You can make a numpy array unwriteable:

    a = np.arange(10)
    a.flags.writeable = False
    a[0] = 1
    # Gives: ValueError: assignment destination is read-only


Also see the discussion in this thread:

http://mail.scipy.org/pipermail/numpy-discussion/2008-December/039274.html

and the documentation:

http://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.flags.html

I have a subclass of Array at this gist: https://gist.github.com/sfaleron/9791418d7023a9985bb803170c5d93d8

It makes a copy of its argument and marks that as read-only, so you should only be able to shoot yourself in the foot if you are very deliberate about it. My immediate need was for it to be hashable, so I could use them in sets, so that works too. It isn&#39;t a lot of code, but about 70% of the lines are for testing, so I won&#39;t post it directly.

Note that it&#39;s not a drop-in replacement; it won&#39;t accept any keyword args like a normal Array constructor. Instances will behave like Arrays, though.

Setting the flag directly didn&#39;t work for me, but using [`ndarray.setflags`](https://numpy.org/doc/stable/reference/generated/numpy.ndarray.setflags.html) did work:

```python
a = np.arange(10)
a.setflags(write=False)
a[0] = 1  # ValueError
```

Is there a way to determine if a MKMapView was dragged around?

I want to get the center location every time a user drags the map using `CLLocationCoordinate2D centre = [locationMap centerCoordinate];` but I&#39;d need a delegate method or something that fires as soon as the user navigates around with the map.

Thanks in advance

determine if MKMapView was dragged/moved

How can I get UTC offset from time zone name in python?

For example: I have `Asia/Jerusalem` and I want to get `+0200`

Get UTC offset from time zone name in python

Is there a simple way to create an immutable NumPy array?

If one has to derive a class from `ndarray` to do this, what&#39;s the minimum set of methods that one has to override to achieve immutability?

Immutable numpy array?

<p>Is there a simple way to create an immutable NumPy array?</p>
<p>If one has to derive a class from <code>ndarray</code> to do this, what's the minimum set of methods that one has to override to achieve immutability?</p>


What is the difference between filter with multiple arguments and chain filter in django?

difference between filter with multiple arguments and chain filter in django

How can I retrieve a list of tasks in a queue that are yet to be processed?

Retrieve list of tasks in a queue in Celery

The piece of code that I have looks some what like this:

    glbl_array = # a 3 Gb array
    
    def my_func( args, def_param = glbl_array):
        #do stuff on args and def_param

    if __name__ == &#39;__main__&#39;:
      pool = Pool(processes=4)
      pool.map(my_func, range(1000))

Is there a way to make sure (or encourage) that the different processes does not get a copy of glbl_array but shares it. If there is no way to stop the copy I will go with a memmapped array, but my access patterns are not very regular, so I expect memmapped arrays to be slower. The above seemed like the first thing to try. This is on Linux. I just wanted some advice from Stackoverflow and do not want to annoy the sysadmin. Do you think it will help if the the second parameter is a genuine immutable object like `glbl_array.tostring()`.

Is shared readonly data copied to different processes for multiprocessing?

How can I ignore `.pyc` files in git?

If I put it in `.gitignore` it doesn&#39;t work. I need them to be untracked and not checked for commits.

Ignore .pyc files in git repository

Very often I need to create dicts that differ one from another by an item or two. Here is what I usually do:

    setup1 = {&#39;param1&#39;: val1, 
                &#39;param2&#39;: val2,
                &#39;param3&#39;: val3,
                &#39;param4&#39;: val4,
                &#39;paramN&#39;: valN}
                
    setup2 = copy.deepcopy(dict(setup1))
    setup2.update({&#39;param1&#39;: val10, 
                       &#39;param2&#39;: val20})
                       
                       
The fact that there is a point in the program at which `setup2` is an identical copy of `setup1` makes me nervous, as I&#39;m afraid that at some point of the program life the two lines might get separated, which is a slippery slope towards too many bugs. 

Ideally I would like to be able to complete this action in a single line of code (something like this):


    setup2 = dict(setup1).merge({&#39;param1&#39;: val10, 
                            &#39;param2&#39;: val20})



Of course, I can use semicolon to squeeze two commands into  one physical line, but this looks pretty ugly to me. Are there other options?  
                          
        

How to copy a dict and modify it in one line of code

I&#39;m getting up to speed with C++0x, and testing things out with g++ 4.6

I just tried the following code, thinking it would work, but it doesn&#39;t compile. I get the error:

`incompatible types in assignment of ‘std::initializer_list&lt;const int&gt;’ to ‘const int [2]’`


    struct Foo
      {
        int const data[2];

        Foo(std::initializer_list&lt;int const&gt;&amp; ini)
        : data(ini)
        {}
      };

    Foo f = {1,3};


How do I initialize a member array with an initializer_list?

What does `ArrayIndexOutOfBoundsException` mean and how do I get rid of it? 

Here is a code sample that triggers the exception:

    String[] names = { &quot;tom&quot;, &quot;bob&quot;, &quot;harry&quot; };
    for (int i = 0; i &lt;= names.length; i++) {
        System.out.println(names[i]);
    }


What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it?

I can not export an array from a bash script to another bash script like this:

    export myArray[0]=&quot;Hello&quot;
    export myArray[1]=&quot;World&quot;

When I write like this there are no problem:

    export myArray=(&quot;Hello&quot; &quot;World&quot;)

For several reasons I need to initialize my array into multiple lines. Do you have any solution?

Exporting an array in bash script

What is the difference between the two functions in C?

    void f1(double a[]) {
       //...
    }

    void f2(double *a) {
       //...
    }

If I were to call the functions on a substantially long array, would these two functions behave differently, would they take more space on the stack?

Difference between passing array and array pointer into function in C

Is there a built-in function to get all members of array 1 which do not exist in array 2?  
I know how to do it programatically, only wondering if there is a built-in function that does the same. So please, no code examples.

Opposite of array_intersect?

I am playing with `numpy` and digging through documentation and I have come across some magic. Namely I am talking about `numpy.where()`:

    &gt;&gt;&gt; x = np.arange(9.).reshape(3, 3)
    &gt;&gt;&gt; np.where( x &gt; 5 )
    (array([2, 2, 2]), array([0, 1, 2]))

How do they achieve internally that you are able to pass something like `x &gt; 5` into a method? I guess it has something to do with `__gt__` but I am looking for a detailed explanation.

How does python numpy.where() work?

I would like to get data from a single contour of evenly spaced 2D data (an image-like data).

Based on the example found in a similar question: https://stackoverflow.com/q/1560424/429795 

    &gt;&gt;&gt; import matplotlib.pyplot as plt
    &gt;&gt;&gt; x = [1,2,3,4]
    &gt;&gt;&gt; y = [1,2,3,4]
    &gt;&gt;&gt; m = [[15,14,13,12],[14,12,10,8],[13,10,7,4],[12,8,4,0]]
    &gt;&gt;&gt; cs = plt.contour(x,y,m, [9.5])
    &gt;&gt;&gt; cs.collections[0].get_paths()

The result of this call into `cs.collections[0].get_paths()` is:

    [Path([[ 4.          1.625     ]
     [ 3.25        2.        ]
     [ 3.          2.16666667]
     [ 2.16666667  3.        ]
     [ 2.          3.25      ]
     [ 1.625       4.        ]], None)]

Based on the plots, this result makes sense and appears to be collection of (y,x) pairs for the contour line.  

Other than manually looping over this return value, extracting the coordinates and assembling arrays for the line, are there better ways to get data back from a `matplotlib.path` object?  Are there pitfalls to be aware of when extracting data from a `matplotlib.path`?
 
Alternatively, are there alternatives within `matplotlib` or better yet `numpy`/`scipy` to do a similar thing?  Ideal thing would be to get a high resolution vector of (x,y) pairs describing the line, which could be used for further analysis, as in general my datasets are not a small or simple as the example above.


matplotlib - extracting data from contour lines

In the help resource for the multivariate normal sampling function in SciPy, they give the following example:

    x,y = np.random.multivariate_normal(mean,cov,5000).T

My question is rather basic: what does the final .T actually do?

Thanks a lot, I know it is fairly simple, but it is hard to look in Google for &quot;.T&quot;.

Syntax in Python (.T)

I am waiting for another developer to finish a piece of code that will return an np array of shape (100,2000) with values of either -1,0, or 1.

In the meantime, I want to randomly create an array of the same characteristics so I can get a head start on my development and testing. The thing is that I want this randomly created array to be the same each time, so that I&#39;m not testing against an array that keeps changing its value each time I re-run my process.

I can create my array like this, but is there a way to create it so that it&#39;s the same each time. I can pickle the object and unpickle it, but wondering if there&#39;s another way.

    r = np.random.randint(3, size=(100, 2000)) - 1


Consistently create same random numpy array

I know this is probably very stupid, but a lot of places claim that the Integer class in Java is immutable, yet the following code:

    Integer a=3;
    Integer b=3;
    a+=b;
    System.out.println(a);
Executes without any trouble giving the (expected) result 6. So effectively the value of a has changed. Doesn&#39;t that mean Integer is mutable?
Secondary question and a little offtopic: &quot;Immutable classes do not need copy constructors&quot;. Anyone care to explain why?


Is Integer Immutable

I know that value types should be immutable, but that&#39;s just a suggestion, not a rule, right?
So why can&#39;t I do something like this:

    struct MyStruct
    {
        public string Name { get; set; }
    }

     public class Program
    {
        static void Main(string[] args)
        {
            MyStruct[] array = new MyStruct[] { new MyStruct { Name = &quot;1&quot; }, new MyStruct { Name = &quot;2&quot; } };
            foreach (var item in array)
            {
                item.Name = &quot;3&quot;;
            }
            //for (int i = 0; i &lt; array.Length; i++)
            //{
            //    array[i].Name = &quot;3&quot;;
            //}

            Console.ReadLine();
        }
    }

The foreach loop in the code doesn&#39;t compile while the commented for loop works fine. The error message:

&gt; Cannot modify members of &#39;item&#39; because it is a &#39;foreach iteration variable&#39;

Why is that?


In C#, why can&#39;t I modify the member of a value type instance in a foreach loop?

Hi how to set `R G B` values in `System.Drawing.Color.G` ?

which is like `System.Drawing.Color.G=255;` is not allowed because its read only 


    Property or indexer &#39;System.Drawing.Color.G&#39; cannot be assigned toit is read only

i just need to create a `Color` Object by assigning custom `R G B` values 



Set System.Drawing.Color values

Is this a proper way to declare immutable structs?

    public struct Pair
    {
        public readonly int x;
        public readonly int y;
        
        // Constructor and stuff
    }

I can&#39;t think of why this would run into problems, but I just wanted to ask to make sure.

In this example, I used ints. What if I used a class instead, but that class is also immutable, like so? That should work fine too, right?

    public struct Pair
    {
        public readonly (immutableClass) x;
        public readonly (immutableClass) y;
        
        // Constructor and stuff
    }

(Aside: I understand that using Properties is more generalizable and allows changing, but this struct is intended literally to just store two values. I&#39;m just interested in the immutability question here.)

Does using public readonly fields for immutable structs work?

I have this API function:

    public ResultEnum DoSomeAction(string a, string b, DateTime c, OtherEnum d, 
         string e, string f, out Guid code)

I don&#39;t like it. Because parameter order becomes unnecessarily significant. It becomes harder to add new fields. It&#39;s harder to see what&#39;s being passed around. It&#39;s harder to refactor method into smaller parts because it creates another overhead of passing all the parameters in sub functions. Code is harder to read. 

I came up with the most obvious idea: have an object encapsulating the data and pass it around instead of passing each parameter one by one. Here is what I came up with:

    public class DoSomeActionParameters
    {
        public string A;
        public string B;
        public DateTime C;
        public OtherEnum D;
        public string E;
        public string F;        
    }

That reduced my API declaration to:

    public ResultEnum DoSomeAction(DoSomeActionParameters parameters, out Guid code)

Nice. Looks very innocent but we actually introduced a huge change: we introduced mutability. Because what we previously had been doing was actually to pass an anonymous immutable object: function parameters on stack. Now we created a new class which is very mutable. We created the ability to manipulate the state of the **caller**. That sucks. Now I want my object immutable, what do I do?

    public class DoSomeActionParameters
    {
        public string A { get; private set; }
        public string B { get; private set; }
        public DateTime C { get; private set; }
        public OtherEnum D { get; private set; }
        public string E { get; private set; }
        public string F { get; private set; }        
        
        public DoSomeActionParameters(string a, string b, DateTime c, OtherEnum d, 
         string e, string f)
        {
            this.A = a;
            this.B = b;
            // ... tears erased the text here
        }
    }

As you can see I actually re-created my original problem: too many parameters. It&#39;s obvious that that&#39;s not the way to go. What am I going to do? The last option to achieve such immutability is to use a &quot;readonly&quot; struct like this:

    public struct DoSomeActionParameters
    {
        public readonly string A;
        public readonly string B;
        public readonly DateTime C;
        public readonly OtherEnum D;
        public readonly string E;
        public readonly string F;        
    }

That allows us to avoid constructors with too many parameters and achieve immutability. Actually it fixes all the problems (parameter ordering etc). Yet:

- Everybody (including FXCop &amp; Jon Skeet) agree that [exposing public fields are bad][1].
- Eric Lippert et al say [relying on readonly fields for immutability is a lie][2].

That&#39;s when I got confused and decided to write this question: What&#39;s the most straightforward way in C# to avoid &quot;too many parameters&quot; problem without introducing mutability? Is it possible to use a readonly struct for that purpose and yet not have a bad API design?

**CLARIFICATIONS:**

- Please assume there is no violation of single responsibiltiy principle. In my original case the function just writes given parameters to a single DB record.
- I&#39;m not seeking a specific solution to the given function. I&#39;m seeking a generalized approach to such problems. I&#39;m specifically interested in solving &quot;too many parameters&quot; problem without introducing mutability or a terrible design.

**UPDATE**

The answers provided here have different advantages/disadvantages. Therefore I&#39;d like to convert this to a community wiki. I think each answer with code sample and Pros/Cons would make a good guide for similar problems in the future. I&#39;m now trying to find out how to do it.

  [1]: http://csharpindepth.com/Articles/Chapter8/PropertiesMatter.aspx
  [2]: http://www.bluebytesoftware.com/blog/2010/07/01/WhenIsAReadonlyFieldNotReadonly.aspx

How to avoid &quot;too many parameters&quot; problem in API design?

I&#39;ve been working on creating a class and suddenly a thought came to my mind of what is the difference between the two codes:

    public readonly string ProductLocation;

AND

    public string ProductLocation
    {
         get;
         private set;
    }

Can you guys give me idea when to use the following better. thanks.

Which is better between a readonly modifier and a private setter?

How can I make a model completely read-only in the admin interface? It&#39;s for a kind of log table, where I&#39;m using the admin features to search, sort, filter etc, but there is no need to modify the log.

In case this looks like a duplicate, here&#39;s *not* what I&#39;m trying to do:

 * I&#39;m not looking for readonly *fields* (even making every field readonly would still let you create new records)
 * I&#39;m not looking to create a readonly *user*: every user should be readonly.



Readonly models in Django admin interface?

I want to make readOnly with EditorFor in edit page.

I tried to put readonly and disabled as:

    &lt;div class=&quot;editor-field&quot;&gt;
            @Html.EditorFor(model =&gt; model.userName, new { disabled = &quot;disabled&quot;, @readonly = &quot;readonly&quot; })
        &lt;/div&gt;

However, it does not work. How can I make to disable edit this field?

Thank you.

MVC3 EditorFor readOnly

I need to expose an Entity Framework Data Context to 3rd party plugins. The purpose is to allow these plugins to fetch data only and not to let them issue inserts, updates or deletes or any other database modification commands. Hence how can I make a data context or entity readonly.

How to make Entity Framework Data Context Readonly

I&#39;m making a form. And on one `input` tag is an `OnClick` event handler, which is opening a popup, where you can choose some stuff, and then it autofills the `input` tag.

That input tag is also `readonly`, so only right data will be entered.

This is the code of the `input` tag:

    &lt;input type=&quot;text&quot; name=&quot;formAfterRederict&quot; id=&quot;formAfterRederict&quot; size=&quot;50&quot; required readonly=&quot;readonly&quot; OnClick=&quot;choose_le_page();&quot;  /&gt;

But the `required` attribute isn&#39;t working in Chrome. But the field is required.

Does anybody know how I can make it work?

Content Type	Original Author	Original Content on Stackoverflow
Question	NPE	View Question on Stackoverflow
Solution 1 - Python	JoshAdel	View Answer on Stackoverflow
Solution 2 - Python	sfaleron	View Answer on Stackoverflow
Solution 3 - Python	Kris	View Answer on Stackoverflow

Immutable numpy array?

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Get UTC offset from time zone name in python

determine if MKMapView was dragged/moved

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