.counter += 1`, then the new value would be calculated in Python (and race conditions are likely to happen). So always include a column as shown in the two examples above in such counter queries.

If you are using the SQL layer, then you can use arbitrary SQL expressions in the update statement:

    conn.execute(tags.update(tags.c.tag_id == 5).values(count=tags.c.count + 1))

The ORM Query object also has an update method:

    session.query(Tag).filter_by(tag_id=5).update({&#39;count&#39;: Tag.count + 1})

The ORM version is smart enough to also update the count attribute on the object itself if it&#39;s in the session.


I got here following a tutorial for [FastAPI][1], [SQLAlchemy][2] and [databases][3] (async). After various tries I finally got it working with following code in my crud.py / control layer.

```python
async def inc_counter():
    query = counters.select(counters.c.id==1)
    current_val = await database.fetch_val(query=query, column=1)
    query = counters.update().where(counters.c.id==1).values(counter=current_val+1).returning(counters.c.counter)
    return await database.execute(query=query)
``` 

My table looks like this:

```python
counters = Table(&#39;counters&#39;, metadata,
    Column(&#39;id&#39;, Integer, primary_key=True),
    Column(&#39;counter&#39;, Integer)
)
```


  [1]: https://fastapi.tiangolo.com/advanced/async-sql-databases/
  [2]: https://www.sqlalchemy.org/
  [3]: https://www.encode.io/databases/

Eclipse is adding @Override annotations when I implement methods of an interface.  Eclipse seems to have no problem with this.  And our automated build process from Cruise Control seems to have no problem with this.  But when I build from the command-line, with ant running javac, I get this error:

    [javac] C:\path\project\src\com\us\MyClass.java:70: method does not override a method from its superclass
    [javac]     @Override
    [javac]      ^
    [javac] 1 error

Eclipse is running under Java 1.6.  Cruise Control is running Java 1.5.  My ant build fails regardless of which version of Java I use.

Why is javac failing on @Override annotation

I was wondering if there were statistics functions built into math libraries that are part of the standard C++ libraries like cmath. If not, can you guys recommend a good stats library that would have a cumulative normal distribution function? Thanks in advance.

More specifically, I am looking to use/create a cumulative distribution function.

Cumulative Normal Distribution Function in C/C++

Suppose I have table `tags` which has a field `count` that indicates how many `items` have been tagged with the given tag.

How do I increase this counter in SQLAlchemy after I add a new item with an existing tag?

With plain SQL I would do the following:

    INSERT INTO `items` VALUES (...)
    UPDATE `tags` SET count=count+1 WHERE tag_id=5

But how do I express `count=count+1` in SQLAlchemy?

How to increase a counter in SQLAlchemy

Suppose I have table <code>tags</code> which has a field <code>count</code> that indicates how many <code>items</code> have been tagged with the given tag.
How do I increase this counter in SQLAlchemy after I add a new item with an existing tag?
With plain SQL I would do the following:
<pre><code class="hljs language-sql">INSERT INTO `items` VALUES (...)
UPDATE `tags` SET count=count+1 WHERE tag_id=5
</code></pre>
But how do I express <code>count=count+1</code> in SQLAlchemy?

Much of my programming background is in Java, and I&#39;m still doing most of my programming in Java. However, I&#39;m starting to learn Python for some side projects at work, and I&#39;d like to learn it as independent of my Java background as possible - i.e. I don&#39;t want to just program Java in Python. What are some things I should look out for?

A quick example - when looking through the Python tutorial, I came across the fact that defaulted mutable parameters of a function (such as a list) are persisted (remembered from call to call). This was counter-intuitive to me as a Java programmer and hard to get my head around. (See [here][1] and [here][2] if you don&#39;t understand the example.)

Someone also provided me with [this][3] list, which I found helpful, but short. Anyone have any other examples of how a Java programmer might tend to misuse Python...? Or things a Java programmer would falsely assume or have trouble understanding?

**Edit**: Ok, a brief overview of the reasons addressed by the article I linked to to prevent duplicates in the answers (as suggested by Bill the Lizard). (Please let me know if I make a mistake in phrasing, I&#39;ve only *just* started with Python so I may not understand all the concepts fully. And a disclaimer - these are going to be *very* brief, so if you don&#39;t understand what it&#39;s getting at check out the link.)

 - A static method in Java does not translate to a Python classmethod
 - A switch statement in Java translates to a hash table in Python
 - Don&#39;t use XML
 - Getters and setters are evil (hey, I&#39;m just quoting :) )
 - Code duplication is often a necessary evil in Java (e.g. method overloading), but not in Python

(And if you find this question at all interesting, check out the link anyway. :) It&#39;s quite good.)

  [1]: https://stackoverflow.com/questions/1132941/least-astonishment-in-python-the-mutable-default-argument
  [2]: https://stackoverflow.com/questions/2335160/what-is-the-scope-of-a-defaulted-parameter-in-python
  [3]: http://dirtsimple.org/2004/12/python-is-not-java.html

As a Java programmer learning Python, what should I look out for?

I am trying to use `str.encode()` but I get

    &gt;&gt;&gt; &quot;hello&quot;.encode(hex)
    Traceback (most recent call last):
      File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt;
    TypeError: must be string, not builtin_function_or_method

I have tried a bunch of variations and they seem to all work in Python 2.5.2, so what do I need to do to get them to work in Python 3.1?

Python 3.1.1 string to hex

By default, in Django-admin there is Users, Groups, and Sites apps. How can I remove Groups and Sites?

I tried to remove `admin.autodiscover()` from root urls. Then, when I added something like `admin.site.register(User, UserAdmin)` somewhere in my app models I got an `AlreadyRegistered` exception (this is fairly right - models users already registered in django.contrib.auth).


Remove default apps from Django-admin

I&#39;m looking to do this:

    class Place(models.Model):
       name = models.CharField(max_length=20)
       rating = models.DecimalField()
    
    class LongNamedRestaurant(Place):  # Subclassing `Place`.
       name = models.CharField(max_length=255)  # Notice, I&#39;m overriding `Place.name` to give it a longer length.
       food_type = models.CharField(max_length=25)


This is the version I would like to use (although I&#39;m open to any suggestion):
http://docs.djangoproject.com/en/dev/topics/db/models/#id7

Is this supported in Django? If not, is there a way to achieve similar results?

In Django - Model Inheritance - Does it allow you to override a parent model&#39;s attribute?

Is there a relatively quick program out there to accomplish at least the basics of this? Just a few regexes? I&#39;m willing to do some manual conversion, but this is a pretty big set of scripts.

Conversion from JavaScript to Python code?

I&#39;ve been trying to figure out how to iterate over the list of columns defined in a SQLAlchemy model. I want it for writing some serialization and copy methods to a couple of models. I can&#39;t just iterate over the `obj.__dict__` since it contains a lot of SA specific items. 

Anyone know of a way to just get the `id` and `desc` names from the following?

    class JobStatus(Base):
        __tablename__ = &#39;jobstatus&#39;
    
        id = Column(Integer, primary_key=True)
        desc = Column(Unicode(20))

In this small case I could easily create a:

    def logme(self):
        return {&#39;id&#39;: self.id, &#39;desc&#39;: self.desc}

but I&#39;d prefer something that auto-generates the `dict` (for larger objects).


method of iterating over sqlalchemy model&#39;s defined columns?

I want to get an object from the database if it already exists (based on provided parameters) or create it if it does not.

Django&#39;s [`get_or_create`](https://docs.djangoproject.com/en/1.10/ref/models/querysets/#get-or-create) (or [source](https://github.com/django/django/blob/master/django/db/models/query.py#L462)) does this.  Is there an equivalent shortcut in SQLAlchemy?

I&#39;m currently writing it out explicitly like this:

    def get_or_create_instrument(session, serial_number):
        instrument = session.query(Instrument).filter_by(serial_number=serial_number).first()
        if instrument:
            return instrument
        else:
            instrument = Instrument(serial_number)
            session.add(instrument)
            return instrument

Does SQLAlchemy have an equivalent of Django&#39;s get_or_create?

I am trying to get all rows from a table.

In controller I have: 

&lt;!-- language: lang-python --&gt;

    meta.Session.query(User).all()

The result is `[, ]`, but I have 2 rows in this table.

I use this model for the table:

&lt;!-- language: lang-python --&gt;

    import hashlib
    import sqlalchemy as sa
    from sqlalchemy import orm
    
    from allsun.model import meta
    
    t_user =  sa.Table(&quot;users&quot;,meta.metadata,autoload=True)
    
    class Duplicat(Exception):
        pass
    class LoginExistsException(Exception):
        pass
    class EmailExistsException(Exception):
        pass

And next, in the same file:

&lt;!-- language: lang-python --&gt;

    class User(object):
        def loginExists(self):
            try:
                meta.Session
                    .query(User)
                    .filter(User.login==self.login)
                    .one()
            except orm.exc.NoResultFound:
                pass
            else:
                raise LoginExistsException()
    
        def emailExists(self):
            try:
                meta
                    .Session
                    .query(User)
                    .filter(User.email==self.email)
                    .one()
            except orm.exc.NoResultFound:
                pass
            else:
                raise EmailExistsException()
    
    
        def save(self):
            meta.Session.begin()
            meta.Session.save(self)
            try:
                meta.Session.commit()
            except sa.exc.IntegrityError:
                raise Duplicat()
    
    orm.mapper(User, t_user)


How can I select all rows with sqlalchemy?

I want to map a Tag entity using declarative method with SQLAlchemy. A tag can have a parent (another Tag).

I have:

    class Tag(Base):
        __tablename__ = &#39;tag&#39;
        
        id = Column(Integer, primary_key=True)
        label = Column(String)
        
        def __init__(self, label, parentTag=None):
            self.label = label

How can I add the &quot;parent&quot; relationship?



SQLAlchemy - Mapping self-referential relationship as one to many (declarative form)

I&#39;m reading about sqlalchemy and I saw following code:

    employees_table = Table(&#39;employees&#39;, metadata,
        Column(&#39;employee_id&#39;, Integer, primary_key=True),
        Column(&#39;name&#39;, String(50)),
        Column(&#39;manager_data&#39;, String(50)),
        Column(&#39;engineer_info&#39;, String(50)),
        Column(&#39;type&#39;, String(20), nullable=False)
    )

    employee_mapper = mapper(Employee, employees_table, \
        polymorphic_on=employees_table.c.type, polymorphic_identity=&#39;employee&#39;)
    manager_mapper = mapper(Manager, inherits=employee_mapper, polymorphic_identity=&#39;manager&#39;)
    engineer_mapper = mapper(Engineer, inherits=employee_mapper, polymorphic_identity=&#39;engineer&#39;)


Should I make &#39;type&#39; an int, with constants in a library?  Or should I make just make type an enum?

Content Type	Original Author	Original Content on Stackoverflow
Question	bodacydo	View Question on Stackoverflow
Solution 1 - Python	tux21b	View Answer on Stackoverflow
Solution 2 - Python	Ants Aasma	View Answer on Stackoverflow
Solution 3 - Python	Leon	View Answer on Stackoverflow

How to increase a counter in SQLAlchemy

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Solution 3 - Python

Cumulative Normal Distribution Function in C/C++

Why is javac failing on @Override annotation

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