Your `debut` and `fin` values are floating point values, not integers, because `taille` is a float.

Make those values integers instead:

    item = plateau[int(debut):int(fin)]

Alternatively, make `taille` an integer:

    taille = int(sqrt(len(plateau)))


When you slice a list the slices must be integers. 

Take notice of the type of your indices variables or of possible operations you are performing while slicing

    a = [1, 2, 3, 4]
    b = a[:len(a)/2] # Will give your error because in python division ALWAYS returns float
    c = a[:len(a)//2] # Correct answer

I know this isn&#39;t exactly a good response to your question in particular, but it&#39;s a broader answer.



My Rails app uses Devise for authentication. It has a sister iOS app, and users can log in to the iOS app using the same credentials that they use for the web app. So I need some kind of API for authentication.

Lots of similar questions on here point to [this tutorial](http://jessewolgamott.com/blog/2012/01/19/the-one-with-a-json-api-login-using-devise/), but it seems to be out-of-date, as the `token_authenticatable` module has since been removed from Devise and some of the lines throw errors. (I&#39;m using Devise 3.2.2.) I&#39;ve attempted to roll my own based on that tutorial (and [this one](http://danrodriguez.me/post/54352441822/)), but I&#39;m not 100% confident in it - I feel like there may be something I&#39;ve misunderstood or missed.

Firstly, following the advice of [this gist](https://gist.github.com/josevalim/fb706b1e933ef01e4fb6), I added an `authentication_token` text attribute to my `users` table, and the following to `user.rb`:

    before_save :ensure_authentication_token
    
    def ensure_authentication_token
      if authentication_token.blank?
        self.authentication_token = generate_authentication_token
      end
    end
     
    private
      
      def generate_authentication_token
        loop do
          token = Devise.friendly_token
          break token unless User.find_by(authentication_token: token)
        end
      end

Then I have the following controllers:

**api_controller.rb**


    class ApiController &lt; ApplicationController
      respond_to :json
      skip_before_filter :authenticate_user!
    
      protected
    
      def user_params
        params[:user].permit(:email, :password, :password_confirmation)
      end
    end

(Note that my `application_controller` has the line `before_filter :authenticate_user!`.)


**api/sessions_controller.rb**


    class Api::SessionsController &lt; Devise::RegistrationsController
      prepend_before_filter :require_no_authentication, :only =&gt; [:create ]
      
      before_filter :ensure_params_exist
     
      respond_to :json
    
      skip_before_filter :verify_authenticity_token
      
      def create
        build_resource
        resource = User.find_for_database_authentication(
          email: params[:user][:email]
        )
        return invalid_login_attempt unless resource
     
        if resource.valid_password?(params[:user][:password])
          sign_in(&quot;user&quot;, resource)
          render json: {
            success: true,
            auth_token: resource.authentication_token,
            email: resource.email
          }
          return
        end
        invalid_login_attempt
      end
      
      def destroy
        sign_out(resource_name)
      end
     
      protected
    
        def ensure_params_exist
          return unless params[:user].blank?
          render json: {
            success: false,
            message: &quot;missing user parameter&quot;
          }, status: 422
        end
       
        def invalid_login_attempt
          warden.custom_failure!
          render json: {
            success: false,
            message: &quot;Error with your login or password&quot;
          }, status: 401
        end
    end


**api/registrations_controller.rb**


    class Api::RegistrationsController &lt; ApiController
      skip_before_filter :verify_authenticity_token

      def create
        user = User.new(user_params)
        if user.save
          render(
            json: Jbuilder.encode do |j|
              j.success true
              j.email user.email
              j.auth_token user.authentication_token
            end,
            status: 201
          )
          return
        else
          warden.custom_failure!
          render json: user.errors, status: 422
        end
      end
    end

And in **config/routes.rb**:


      namespace :api, defaults: { format: &quot;json&quot; } do
        devise_for :users
      end


I&#39;m out of my depth a bit and I&#39;m sure there&#39;s something here that my future self will look back on and cringe (there usually is). Some iffy parts:

**Firstly**, you&#39;ll notice that `Api::SessionsController` inherits from `Devise::RegistrationsController` whereas `Api::RegistrationsController` inherits from `ApiController` (I also have some other controllers such as `Api::EventsController &lt; ApiController` which deal with more standard REST stuff for my other models and don&#39;t have much contact with Devise.) This is a pretty ugly arrangement, but I couldn&#39;t figure out another way of getting access the methods I need in `Api::RegistrationsController`. The tutorial I linked to above has the line `include Devise::Controllers::InternalHelpers`, but this module seems to have been removed in more recent versions of Devise.

**Secondly**, I&#39;ve disabled CSRF protection with the line `skip_before_filter :verify_authentication_token`. I have my doubts about whether this is a good idea - I see a lot of [conflicting](https://stackoverflow.com/questions/7600347/rails-api-design-without-disabling-csrf-protection) or [hard to understand](https://stackoverflow.com/questions/11008469/are-json-web-services-vulnerable-to-csrf-attacks) advice about whether JSON APIs are vulnerable to CSRF attacks - but adding that line was the only way I could get the damn thing to work.

**Thirdly**, I want to make sure I understand how authentication works once a user has signed in. Say I have an API call `GET /api/friends` which returns a list of the current user&#39;s friends. As I understand it, the iOS app would have to get the user&#39;s `authentication_token` from the database (which is a fixed value for each user that never changes??), then submit it as a param along with every request, e.g. `GET /api/friends?authentication_token=abcdefgh1234`, then my `Api::FriendsController` could do something like `User.find_by(authentication_token: params[:authentication_token])` to get the current_user. Is it really this simple, or am I missing something?

So for anyone who&#39;s managed to read all the way to the end of this mammoth question, thanks for your time! To summarise:

1. **Is this login system secure?** Or is there something I&#39;ve overlooked or misunderstood, e.g. when it comes to CSRF attacks?
2. **Is my understanding of how to authenticate requests once users are signed in correct?** (See &quot;thirdly...&quot; above.)
3. **Is there any way this code can be cleaned up or made nicer?** Particularly the ugly design of having one controller inherit from `Devise::RegistrationsController` and the others from `ApiController`.

Thanks!


Is this Rails JSON authentication API (using Devise) secure?

I have a question about inner joins with multiple on values.
I did build my code like this in laravel.

    public function scopeShops($query) {
        return $query-&gt;join(&#39;kg_shops&#39;, function($join)
        {
            $join-&gt;on(&#39;kg_shops.id&#39;, &#39;=&#39;, &#39;kg_feeds.shop_id&#39;);
            // $join-&gt;on(&#39;kg_shops.active&#39;, &#39;=&#39;, &quot;1&quot;); // WRONG
            // EDITED ON 28-04-2014
            $join-&gt;on(&#39;kg_shops.active&#39;, &#39;=&#39;, DB::raw(&quot;1&quot;));
 
        });
    }

Only problem is, it gives this outcome:

    Column not found: 1054 Unknown column &#39;1&#39; in &#39;on clause&#39; (SQL: select `kg_feeds`.* from `kg_feeds` inner join `kg_shops` on `kg_shops`.`id` = `kg_  
      feeds`.`shop_id` and `kg_shops`.`active` = `1`) (Bindings: array (                                                                                        )) 

As you can see, the multiple conditions in the join go fine, but it thinks the `1` is a column instead of a string. Is this even possible, or do I have to fix it in the where.

Thanks in advance! 


Laravel Eloquent inner join with multiple conditions

I&#39;m trying something with Python. I want to slice a list (plateau) in several list (L[i]) but I have the following error message:

      File &quot;C:\Users\adescamp\Skycraper\skycraper.py&quot;, line 20, in &lt;module&gt;
        item = plateau[debut:fin]
    TypeError: slice indices must be integers or None or have an __index__ method

The concerned line is the one with `item = plateau[debut:fin]`

    from math import sqrt

    plateau = [2, 3, 1, 4, 1, 4, 2, 3, 4, 1, 3, 2, 3, 2, 4, 1]

    taille = sqrt(len(plateau))

    # Division en lignes
    L = []
    i = 1
    while i &lt; taille:
        fin = i * taille
        debut = fin - taille
        item = plateau[debut:fin]
        L.append(item)
        i += 1


Slice indices must be integers or None or have __index__ method

I'm trying something with Python. I want to slice a list (plateau) in several list (L[i]) but I have the following error message:
<pre><code class="hljs language-arduino"> File "C:\Users\adescamp\Skycraper\skycraper.py", line 20, in &#x3C;module>
 item = plateau[debut:fin]
TypeError: slice indices must be integers or None or have an __index__ method
</code></pre>
The concerned line is the one with <code>item = plateau[debut:fin]</code>
<pre><code class="hljs language-ini">from math import sqrt

plateau = [2, 3, 1, 4, 1, 4, 2, 3, 4, 1, 3, 2, 3, 2, 4, 1]

taille = sqrt(len(plateau))

# Division en lignes
L = []
i = 1
while i &#x3C; taille:
 fin = i * taille
 debut = fin - taille
 item = plateau[debut:fin]
 L.append(item)
 i += 1
</code></pre>

I&#39;m trying to integrate PostgreSQL and SQLAlchemy but SQLAlchemy.create_all() is not creating any tables from my models.

My code:
    &lt;!-- language: python --&gt;

    from flask import Flask
    from flask.ext.sqlalchemy import SQLAlchemy
    
    app = Flask(__name__)
    app.config[&#39;SQLALCHEMY_DATABASE_URI&#39;] = &#39;postgresql+psycopg2://login:pass@localhost/flask_app&#39;
    db = SQLAlchemy(app)
    db.create_all()
    db.session.commit()
    
    class User(db.Model):
        id = db.Column(db.Integer, primary_key=True)
        username = db.Column(db.String(80), unique=True)
        email = db.Column(db.String(120), unique=True)
    
        def __init__(self, username, email):
            self.username = username
            self.email = email
    
        def __repr__(self):
            return &#39;&lt;User %r&gt;&#39; % self.username
    
    admin = User(&#39;admin&#39;, &#39;admin@example.com&#39;)
    guest = User(&#39;guest&#39;, &#39;guest@example.com&#39;)
    db.session.add(admin)
    db.session.add(guest)
    db.session.commit()
    users = User.query.all()
    print users        

    
But I get this error: `sqlalchemy.exc.ProgrammingError: (ProgrammingError) relation &quot;user&quot; does not exist`

How can I fix this?

SQLAlchemy create_all() does not create tables

I&#39;m trying to login a website for some scraping using Python and requests library, I am trying the following (which doesn&#39;t work):


	import requests
	headers = {&#39;User-Agent&#39;: &#39;Mozilla/5.0&#39;}
	payload = {&#39;username&#39;:&#39;niceusername&#39;,&#39;password&#39;:&#39;123456&#39;}

	In [12]: r = requests.post(&#39;https://admin.example.com/login.php&#39;,headers=headers,data=payload)

But nada, getting a redirect to the login page. Do I need to open a session? am I doing a wrong POST request, do I need to load the cookies?
or does session does that automatically?
I am lost here, some help and explanations are needed.

The website I&#39;m trying to login is php, do I need to &quot;capture the set-cookie and set the cookie header&quot;? if so I have no idea how to do it.
The webpage is a form with the following (if it helps):
input :username&#39; &#39;password&#39;
&#39;id&#39;:&#39;myform&#39;, &#39;action&#39;:&quot;login.php

Some extra information, maybe you can see what I&#39;m missing here..

	In [13]: r.headers
	Out[13]: CaseInsensitiveDict({&#39;content-encoding&#39;: &#39;gzip&#39;, &#39;transfer-encoding&#39;: &#39;chunked&#39;,
	 &#39;set-cookie&#39;: &#39;PHPSESSID=v233mnt4malhed55lrpc5bp8o1; path=/&#39;,
	  &#39;expires&#39;: &#39;Thu, 19 Nov 1981 08:52:00 GMT&#39;, &#39;vary&#39;: &#39;Accept-Encoding&#39;, &#39;server&#39;: &#39;nginx&#39;,
	   &#39;connection&#39;: &#39;keep-alive&#39;, &#39;pragma&#39;: &#39;no-cache&#39;,
	    &#39;cache-control&#39;: &#39;no-store, no-cache, must-revalidate, post-check=0, pre-check=0&#39;,
	     &#39;date&#39;: &#39;Tue, 24 Dec 2013 10:50:44 GMT&#39;, &#39;content-type&#39;: &#39;text/html&#39;})

	In [14]: r.cookies
	Out[14]: &lt;&lt;class &#39;requests.cookies.RequestsCookieJar&#39;&gt;[Cookie(version=0, name=&#39;PHPSESSID&#39;,
	 value=&#39;v233mnt4malhed55lrpc5bp8o1&#39;, port=None, port_specified=False, domain=&#39;admin.example.com&#39;,
	  domain_specified=False, domain_initial_dot=False, path=&#39;/&#39;, path_specified=True, secure=False,
	   expires=None, discard=True, comment=None, comment_url=None, rest={}, rfc2109=False)]&gt;

I would really appreciate the help, thanks!

update, with answer thanks to atupal:

        import requests

	headers = {&#39;User-Agent&#39;: &#39;Mozilla/5.0&#39;}
	payload = {&#39;username&#39;:&#39;usr&#39;,&#39;pass&#39;:&#39;123&#39;}
	link    = &#39;https://admin.example.com/login.php&#39;
	session = requests.Session()
	resp    = session.get(link,headers=headers)
	# did this for first to get the cookies from the page, stored them with next line:
	cookies = requests.utils.cookiejar_from_dict(requests.utils.dict_from_cookiejar(session.cookies))
	resp    = session.post(link,headers=headers,data=payload,cookies =cookies)
	#used firebug to check POST data, password, was actually &#39;pass&#39;, under &#39;net&#39; in param.  
	#and to move forward from here after is:
	session.get(link)


Python : Trying to POST form using requests

The [python style guide][1] suggests to group imports like this:

&gt; Imports should be grouped in the following order:
&gt;
&gt;    1. standard library imports
&gt;    2. related third party imports
&gt;    3. local application/library specific imports

However, it does not mention anything how the two different ways of imports should be laid out:

    from foo import bar
    import foo

There are multiple ways to sort them (let&#39;s assume all those import belong to the same group):

* first `from..import`, then `import`

        from g import gg
        from x import xx
        import abc
        import def
        import x

* first `import`, then `from..import`

        import abc
        import def
        import x
        from g import gg
        from x import xx

- alphabetic order by module name, ignoring the kind of import

        import abc
        import def
        from g import gg
        import x
        from xx import xx

PEP8 does not mention the preferred order for this and the &quot;cleanup imports&quot; features some IDEs have probably just do whatever the developer of that feature preferred.

**I&#39;m looking for another PEP clarifying this or a relevant comment/email from the [BDFL][2]** (or another Python core developer). *Please don&#39;t post subjective answers stating your own preference.*


  [1]: http://www.python.org/dev/peps/pep-0008/#imports
  [2]: http://en.wikipedia.org/wiki/Guido_van_Rossum

What&#39;s the correct way to sort Python `import x` and `from x import y` statements?

I have a Numpy array consisting of a list of lists, representing a two-dimensional array with row labels and column names as shown below:

    data = array([[&#39;&#39;,&#39;Col1&#39;,&#39;Col2&#39;],[&#39;Row1&#39;,1,2],[&#39;Row2&#39;,3,4]])

I&#39;d like the resulting DataFrame to have Row1 and Row2 as index values, and Col1, Col2 as header values

I can specify the index as follows:

    df = pd.DataFrame(data,index=data[:,0]),
however I am unsure how to best assign column headers.


Creating a Pandas DataFrame from a Numpy array: How do I specify the index column and column headers?

I see people are running setups like Nginx + Gunicorn + Flask.

Can someone explain what is the benefit of having Gunicorn in front of Flask? Why not just run Flask alone? Doesn&#39;t it consume more resources having Gunicorn + Flask running? Is Gunicorn able to reboot the Flask instance when it fails to respond?

What&#39;s also the purpose of having nginx on top of gunicorn? Isn&#39;t gunicorn enough? Again, more resources being spent?

What benefit is added by using Gunicorn + Nginx + Flask?

What is the Go way for extracting the last element of a slice?

    var slice []int
    
    slice = append(slice, 2)
    slice = append(slice, 7)
    
    slice[len(slice)-1:][0] // Retrieves the last element

The solution above works, but seems awkward.

How to get the last element of a slice?

What is a slice in Swift and how does it differ from an array?

From the documentation, the type signature of subscript(Range&lt;Int&gt;) is:

    subscript(Range&lt;Int&gt;) -&gt; Slice&lt;T&gt;

Why not return another `Array&lt;T&gt;` rather than a `Slice&lt;T&gt;`?

It looks like I can concatenate a slice with an array:

    var list = [&quot;hello&quot;, &quot;world&quot;]
    var slice: Array&lt;String&gt; = [] + list[0..list.count]

But this yields the error:

&gt; could not find an overload for &#39;subscript&#39; that accepts the supplied
&gt; arguments

    var list = [&quot;hello&quot;, &quot;world&quot;]
    var slice: Array&lt;String&gt; = list[0..list.count]

What is a slice?

What is a slice in Swift?

In Go, what is the difference between `var s []int` and `s := make([]int, 0)`? 

I find that both works, but which one is better?

Declare slice or make slice?

We can easily do that with maps:

    item, ok := myMap[&quot;index&quot;]

But not with slices:
    
    item, ok := mySlice[3] // panic!

Surprised this wasn&#39;t asked before. Maybe I&#39;m on the wrong mental model with Go slices?

How to check if a slice has a given index in Go?

I often work with slices of structs. Here&#39;s an example for such a struct:

	type MyStruct struct {
		val1, val2, val3    int
		text1, text2, text3 string
		list                []SomeType
	}

So I define my slices as follows:

    []MyStruct

Let&#39;s say I have about a million elements in there and I&#39;m working heavily with the slice:

* I append new elements often. (The total number of elements is unknown.)
* I sort it every now and then.
* I also delete elements (although not as much as adding new elements).
* I read elements often and pass them around (as function arguments).
* The content of the elements themselves doesn&#39;t get changed.

My understanding is that this leads to a lot of shuffling around of the actual struct. The alternative is to create a slice of pointers to the struct:

    []*MyStruct

Now the structs remain where they are and we only deal with pointers which I assume have a smaller footprint and will therefore make my operations faster. But now I&#39;m giving the garbage collector a lot more work.

* Can you provide general guidelines of when to work with structs directly vs. when to work with pointers to structs?
* Should I worry about how much work I leave to the GC?
* Is the performance overhead of copying a struct vs. copying a pointer negligible?
* Maybe a million elements is not much. How does all of this change when the slice gets much bigger (but still fits in RAM, of course)?

Content Type	Original Author	Original Content on Stackoverflow
Question	DescampsAu	View Question on Stackoverflow
Solution 1 - Python	Martijn Pieters	View Answer on Stackoverflow
Solution 2 - Python	Lucas Sousa	View Answer on Stackoverflow

Slice indices must be integers or None or have index method

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Laravel Eloquent inner join with multiple conditions

Is this Rails JSON authentication API (using Devise) secure?

Attributions