    sum(item[&#39;gold&#39;] for item in myList)

If you&#39;re memory conscious:

    sum(item[&#39;gold&#39;] for item in example_list)


If you&#39;re extremely time conscious:

    sum([item[&#39;gold&#39;] for item in example_list])

In most cases just use the generator expression, as the performance increase is only noticeable on a very large dataset/very hot code path.

See [this answer][1] for an explanation of why you should avoid using map.

See [this answer][2] for some real-world timing comparisons of list comprehension vs generator expressions.
    


  [1]: https://stackoverflow.com/questions/1247486/python-list-comprehension-vs-map/1247490#1247490
  [2]: https://stackoverflow.com/questions/5889611/one-liner-to-determine-if-dictionary-values-are-all-empty-lists-or-not/5889662#5889662

If you prefer `map`, this works too:

     import operator
     total_gold = sum(map(operator.itemgetter(&#39;gold&#39;),example_list))

But I think the generator posted by g.d.d.c is significantly better.  This answer is really just to point out the existence of `operator.itemgetter`.

``` python
from collections import Counter
from functools import reduce
from operator import add

sum_dict = reduce(add, (map(Counter, example_list)))
# Counter({&#39;points&#39;: 700, &#39;gold&#39;: 4330})
total_gold = sum_dict[&#39;gold&#39;]
```


    example_list = [
        {&#39;points&#39;: 400, &#39;gold&#39;: 2480},
        {&#39;points&#39;: 100, &#39;gold&#39;: 610},
        {&#39;points&#39;: 100, &#39;gold&#39;: 620},
        {&#39;points&#39;: 100, &#39;gold&#39;: 620}
    ]
    
    result = np.sum([x[&#39;gold&#39;] for x in example_list])
    
    
    print(result)

output

     4330

I have a number of records that I need to insert into multiple tables. Every other column will be a constant.

Poor pseudo code below - this is what I want to do:

    create table #temp_buildings
    (
    	building_id varchar(20)
    )
    insert into #temp_buildings (building_id) VALUES (&#39;11070&#39;)
    insert into #temp_buildings (building_id) VALUES (&#39;11071&#39;)
    insert into #temp_buildings (building_id) VALUES (&#39;20570&#39;)
    insert into #temp_buildings (building_id) VALUES (&#39;21570&#39;)
    insert into #temp_buildings (building_id) VALUES (&#39;22570&#39;)
    
    insert into property.portfolio_property_xref
            ( portfolio_id ,
              building_id ,
              created_date ,
              last_modified_date
            )
    values
            ( 
    			34 ,
    			(
    				select	building_id
    				from	#temp_buildings
    			) ,
    			getdate() ,
    			null
            )


**Intent:** Perform an insert into property.portfolio_property_xref for each record on #temp_buildings

I think I could do this with a cursor - but believe this would be horribly slow. As this exercise will be repeatable in future I&#39;d rather tackle this in a faster method but I&#39;m unsure how. Any feedback would be appreciated!

Perform insert for each row taken from a select?

A method I am calling in [run()][1] in a class that implements [Runnable][2]) is designed to be throwing an exception.

But the Java compiler won&#39;t let me do that and suggests that I surround it with try/catch.

The problem is that by surrounding it with a try/catch I make *that particular* [run()][3] useless. I *do* want to throw that exception.

If I specify `throws` for [run()][4] itself, the compiler complains that `Exception is not compatible with throws clause in Runnable.run()`.

Ordinarily I&#39;m totally fine with not letting  [run()][3] throw an exception. But I have unique situation in which I must have that functionality.

How to I work around this limitation?


  [1]: http://developer.android.com/reference/java/lang/Runnable.html#run%28%29
  [2]: http://developer.android.com/reference/java/lang/Runnable.html
  [3]: http://developer.android.com/reference/java/lang/Runnable.html#run%28%29
  [4]: http://developer.android.com/reference/java/lang/Runnable.html#run%28%29

Is there a way to make Runnable&#39;s run() throw an exception?

I have got pretty simple list:

    example_list = [
        {&#39;points&#39;: 400, &#39;gold&#39;: 2480},
        {&#39;points&#39;: 100, &#39;gold&#39;: 610},
        {&#39;points&#39;: 100, &#39;gold&#39;: 620},
        {&#39;points&#39;: 100, &#39;gold&#39;: 620}
    ]

How can I sum all *gold* values? I&#39;m looking for nice oneliner.

Now I&#39;m using this code (but it&#39;s not the best solution):

    total_gold = 0
    for item in example_list:
        total_gold += example_list[&quot;gold&quot;]

Python - sum values in dictionary

I have got pretty simple list:
<pre><code class="hljs language-ini">example_list = [
 {'points': 400, 'gold': 2480},
 {'points': 100, 'gold': 610},
 {'points': 100, 'gold': 620},
 {'points': 100, 'gold': 620}
]
</code></pre>
How can I sum all gold values? I'm looking for nice oneliner.
Now I'm using this code (but it's not the best solution):
<pre><code class="hljs language-ini">total_gold = 0
for item in example_list:
 total_gold += example_list["gold"]
</code></pre>

Please excuse my confusion here but I have read the documentation regarding the seek() function in python (after having to use it) and although it helped me I am still a bit confused on the actual meaning of what it does, any explanations are much appreciated, thank you.

seek() function?

I am going to convert a Django QuerySet to a pandas `DataFrame` as follows:

    qs = SomeModel.objects.select_related().filter(date__year=2012)
    q = qs.values(&#39;date&#39;, &#39;OtherField&#39;)
    df = pd.DataFrame.from_records(q)

It works, but is there a more efficient way?

Converting Django QuerySet to pandas DataFrame

I have a Bottle webserver module with the following line:

    from foobar.formtools import auto_process_form_insert

And the `foobar.formtools` module contains this line:

    from foobar.webserver import redirect, redirect_back

Of course, both result in the following errors (respectively):

&gt; ImportError: cannot import name auto_process_form_insert  
&gt; ImportError: cannot import name redirect

Is it simply a fact that in Python two modules can&#39;t import each other and all module imports must be hierarchical in nature, or am I doing something wrong? Alternatively, is there a workaround short of placing all these nice functions in new modules?

Two Python modules require each other&#39;s contents - can that work?

I&#39;m using Python bindings to OpenCV 2.4 installed with following [instructions][1].

My problem is similar to [this one][2], but I need Windows machine solution.

Problem: when I try to use 

    cap = cv2.VideoCapture(0)
    print cap.grab()

it works fine, but the following code

    cap = cv2.VideoCapture(filename)
    print cap.grab()

always return False. 

Path to the file is correct, absolute and has no spaces.

I tried on two machines with Windows XP and Windows 7 with similar results. On Linux (Ubuntu) it works fine for me.


  [1]: http://opencvpython.blogspot.com/2012/05/install-opencv-in-windows-for-python.html
  [2]: https://stackoverflow.com/questions/11444926/videocapture-is-not-working-in-opencv-2-4-2

OpenCV 2.4 VideoCapture not working on Windows

To create Python virtual environments I use virtualenv and pip. The workflow is very simple:

    $ virtualenv project
    $ cd project
    $ . bin/activate
    $ pip install -r /path/to/requirements/req1.txt
    $ pip install -r /path/to/requirements/req2.txt

The number of different requirement files can grow enough to make handy to have a way to include them at once, so I&#39;d rather prefer to say:

    $ pip install -r /path/to/requirements/req1_req2.txt

with `req1_req2.txt` containing something like:

    include /path/to/requirements/req1.txt
    include /path/to/requirements/req2.txt

or otherwise:

    $ pip install -r /path/to/requirements/*.txt

None of that works and however much simple it could be, I can&#39;t figure out how to do what I want.

Any suggestion?

Split requirements files in pip

I have a list of passengers(object) where it has a differents properties..

    passenger.name
    passenger.age
    passenger.surname

And I want to sort this list by age criterion, how can i do this?

I know in a list of integer/string List.Sort() works, but if is an object list, i dont know if its possible to sort by the value of a object property!
    

Thanks.



Sort a List of Object in VB.NET

I have two lists with different objects in them.

    List&lt;Object1&gt; list1;
    List&lt;Object2&gt; list2;

I want to check if element from list1 exists in list2, based on specific attribute (Object1 and Object2 have (among others),  one mutual attribute (with type Long), named attributeSame).

right now, I do it like this:

    boolean found = false;
    for(Object1 object1 : list1){
       for(Object2 object2: list2){
           if(object1.getAttributeSame() == object2.getAttributeSame()){
               found = true;
               //also do something
           }
        }
        if(!found){
            //do something
        }
        found = false;
    }
But I think there is a better and faster way to do this :)
Can someone propose it?

Thanks!

Check if one list contains element from the other

In Python I have a list of elements `aList` and a list of indices `myIndices`. Is there any way I can retrieve all at once those items in `aList` having as indices the values in `myIndices`?

Example:

    &gt;&gt;&gt; aList = [&#39;a&#39;, &#39;b&#39;, &#39;c&#39;, &#39;d&#39;, &#39;e&#39;, &#39;f&#39;, &#39;g&#39;]
    &gt;&gt;&gt; myIndices = [0, 3, 4]
    &gt;&gt;&gt; aList.A_FUNCTION(myIndices)
    [&#39;a&#39;, &#39;d&#39;, &#39;e&#39;]

Python: filtering lists by indices

I was refactoring some old code of mine and came across of this:

    alist.sort(cmp_items)
    
    def cmp_items(a, b):
        if a.foo &gt; b.foo:
            return 1
        elif a.foo == b.foo:
            return 0
        else:
            return -1

The code works (and I wrote it some 3 years ago!) but I cannot find this thing documented anywhere in the Python docs and everybody uses `sorted()` to implement custom sorting. Can someone explain why this works?

Custom Python list sorting

I am using **BeautifulSoup** and parsing some HTMLs.

I&#39;m getting a certain data from each HTML *(using for loop)* and adding that data to a certain list.

The problem is, some of the HTMLs have different format *(and they don&#39;t have the data that I want in them)*.

So, I was trying to use exception handling and add value `null` to the list *(I should do this since the sequence of data is important.)*

For instance, I have a code like:

    soup = BeautifulSoup(links)
    dlist = soup.findAll(&#39;dd&#39;, &#39;title&#39;)
    # I&#39;m trying to find content between &lt;dd class=&#39;title&#39;&gt; and &lt;/dd&gt;
    gotdata = dlist[1]
    # and what i want is the 2nd content of those
    newlist.append(gotdata)
    # and I add that to a newlist

and some of the links don&#39;t have any `&lt;dd class=&#39;title&#39;&gt;`, so what I want to do is add string `null` to the list instead.

The error appears: 

    list index out of range.

What I have done tried is to add some lines like this:

    if not dlist[1]:  
       newlist.append(&#39;null&#39;)
       continue

But it doesn&#39;t work out. It still shows error:

    list index out of range.

What should I do about this? Should I use exception handling? or is there any easier way?

Any suggestions? Any help would be really great!

I want to exception handle &#39;list index out of range.&#39;

I have checked all of the other questions with the same error yet found no helpful solution =/

I have a dictionary of lists:

    d = {&#39;a&#39;: [1], &#39;b&#39;: [1, 2], &#39;c&#39;: [], &#39;d&#39;:[]}

in which some of the values are empty. At the end of creating these lists, I want to remove these empty lists before returning my dictionary. Current I am attempting to do this as follows:

    for i in d:
        if not d[i]:
            d.pop(i)

however, this is giving me the runtime error. I am aware that you cannot add/remove elements in a dictionary while iterating through it...what would be a way around this then?

How to avoid &quot;RuntimeError: dictionary changed size during iteration&quot; error?

I know that we can easily use *ng-repeat* for json objects or arrays like:

    &lt;div ng-repeat=&quot;user in users&quot;&gt;&lt;/div&gt;

but how can we use the ng-repeat for dictionaries, for example:

    var users = null;
    users[&quot;182982&quot;] = &quot;{...json-object...}&quot;;
    users[&quot;198784&quot;] = &quot;{...json-object...}&quot;;
    users[&quot;119827&quot;] = &quot;{...json-object...}&quot;;

I want to use that with users dictionary:

    &lt;div ng-repeat=&quot;user in users&quot;&gt;&lt;/div&gt;

Is it possible?. If yes, how can I do it in AngularJs?


Example for my question:
In C# we define dictionaries like:

    Dictionary&lt;key,value&gt; dict = new Dictionary&lt;key,value&gt;();
    
    //and then we can search for values, without knowing the keys
    foreach(var val in dict.Values)
    {
    }

Is there a build-in function that returns the values from a dictionary like in c#?


How to use ng-repeat for dictionaries in AngularJs?

I have a dict and would like to remove all the keys for which there are empty value strings.

    metadata = {u&#39;Composite:PreviewImage&#39;: u&#39;(Binary data 101973 bytes)&#39;,
                u&#39;EXIF:CFAPattern2&#39;: u&#39;&#39;}

What is the best way to do this?



Efficient way to remove keys with empty strings from a dict

How can I get the dictionary value by a key on a function?

My function code (and the command I try doesn&#39;t work):

    static void XML_Array(Dictionary&lt;string, string&gt; Data_Array)
    {
        String xmlfile = Data_Array.TryGetValue(&quot;XML_File&quot;, out value);
    }

My button code:

    private void button2_Click(object sender, EventArgs e)
    {
        Dictionary&lt;string, string&gt; Data_Array = new Dictionary&lt;string, string&gt;();
        Data_Array.Add(&quot;XML_File&quot;, &quot;Settings.xml&quot;);

        XML_Array(Data_Array);
    }

I want on the `XML_Array` function the variable to be:

    string xmlfile = &quot;Settings.xml&quot;:






Get dictionary value by key

Given a dictionary `{ k1: v1, k2: v2 ... }` I want to get `{ k1: f(v1), k2: f(v2) ... }` provided I pass a function `f`.

Is there any such built in function? Or do I have to do

    dict([(k, f(v)) for (k, v) in my_dictionary.iteritems()])

Ideally I would just write

    my_dictionary.map_values(f)

or

    my_dictionary.mutate_values_with(f)

That is, it doesn&#39;t matter to me if the original dictionary is mutated or a copy is created.

Content Type	Original Author	Original Content on Stackoverflow
Question	Mateusz Jagiełło	View Question on Stackoverflow
Solution 1 - Python	g.d.d.c	View Answer on Stackoverflow
Solution 2 - Python	Ben Burns	View Answer on Stackoverflow
Solution 3 - Python	mgilson	View Answer on Stackoverflow
Solution 4 - Python	xmduhan	View Answer on Stackoverflow
Solution 5 - Python	Golden Lion	View Answer on Stackoverflow

Python - sum values in dictionary

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Solution 3 - Python

Solution 4 - Python

Solution 5 - Python

Is there a way to make Runnable's run() throw an exception?

Perform insert for each row taken from a select?

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