Haskell in Tableau? Yes, you can!

Some time ago I posted about alternative TabPy implementation (AltTabPy – lightweight and straightforward alternative to TabPy) you can use with Tableau. Using that alternative solution is possible because AltTabPy implements TabPy API and Tableau Desktop or Server simply calls that API. So Tableau is not hardcoded to use TabPy.

But if alternative implementations are possible is it also possible to implement the API for something completely different than executing Python script… like another programming language?

Yes – it is possible and people actually do it. Here’s an example of how you can use Haskell scripts in Tableau calculations – https://databoss.starschema.net/tableau-external-services-api-adding-haskell-calculations/. The post explains step by step how to implement TabPy API in Haskell and how to use the server with Tableau. Very well written post indeed and highly recommended for reading. The project itself is available on GitHub – https://github.com/tfoldi/tc19-haskell-ext/.

With those two examples (and there are few more you can find) it should be possible to implement TabPy API for any programming language (Lua, SQL, JavaScript, etc.) or even a service (imagine receiving weather data for given coordinates and date/time).

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TabPy v0.9.0 released

As we getting closer to TabPy v1 being released (read here for more details – https://www.tableau.com/about/blog/2020/1/python-tableau-now-10) some bug fixes, documentation updates and code improvements are made. In the v0.9.0 release those are:

  • TabPy now works with Python 3.8.
  • Client.remove() method was added and now models (deployed functions) can be deleted with tabpy_tools.
  • Index page for running TabPy instance now shows the instance settings, deployed models and some useful links.
  • Bug fixes for Ctrl+C, query timeout, returning None or not returning value from a script, returning NaN in result.
  • Internals improvements for code quality, package size, test coverage.

To install this specific version run pip install tabpy==0.9.0 command.

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AltTabPy – lightweight and straightforward alternative to TabPy

Do you want to add some Python scripting to your Tableau visualization but struggle with How to Configure TabPy documentation? Take a look at AltTabPy – https://alttabpy.readthedocs.io/en/latest/index.html.

What TabPy is – Python script execution engine you can connect Tableau in the same way as you do for TabPy. Its installation and startup are extremely straightforward and simple, more details here – https://alttabpy.readthedocs.io/en/latest/getting_started.html#installing.

What TabPy is not – it does not support models (deployed functions), authentication, SSL, logging and other configuration and backward compatibility with older TabPy versions. Read here for more details on how AtlTabPy is different – https://alttabpy.readthedocs.io/en/latest/comparison.html.

AltTabPy is not supported by Tableau and is an independent project which (partially) implements TabPy API v1. The project itself is located on GitHub – https://github.com/innobi/AltTabPy.

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How to configure TabPy with authentication and use it in Tableau


In this post, I will demonstrate how to configure TabPy to require username and password, how to manage users for TabPy and how to connect from Tableau (both Desktop and Server) to TabPy with specifying credentials.

User Management for TabPy

After TabPy is installed (read Tableau Installation Instructions for how to install it) you can use tabpy-user command-line utility for adding and updating TabPy user accounts.

The utility itself supports a set of parameters such as a path to passwords file, operation, username and so on. Run tabpy-user -h to see all the parameters.

Adding a User

To add a user specify a username, a path to passwords file, password and add operation, e.g.:

c:\TabPy>tabpy-user add -u alice -f c:\TabPy\tabpypwd.txt -p P@ssw0rd
Parsing passwords file c:\TabPy\tabpypwd.txt...
Passwords file c:\TabPy\tabpypwd.txt not found
Adding username "alice"
Adding username "alice" with password "P@ssw0rd"...
Added username "alice" with password "P@ssw0rd"

In the example above the user alice with password P@ssw0rd was added to file c:\TabPy\tabpypwd.txt.

You can also let the utility generate a password for you simply skipping -p <Password> parameter:

c:\TabPy>tabpy-user add -u bob -f c:\TabPy\tabpypwd.txt
Parsing passwords file c:\TabPy\tabpypwd.txt...
Found username alice
Authentication is enabled
Generated password: ")7!f}dA_K=hrF7{x"
Adding username "bob"
Adding username "bob" with password ")7!f}dA_K=hrF7{x"...
Added username "bob" with password ")7!f}dA_K=hrF7{x"

In the example above new user bob was added to the same password file with password )7!f}dA_K=hrF7{x.

Updating User Password

It is possible to update the password for a user with update command, e.g.:

c:\TabPy>tabpy-user update -u alice -f c:\TabPy\tabpypwd.txt -p Secret_D0nt_Te11
Parsing passwords file c:\TabPy\tabpypwd.txt...
Found username alice
Found username bob
Authentication is enabled
Updating username "alice"
Updating username "alice" password  to "Secret_D0nt_Te11"

In this example alice‘s password was changed to Secret_D0nt_Te11.

What’s Inside Passwords File?

The password file is just a text file with user names and hashed passwords on each line. If you open the file you will see something like this:

alice edb6473a71775f48538c1cee15dc41269302b06b79260c70ce149d1b24a4192f764570702d5449fa2712c0a99d0db9216c1a452f07a3a3b44dca1b491cd7d516
bob 7716853bdc91132fe4bef86adaac0ae6fa9cf474c5b075e89880fcd21834d2bb16266eb65d0be0a8faa2ee48342708350b95af4af3caebbb8044f59341fcfab6

Those long codes are actually the hashes for the passwords. Instead of keeping passwords in plain text or encrypted form TabPy uses hashes. What it does is makes it impossible (rather incredibly expensive) to recover passwords from those hashes. If you wonder how the passwords are hashed – at the moment TabPy uses PBKDF2 method with 10000 iterations (https://en.wikipedia.org/wiki/PBKDF2).

Deleting a User

Since the password file is just a text file you can delete a user with any text editor simply deleting the whole line with the user name in it.

Configuring TabPy with Authentication

Now when you have the passwords file you can point TabPy to it so it knows to require credentials with all the requests to serve.

NOTE: any changes for the password file do not affect any running instances of TabPy – you will need to restart TabPy for the changes to take effect.

In previous post TabPy: modifying default configuration it was shown how to changes some (or all) TabPy configuration parameters with a config file. Let’s create a config file to turn on authentication as well. I am storing the following configuration in c:\TabPy\tabpy_auth.conf:

TABPY_PWD_FILE = c:\TabPy\tabpypwd.txt

As you can see the only configuration parameter I am modifying there is the password file path. In real-life scenarios, you will have logger settings, port, timeout and any other of the parameters documented at TabPy Custom Settings page.

Now let’s start TabPy with the config:

c:\TabPy>tabpy --config c:\TabPy\tabpy_auth.conf
DEBUG:tabpy.tabpy_server.app.app:Parameter TABPY_PWD_FILE set to "c:\TabPy\tabpypwd.txt" from config file or environment variable
INFO:tabpy.tabpy_server.app.util:Parsing passwords file c:\TabPy\tabpypwd.txt...
DEBUG:tabpy.tabpy_server.app.util:Found username alice
DEBUG:tabpy.tabpy_server.app.util:Found username bob
INFO:tabpy.tabpy_server.app.util:Authentication is enabled
INFO:tabpy.tabpy_server.app.app:Web service listening on port 9004

TabPy is running with authentication on!

Connecting from Tableau

For Tableau to communicate with TabPy when credentials are required you need to configure the product with username and password. As mentioned at TabPy Authentication page basic authentication is used at the moment (https://en.wikipedia.org/wiki/Basic_access_authentication) which means username (login) and password sent with each HTTP request to TabPy. This is why it is highly recommended to use a secured communication channel rather than plain text. For how to configure secure connection read Configuring HTTP vs HTTPS documentation page.

Tableau Desktop

For Tableau Desktop go to the main menu, Help, Settings and Performance, Manage External Service Connection. The screenshots below are for Tableau 2019.4.2:

Set connection type to be TabPy/External API, enter Server (host) and Port for your TabPy instance (localhost and 9004 on the screenshot below), set check mark for Sign with username and password and enter credentials for a user:

To confirm the credentials are valid click Test Connection button and popup message with confirming success (or failure details) will show:

Tableau Server

To configure Tableau Server connection to TabPy with authentication follow instructions at TSM Security page. At the moment this post is being written the latest available version of Tableau Server is 2019.4.2 and the steps will be setting up a connection and applying the changes:

c:\user\admin>tsm security vizql-extsvc-ssl enable --connection-type tabpy --extsvc-host my_tabpy_server --extsvc-port 9004 --extsvc-username alice --extsvc-password Secret_D0nt_Te11

c:\user\admin>tsm pending-changes apply

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TabPy: modifying default configuration

Where to look at?

It is very easy to install (with pip install tabpy command) TabPy and start (with tabpy command) TabPy instance… but what if you need to make changes is some configuration settings? You may want to use a different port because the default 9004 is in use by some other application, or you may need to run multiple TabPy instances on the same machine for some reason. Or you want to change the level of logging for it to be more/less verbose or location of the log file.

The first thing to look at is the documentation page for how to customize TabPy settings. As you can see there are some settings which names start with TABPY_ prefix – those can be overwritten with environment variables.

Modifying individual settings with environment variables

If you only need to modify one or two parameters the simplest way to do so is to set the value for the parameter by setting the environment variable with the same name. Example for Windows for how to modify default TabPy port:

(Python 3.6) C:\Users\oleks_000>set TABPY_PORT=6311

(Python 3.6) C:\Users\oleks_000>tabpy
2020-01-20,16:45:59 [DEBUG] (app.py:app:207): Parameter port set to "6311" from config file or environment variable
2020-01-20,16:45:59 [INFO] (app.py:app:93): Web service listening on port 6311

For macOS and Linux use export TABPY_PORT=6311 command instead of set command in the example above.

The environment variable set in the way shown above won’t keep its value between terminal sessions – as soon as the terminal is closed not just the value of the variable but the variable itself won’t exist anymore.

This is one reason to use a configuration file to preserve configuration settings. Another reason is in the file you can modify multiple settings at once and even have set of files for different configurations.

Starting TabPy with a configuration file

On TabPy documentation page mentioned above (https://github.com/tableau/TabPy/blob/master/docs/server-config.md#custom-settings) there is an example of a configuration file. Copy it to some local file and edit as needed.

In the file, you only need to specify settings that have to be different from defaults. Here’s the file I use for the next example:







format=%(asctime)s [%(levelname)s] (%(filename)s:%(module)s:%(lineno)d): %(message)s

I stored the file as c:\tabpy\demo.conf and now can use it when starting TabPy with specifying custom configuration using --config command-line parameter :

(Python 3.6) C:\Users\oleks_000>tabpy --config c:\TabPy\demo.conf
2020-01-20,17:02:12 [INFO] (app.py:app:280): Loading state from state file c:\users\oleks_000\appdata\local\conda\conda\envs\python 3.6\lib\site-packages\tabpy\tabpy_server\state.ini
2020-01-20,17:02:12 [INFO] (app.py:app:311): Password file is not specified: Authentication is not enabled
2020-01-20,17:02:12 [INFO] (app.py:app:327): Call context logging is disabled
2020-01-20,17:02:12 [INFO] (app.py:app:110): Initializing TabPy...
2020-01-20,17:02:12 [INFO] (callbacks.py:callbacks:42): Initializing TabPy Server...
2020-01-20,17:02:12 [INFO] (app.py:app:113): Done initializing TabPy.
2020-01-20,17:02:12 [INFO] (app.py:app:67): Setting max request size to 262144000 bytes
2020-01-20,17:02:12 [INFO] (callbacks.py:callbacks:62): Initializing models...
2020-01-20,17:02:12 [INFO] (app.py:app:93): Web service listening on port 6311

What are those logger settings I see in the configuration file?

Short answer – those are Python logger settings documentation for which you can find at Python logger documentation page. With those setting you can control what is logged (how verbose is the logging), where the log entries are stored (console, file, etc.), in what format (what is in the logged message), how to format timestamp for a message and so on.

This post explains some details about logger configuration for TabPy – How to Configure Logging in TabPy? Another post shows how to use colors for console logging – Add colors to TabPy console output.

And here is post explaining how to configure authentication for TabPy – How to configure TabPy with authentication and use it in Tableau.

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