Startup hacks and engineering miracles from your exhausted friends at Faraday

How to finally use headless Chrome to power your automated tests

Derek Kastner on

Google Chrome version 59 will ship with the headless
. This means you can test your web applications using chrome without needing xvfb. One problem: the latest chromedriver (version 2.29) doesn't support versions of Chrome higher than 58.

The solution is to build the latest chromedriver that supports the latest chrome/chromium. Google does not make nightly builds of chromedriver public, you have to download the chromium source and build
chromedriver yourself.

How all the pieces work together

Cucumber uses the capybara gem to send commands to selenium-webdriver. Selenium-webdriver in turn starts up your local copy of chromedriver, which then starts up chrome and controls the browser through a special debug port.

To get the latest chromium, I used a tool on GitHub that downloads the latest snapshot compiled for Linux.

To get the latest chromedriver, I followed the
build instructions.

Configuring the tests

When configuring capybara, you need to tell selenium-webdriver the path to your custom chromium binary and send the --headless flag, along with other flags
you'll likely need in a CI build node environment.

For running in docker:

Capybara.register_driver :headless_chromium do |app|  
  caps =                       
    "chromeOptions" => {                                                         
      'binary' => "/chromium-latest-linux/466395/chrome-linux/chrome",           
      'args' => %w{headless no-sandbox disable-gpu}                              
  driver =                                       
    browser: :chrome,                                                            
    desired_capabilities: caps                                                   

Capybara.default_driver = :headless_chromium  

Now, capybara will drive a headless chromium!

Two magic words for greater independence and communication

Thomas Bryenton on

What if there were two words you could add to any email to get your team to weigh in quickly?

There are: DEFAULT DO

How default-do works

  1. Write up a final version of what you'll be doing (your "default do")
  2. Tell teammates you're about to do this thing
  3. Do the thing

Just default do it

I use default-do every day to keep Faraday moving:

  • Emails
  • Code
  • Mockups
  • Decisions
  • Policies
  • Blog posts!

It doesn't matter what it is: if I'm confident it's the right thing to do, I'll tell my team I'm about to do it, pause, then just do it.

Don't wear it out. If you don't really want feedback, don't ask, and if you need it, your default isn't "do," it's "don't."

Use headless chromium with capybara and selenium webdriver - today!

Seamus Abshere on

UPDATE: we have a new version of this post out that resolves some of the gotchas below.

Here's a Rubyist's magic incantation to run headless chromium with selenium-webdriver and capybara: (it will be similar in other languages)

require 'selenium-webdriver'

Capybara.register_driver :headless_chromium do |app|  
  caps =
    "chromeOptions" => {
      'binary' => '/home/myuser/chrome-linux-440004/chrome',
      'args' => ['headless', 'disable-gpu']
  driver =
    browser: :chrome,
    desired_capabilities: caps


  1. You need a chromium (chrome) binary that reports version 57 (version 59 is too new). For example, snapshot 440004 - just download and unzip.
  2. You need a recent chromedriver binary with support for headless chrome. For example, snapshot 460342 - just download and unzip.
  3. If you get the error unrecognized chrome version, then see (1) above - you probably have a too-recent chromium.

Thanks to @dkastner!

Antipattern: Using Ruby's Hash#[]

Seamus Abshere on

This is part of our antipatterns series. Ouch! Updated for 2017!

Ask yourself why you're using Hash#[]. It is is a great way to introduce silent bugs into your app.

Use Hash#fetch if you expect the value to exist

That way you get sensible error messages.

#> params = {}

#> params.fetch('really').fetch('important')
KeyError: key not found: "really"  

Use Hash#dig if you don't care

Because you don't get idiotic, non-semantic NoMethodError: undefined method '[]' for nil:NilClass errors.

#> params.dig('really', 'important')
=> nil

Avoid Hash#[] because... just... why?

#> params['really']['important']
NoMethodError: undefined method `[]' for nil:NilClass  

Special case: ENV

The Twelve-Factor App has us all using environment variables. But most of us default to ENV#[] to look stuff up... even if it's critical. Bad idea! Use fetch!

#> ENV['REALLY_IMPORTANT'] == 'thing'
=> false # well i hope you didn't need that

#> ENV.fetch('REALLY_IMPORTANT') == 'thing'
KeyError: key not found: "REALLY_IMPORTANT"  

Plancha: how to flatten multi-sheet excel workbooks

Bill Morris on

This is part of our series on data science because it belongs in your toolchain.

If you work with data long enough - actually scratch that; if you work with data for more than a week - you'll run into the dreaded multi sheet (or tab) excel workbook. Sometimes the sheets are unrelated, but other times they should really all be stacked together in the same table, ideally in a more-interoperable format than .xlsx:


Enter plancha. Named for the trusty tortilla press, we built this simple CLI tool to flatten multi-sheet excel files, resolve header mismatches, and return a pipeline-friendly csv, like this:



This is a node.js tool, so use npm:

npm install plancha -g


Just feed it an input .xlsx file:

plancha -i myfile.xlsx

Happy data-pressing!

scrubcsv: now with null value removal

Seamus Abshere on

This is part of our series on data science because it belongs in your toolchain. Happy Null Removal!

The latest version of scrubcsv has built-in null value removal:

$ cat a.csv

$ scrubcsv -n 'null|n/a' a.csv

See how null and n/a went away?

Get the latest version with

$ cargo install scrubcsv -f

How to export a Dataiku DSS (or any scikit-learn) model to PMML

Andy Rossmeissl on

This post is part of our data science series

At Faraday we use Dataiku to do ad hoc exploratory data science work, and especially for investigating new predictive techniques before building them into our platform.

Dataiku is awesome and has an incredibly responsive team. One drawback for me, however, has been Dataiku's lack of support for PMML, a standard serialization format for predictive models and their associated apparatus.

Luckily with a little hacking you can export a Dataiku model to PMML. And this technique can work anywhere you have a scikit-learn-based model you're trying to export.


We're going to use Dataiku's built-in Python environment, which lives in your DSS data directory (generally /Users/username/Library/DataScienceStudio/dss_home on a Mac). We need to add a couple libraries first:

$ ./bin/pip install sklearn_pandas
$ ./bin/pip install git+

You'll also need a working JDK. If this doesn't work:

$ java -version
java version "1.8.0_121"  

Then install a JDK. (On Mac: brew cask install java.)

Locate your classifier

OK, now let's get our hands on the model you're trying to export. Maybe it's already in memory, but more likely it's pickled on disk. With Dataiku, you'll find your pickled classifier in a path that looks like this:


There it is, clf.pkl. It's helpful to copy this file into your working dir so we don't accidentally disturb it.

Export the model to PMML

Now let's start up an interactive Python console — again using Dataiku's built-in environment:

$ ./bin/python
Python 2.7.10 (default, Oct 23 2015, 19:19:21)  

First let's load up some libraries:

>>> from sklearn.externals import joblib
>>> from sklearn2pmml import PMMLPipeline
>>> from sklearn2pmml import sklearn2pmml

Now we'll unmarshal the model using joblib, a pickle-compatible serialization library:

>>> clf = joblib.load('/path/to/clf.pkl')

Here's the only tricky part: we have to wrap the trained estimator in a Pipeline-like object that sklearn2pmml understands. (This is likely to get less tricky soon.)

>>> pipeline = PMMLPipeline([
...   ("estimator", clf)
... ])

And finally perform the export:

>>> sklearn2pmml(pipeline, "clf.pmml")
INFO: Parsing PKL..  
INFO: Marshalled PMML in 714 ms.  

All done! The heavy lifting here is done by sklearn2pmml, which wraps the JPMML-SkLearn library. Thanks to Villu Ruusmann in particular for his help.

How we made our CSV processing 142x faster

Bill Morris on

This post is part of our data science hacks series

At Faraday, we've long used csvkit to understand, transform, and beat senseless our many streams of data. However, even this inimitable swiss army knife can be improved on - we've switched to xsv.

xsv is a fast CSV-parsing toolkit written in Rust that mostly matches the functionality of csvkit (including the clutch ability to pipe between modules), with a few extras tacked on (like smart sampling). Did I mention it's fast? In a standup comparison, I ran the "stats" module of XSV against "csvstat" from csvkit, on a 30k-line, 400-column CSV file:

  • Python-based csvkit chews through it in a respectable-and-now-expected 4m16s.

  • xsv takes 1.8 seconds. I don't even have time for a sip of my coffee.

The difference between csvkit and xsv is partly defined by scale; both tools are plenty fast on smaller datasets. But once you get into 10MB-and-upward range, xsv's processing speed pulls away exponentially.

If you've been using csvkit forever (like me), or if you want to be able to transform and analyze CSVs without loading them into a DB, give xsv a shot:

Install Rust

curl -sSf | sh  

. . . which also gives you the rust package manager cargo, which lets you:

Install xsv

cargo install xsv  

Then be sure your PATH is configured correctly:

export PATH=~/.cargo/bin:$PATH  

. . . and try it out on a demo CSV with 10k rows, some messy strings, and multiple data types:

curl \  
| xsv stats \
| xsv table

(xsv table formats the data so it's readable in the console):

field           type     sum                 min                  max                  min_length  max_length  mean                stddev  
id              Integer  5005000             1                    1000                 1           4           500.49999999999994  288.6749902572106  
first_name      Unicode                      Aaron                Willie               3           11  
last_name       Unicode                      Adams                Young                3           10  
email           Unicode              12          34  
gender          Unicode                      Female               Male                 4           6  
ip_address      Unicode                     9           15  
value           Unicode                      $1007.98             $999.37              0           8  
company         Unicode                      Abata                Zoovu                0           13  
lat             Float    243963.82509999987  -47.75034            69.70287             0           9           24.42080331331331   24.98767816017553  
lon             Float    443214.19009999954  -179.12198           170.29993            0           10          44.36578479479489   71.16647723898215  
messed_up_data  Unicode                      !@#$%^&*()           𠜎𠜱𠝹𠱓𠱸𠲖𠳏       0           393  
version         Unicode                      0.1.1                9.99                 3           14  

Happy parsing!

scrubcsv: clean CSVs, drop bad lines

Seamus Abshere on

This is part of our series on things that are obvious once you see them - and our data science series because it belongs in your toolchain.

Lies, damn lies, and commercial CSV export modules. Who wrote these things? On what planet would this be acceptable? Whatever.

Name,What's wrong  
"Robert "Bob" Smith",quotes inside quotes
Robert "Bob" Smith,quotes in the middle  
Robert Bob" Smith,unmatched quote  

Ruby dies immediately trying to read it:

$ irb
irb(main):001:0> require 'csv'  
=> true
CSV::MalformedCSVError: Missing or stray quote in line 2  

Introducing scrubcsv, a is a lightning-fast static binary written in Rust that best-effort parses CSV and then immediately dumps back out 100% guaranteed standards-compliant CSV. Top speed? About 67mb/s.

$ scrubcsv broken.csv > fixed.csv
4 rows (0 bad) in 0.00 seconds, 787.13 KiB/sec

$ cat fixed.csv
Name,What's wrong  
"Robert Bob"" Smith""",quotes inside quotes
"Robert ""Bob"" Smith",quotes in the middle
"Robert Bob"" Smith",unmatched quote

It uses BurntSushi's world-beating CSV parser which is almost certainly faster than your SSD.

No MD5, SHA1, or SHA256 collisions for US addresses

Seamus Abshere on

I calculated hashes of single-family home addresses in the United States:

create table hashtest as (  
    digest(upper(house_number_and_street || ',' || city || ',' || state), 'md5') as "md5",
    digest(upper(house_number_and_street || ',' || city || ',' || state), 'sha1') as "sha1",
    digest(upper(house_number_and_street || ',' || city || ',' || state), 'sha256') as "sha256"
  from households


=> select upper(house_number_and_street || ',' || city || ',' || state) "key", digest(upper(house_number_and_street || ',' || city || ',' || state), 'md5') "md5" from households limit 1;
             key               |                md5
 1024 PENINSULA DR,WESTWOOD,CA | \x511cdfb25d6b77d45742ed0407b5c2ef
(1 row)

Then I counted the distinct hashes:

=> select count(distinct md5) md5, count(distinct sha1) sha1, count(distinct sha256) sha256, count(*) from hashtest;
   md5    |   sha1   |  sha256  |  count
 78224992 | 78224992 | 78224992 | 81087108
(1 row)

Some of the addresses are repeated in the database because the APNs are identical, but the conclusion is that we have 78 million uniques and no hash collisions with the algorithms tested.