I want to build a Python function that calculates,

![alt text][1]

and would like to name my summation function Σ. In a similar fashion, would like to use Π for product, and so on. I was wondering if there was a way to name a python function in this fashion?

    def Σ (..):
     ..
     ..

That is, does Python support unicode identifiers, and if so, could someone provide an example for it?

Thanks!

  [1]: https://1.bp.blogspot.com/_mGF7Mo1o9b4/SlT2s9H7g_I/AAAAAAAAABE/RYgqR4C3XSM/s400/entropy


----------

Original motivation for this was a piece of Clojure code I saw today that looks like,

    (defn entropy [X]
          (* -1 (Σ [i X] (* (p i) (log (p i))))))

where Σ is a macro defined as,

    (defmacro Σ
        ... )

and I thought that was pretty cool.


----------

BTW, to address a couple of comments about readability - with a lot of stats/ML code for instance, being able to compose operations with symbols would be really helpful. (Especially for really complex integrals et al)

    φ(z) = ∫(N(x|0,1,1), -∞, z)

vs

    Phi(z) = integral(N(x|0,1,1), -inf, z)

or even just the lambda character for lambda()!


Unicode identifiers in Python?

One of my kids is taking Java in high school and had this on one of his tests:

&gt; Which of the following is a valid identifier in Java?
&gt;
&gt; a.  `123java`  
    b.  `main`  
    c.  `java1234`  
    d.  `{abce`  
    e.  `)whoot`  

He answered **b** and got it wrong.  

I looked at the question and argued that `main` *is* a valid identifier and that it should have been right.  

We took a look at the Java [spec][1] for identifiers and it reinforced that point.  We also wrote a sample program that had a variable called `main`, as well as a method.  He created a written rebuttal that included the Java documentation reference, the test program and the teacher ignored it and says the answer is still incorrect.

Is `main` a valid identifier?  



  [1]: https://docs.oracle.com/javase/specs/jls/se8/html/jls-3.html

Is main a valid Java identifier?

Hope this question wasn&#39;t asked before. Does anyone know the character limit for domain names?
For example if I write this:

    CREATE DOMAIN d_complement_activite_etablissement AS character varying

it will create a domain with the name:

    d_complement_activite_etabliss

(Yeah, I know how to count, but I want some more info on the subject).

Is there a command that can change this maximum length? Is this length the same for other names (columns, tables etc)?

Maximum characters in labels (table names, columns etc)

Why am I getting this exception?

    package com.domain.idea;

    import javax.persistence.CascadeType;
    import javax.persistence.Entity;
    import javax.persistence.FetchType;
    import javax.persistence.JoinColumn;
    import javax.persistence.OneToOne;
    import javax.persistence.Table;
    
    import org.hibernate.annotations.AccessType;
    
    /**
     * object model for the view [InvestmentReturn].[vMAE_MFE]
     */
    @Entity
    @Table(name=&quot;vMAE_MFE&quot;, schema=&quot;InvestmentReturn&quot;)
    @AccessType(&quot;field&quot;)
    public class MAE_MFEView
    {
    	/**
    	 * trade property is a SuggestdTradeRecommendation object
    	 */
    	@OneToOne(fetch = FetchType.LAZY , cascade = { CascadeType.PERSIST })
    	@JoinColumn(name = &quot;suggestedTradeRecommendationID&quot;)
    	private SuggestedTradeRecommendation trade;
    	
    	/**
    	 * Most Adeverse Excursion value
    	 */
    	private int MAE;

    	public int getMAE()
     	{
    		return MAE;
    	}
    	
     	/**
    	 * Most Favorable Excursion value
    	 */
    	private int MFE;
    	
    	public int getMFE()
    	{
    		return MFE;
    	}
    	
    	/**
    	 * @return trade property
    	 * see #trade
    	 */
    	public SuggestedTradeRecommendation getTrade()
    	{
    		return trade;
    	}
    }

Update: I&#39;ve changed my code to look like this:  

    package com.domain.idea;
   
    import javax.persistence.CascadeType;
    import javax.persistence.FetchType;
    import javax.persistence.Entity;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.OneToOne;
    import javax.persistence.Table;
    
    import org.hibernate.annotations.AccessType;
    
    /**
     * object model for the view [InvestmentReturn].[vMAE_MFE]
     */
    @Entity
    @Table(name=&quot;vMAE_MFE&quot;, schema=&quot;InvestmentReturn&quot;)
    @AccessType(&quot;field&quot;)
    public class MAE_MFEView
    {
    	/**
    	 * trade property is a SuggestdTradeRecommendation object
    	 */
    	@Id
    	@OneToOne(fetch = FetchType.LAZY , cascade = { CascadeType.PERSIST })
    	@JoinColumn(name = &quot;suggestedTradeRecommendationID&quot;)
    	private SuggestedTradeRecommendation trade;
    	
    	/**
    	 * Most Adeverse Excursion value
    	 */
    	private int MAE;

     	public int getMAE()
     	{
    		return MAE;
     	}
     	
     	/**
	     * Most Favorable Excursion value
     	 */
    	private int MFE;
    	
    	public int getMFE()
    	{
     		return MFE;
    	}
    	
    	/**
    	 * @return trade property
    	 * see #trade
    	 */
    	public SuggestedTradeRecommendation getTrade()
    	{
    		return trade;
    	}
    }

but now I&#39;m getting this exception:  

    Caused by: org.hibernate.MappingException: Could not determine type for: com.domain.idea.SuggestedTradeRecommendation, at table: vMAE_MFE, for columns: [org.hibernate.mapping.Column(trade)]
    	at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:292)
    	at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:276)
    	at org.hibernate.mapping.RootClass.validate(RootClass.java:216)
    	at org.hibernate.cfg.Configuration.validate(Configuration.java:1135)
    	at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1320)
    	at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:867)
    	at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:669)
    	... 145 more

Hibernate throws org.hibernate.AnnotationException: No identifier specified for entity: com..domain.idea.MAE_MFEView

I am reading for SCJP and I have a question regarding this line:

&gt; Identifiers must start with a letter, a currency character ($), or a
&gt; connecting character such as the underscore ( _ ). Identifiers cannot
&gt; start with a number!

It states that a valid identifier name can start with a connecting character **such as** underscore. I thought underscores were the only valid option? What other *connecting characters* are there?

What are &quot;connecting characters&quot; in Java identifiers?

I have a db table say, `persons` in Postgres handed down by another team that has a column name say, `&quot;first_Name&quot;`. Now am trying to use PG commander to query this table on this column-name.

    select * from persons where first_Name=&quot;xyz&quot;;

And it just returns

&gt;  ERROR:  column &quot;first_Name&quot; does not exist

Not sure if I am doing something silly or is there a workaround to this problem that I am missing?

Are PostgreSQL column names case-sensitive?

It seems PostgreSQL does not allow to create a database table named &#39;user&#39;. But MySQL will allow to create such a table.

Is that because it is a key word? But Hibernate cannot identify any issue (even if we set the PostgreSQLDialect).

Cannot create a database table named &#39;user&#39; in PostgreSQL

Recently started digging in to JSON, and I&#39;m currently trying to use a number as &quot;identifier&quot;, which doesn&#39;t work out too well. `foo:&quot;bar&quot;` works fine, while `0:&quot;bar&quot;` doesn&#39;t. 

    var Game = {
    	status: [
                    {
                        0:&quot;val&quot;,
                        1:&quot;val&quot;,
                        2:&quot;val&quot;
                    },
                    {
                        0:&quot;val&quot;,
                        1:&quot;val&quot;,
                        2:&quot;val&quot;
                    }
               ]
    }
    
    alert(Game.status[0].0);

Is there any way to do it the following way? Something like `Game.status[0].0` Would make my life way easier. Of course there&#39;s other ways around it, but this way is preferred.

Using number as &quot;index&quot; (JSON)

I want to pass a table name as a parameter in a Postgres function. I tried this code:

    CREATE OR REPLACE FUNCTION some_f(param character varying) RETURNS integer 
    AS $$
        BEGIN
    	IF EXISTS (select * from quote_ident($1) where quote_ident($1).id=1) THEN
    	 return 1;
    	END IF;
        return 0;
        END;
    $$ LANGUAGE plpgsql;
    
    select some_f(&#39;table_name&#39;);

And I got this:

    ERROR:  syntax error at or near &quot;.&quot;
    LINE 4: ...elect * from quote_ident($1) where quote_ident($1).id=1)...
                                                                 ^
    
    ********** Error **********
    
    ERROR: syntax error at or near &quot;.&quot;

And here is the error I got when changed to this `select * from quote_ident($1) tab where tab.id=1`:

    ERROR:  column tab.id does not exist
    LINE 1: ...T EXISTS (select * from quote_ident($1) tab where tab.id...

Probably, `quote_ident($1)` works, because without the `where quote_ident($1).id=1` part I get `1`, which means something is selected. Why may the first `quote_ident($1)` work and the second one not at the same time? And how could this be solved?

Table name as a PostgreSQL function parameter

What&#39;s the Hi/Lo algorithm?

I&#39;ve found this in the [NHibernate][1] documentation (it&#39;s one method to generate unique keys, section 5.1.4.2), but I haven&#39;t found a good explanation of how it works.

I know that Nhibernate handles it, and I don&#39;t need to know the inside, but I&#39;m just curious.

  [1]: http://en.wikipedia.org/wiki/NHibernate


What&#39;s the Hi/Lo algorithm?

Variables in Python are just pointers, as far as I know.

Based on this rule, I can assume that the result for this code snippet:

    i = 5
    j = i
    j = 3
    print(i)

would be `3`.

But I got an unexpected result for me, and it was `5`.

Moreover, my Python book does cover this example:

    i = [1,2,3]
    j = i
    i[0] = 5
    print(j)

The result would be `[5,2,3]`.

What am I understanding wrong?




Are Python variables pointers? Or else, what are they?

&lt;pre&gt;
Caused by: org.springframework.orm.hibernate3.HibernateSystemException: ids for this class must be manually assigned before calling save(): com.rfid.model.Role; nested exception is org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): com.rfid.model.Role
	at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:676)
	at org.springframework.orm.hibernate3.HibernateAccessor.convertHibernateAccessException(HibernateAccessor.java:412)
	at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:424)
	at org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:374)
	at org.springframework.orm.hibernate3.HibernateTemplate.saveOrUpdate(HibernateTemplate.java:748)
	at com.wfos.engine.wrapper.domain.impl.WrapperImpl.save(WrapperImpl.java:159)
	... 47 more
    Caused by: org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): com.rfid.model.Role
	at org.hibernate.id.Assigned.generate(Assigned.java:53)
	at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:121)
	at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)
	at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)
	at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:117)
	at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
	at org.hibernate.impl.SessionImpl.fireSaveOrUpdate(SessionImpl.java:685)
	at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:677)
	at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:673)
	at org.springframework.orm.hibernate3.HibernateTemplate$16.doInHibernate(HibernateTemplate.java:751)
	at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:419)
	... 50 more
    WARN [21:14:21] (CommonsLoggingOutput.java:59): - --Erroring: batchId[1] message[java.lang.reflect.UndeclaredThrowableException]
&lt;/pre&gt;


My class is like this:

    @Entity
    @javax.persistence.Table(name=&quot;Role&quot;)
    @Table(appliesTo = &quot;Role&quot;)
    public class Role {
	
	@Id  
	@Column(name=&quot;U_id&quot;)
	public String U_id;
	  
	public String U_pwd;
	 
	public String U_account;
	  
	public String U_mode;
	 
	public String U_status;


	public String getU_pwd() {
		return U_pwd;
	}

	public void setU_pwd(String u_pwd) {
		U_pwd = u_pwd;
	}

	public String getU_account() {
		return U_account;
	}

	public void setU_account(String u_account) {
		U_account = u_account;
	}

	public String getU_id() {
		return U_id;
	}

	public void setU_id(String u_id) {
		U_id = u_id;
	}

	public String getU_mode() {
		return U_mode;
	}

	public void setU_mode(String u_mode) {
		U_mode = u_mode;
	}

	public String getU_status() {
		return U_status;
	}

	public void setU_status(String u_status) {
		U_status = u_status;
	}
	
    }

Hibernate error: ids for this class must be manually assigned before calling save():

I&#39;m recently starting to pick up C++ and the SFML library, and I was wondering if I defined a Sprite on a file appropriately called &quot;player.cpp&quot; how would I call it on my main loop located at &quot;main.cpp&quot;?

Here is my code (Be aware that this is SFML 2.0, not 1.6!).

main.cpp

    #include &quot;stdafx.h&quot;
    #include &lt;SFML/Graphics.hpp&gt;
    #include &quot;player.cpp&quot;

    int main()
    {
        sf::RenderWindow window(sf::VideoMode(800, 600), &quot;Skylords - Alpha v1&quot;);

        while (window.isOpen())
        {
            sf::Event event;
            while (window.pollEvent(event))
            {
                if (event.type == sf::Event::Closed)
                    window.close();
            }

            window.clear();
            window.draw();
            window.display();
        }

        return 0;
    }

player.cpp

    #include &quot;stdafx.h&quot;
    #include &lt;SFML/Graphics.hpp&gt;

    int playerSprite(){
        sf::Texture Texture;
        if(!Texture.loadFromFile(&quot;player.png&quot;)){
            return 1;
        }
        sf::Sprite Sprite;
        Sprite.setTexture(Texture);
        return 0;
    }

Where I need help is in the `main.cpp` where it says `window.draw();` in my draw code. In that parenthesis, there should be the name of the Sprite that I want to load onto the screen. As far as I&#39;ve searched, and tried by guessing, I have not succeeded into making that draw function work with my sprite on the other file.
I feel like I&#39;m missing something big, and very obvious (on either files), but then again, every pro was once a newb.

How to call on a function found on another file?

I fetch data from Google&#39;s AdWords website which has multiple elements with the same `id`.

Could you please explain why the following 3 queries doesn&#39;t result with the same answer (2)?

[Live Demo][1]

HTML:

    &lt;div&gt;
        &lt;span id=&quot;a&quot;&gt;1&lt;/span&gt;
        &lt;span id=&quot;a&quot;&gt;2&lt;/span&gt;
        &lt;span&gt;3&lt;/span&gt;
    &lt;/div&gt;

JS:

    $(function() {
        var w = $(&quot;div&quot;);
        console.log($(&quot;#a&quot;).length);            // 1 - Why?
        console.log($(&quot;body #a&quot;).length);       // 2
        console.log($(&quot;#a&quot;, w).length);         // 2
    });


  [1]: http://jsfiddle.net/P2j3f/1/

How does jQuery work when there are multiple elements with the same ID value?

Can someone please explain the exact meaning of having single and double leading underscores before an object&#39;s name in Python, and the difference between both?

Also, does that meaning stay the same regardless of whether the object in question is a variable, a function, a method, etc.?

What is the meaning of single and double underscore before an object name?

I am developing an iOS app which calls web-service for login and at that time i send login credentials to web server along with vendor identifier (identifierForVendor),to identify device uniquely for those credentials.So user can have only one device and one credential.

I got identifierForVendor with 

    NSString *uuid = [[UIDevice currentDevice] identifierForVendor].UUIDString

This identifier will then store in database of web server and also in device database.Next time when user opens application and will try to download data from web server firstly local identifierForVendor on users device will compare with identifier stored on web server.

Problem occurs when user uninstall app and reinstall it, I found that identifierForVendor is changed. So user cannot proceed further.

I read apple documentation [UIDevice Documentation][1]


  [1]: https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIDevice_Class/Reference/UIDevice.html#//apple_ref/doc/uid/TP40006902-CH3-SW49

As mention there, if all app from same vendor uninstalls from device then at time of new installation of any app from that vendor will take new identifierForVendor. 

So how to deal with this in my case ?

How to preserve identifierForVendor in ios after uninstalling ios app on device?

I am trying to create a table that was dropped previously.  

But when I do the `CREATE TABLE A ..`. I am getting below error: 

&gt; Relation &#39;A&#39; already exists.

I verified doing `SELECT * FROM A`, but then I got another error: 

&gt; Relation &#39;A&#39; does not exists.

I already tried to find it in `\dS+` listing all relations, and it is not there.  
To complicate this, I have tested this by creating this table in another database and I got the same error. I am thinking that could be an error when this table was dropped. Any ideas?

Here is the code: I&#39;m using a generated code from Power SQL. I have the same error without using the sequence. It just works when I change the name and in this case I can not do that.

    CREATE SEQUENCE csd_relationship_csd_relationship_id_seq;
    CREATE TABLE csd_relationship (
        csd_relationship_id INTEGER NOT NULL DEFAULT nextval(&#39;csd_relationship_csd_relationship_id_seq&#39;::regclass),  
        type_id INTEGER NOT NULL,
        object_id INTEGER NOT NULL,
        CONSTRAINT csd_relationship PRIMARY KEY (csd_relationship_id)
    );

PostgreSQL Error: Relation already exists

We&#39;re going to provide our clients with a tool that (among other things) creates a new SQL Server database, and I want to be able to do basic validation on the database name they provide. SQL Server&#39;s documentation explains what characters are valid in a database name. However, the documentation is apparently incorrect, because I can successfully create databases whose names violate the documented rules.

According to SQL Server&#39;s documentation for &lt;a href=&quot;http://msdn.microsoft.com/en-us/library/ms176061.aspx&quot;&gt;CREATE DATABASE&lt;/a&gt;, database names must comply with the rules for identifiers; and the rules for &lt;a href=&quot;http://msdn.microsoft.com/en-us/library/ms175874.aspx&quot;&gt;identifiers&lt;/a&gt; depend on the database compatibility level. When the compatibility level is 100 (which, according to SQL Server Management Studio, means &quot;SQL Server 2008&quot;), the name must start with a Unicode letter, `_`, `@`, or `#`; followed by one or more letters, numbers, `@`, `$`, `#`, or `_`. The documentation clearly states that embedded spaces or special characters are not allowed.

This flies in the face of the available evidence, because I can use SQL Server Management Studio to create a database whose name is `This &amp; That | &quot;Other&quot;` -- which not only contains embedded spaces (explicitly forbidden), but contains special characters (`|`, `&quot;`) that aren&#39;t even valid in a filename. I checked, and the database&#39;s compatibility level is indeed &quot;SQL Server 2008 (100)&quot;, even though its name is documented to be invalid at that compatibility level.

Heck, I can even do `CREATE DATABASE &quot; &quot;` (yes, that&#39;s a single space), which proves that the first character does *not* have to be a letter, underscore, at sign, or pound sign.

So I guess my question is, what characters **are** valid in an SQL Server database name? Are there any documented rules that are consistent with SQL Server&#39;s actual behavior?

All Identifier Solutions on Gang of Coders

Total of 18 Identifier Solutions