## 1. Introduction¶

Version control repositories like CVS, Subversion or Git can be a real gold mine for software developers. They contain every change to the source code including the date (the "when"), the responsible developer (the "who"), as well as little message that describes the intention (the "what") of a change.

In this notebook, we will analyze the evolution of a very famous open-source project – the Linux kernel. The Linux kernel is the heart of some Linux distributions like Debian, Ubuntu or CentOS.

We get some first insights into the work of the development efforts by

• identifying the TOP 10 contributors and
• visualizing the commits over the years.

Linus Torvalds, the (spoiler alert!) main contributor to the Linux kernel (and also the creator of Git), created a mirror of the Linux repository on GitHub. It contains the complete history of kernel development for the last 13 years.

For our analysis, we will use a Git log file with the following content:

In [176]:
# Printing the content of git_log_excerpt.csv
log = open('datasets/git_log_excerpt.csv', 'r')

1502382966#Linus Torvalds
1501368308#Max Gurtovoy
1501625560#James Smart
1501625559#James Smart
1500568442#Martin Wilck
1502273719#Xin Long
1502278684#Nikolay Borisov
1502238384#Girish Moodalbail
1502228709#Florian Fainelli
1502223836#Jon Paul Maloy


## 2. Reading in the dataset¶

The dataset was created by using the command git log --encoding=latin-1 --pretty="%at#%aN". The latin-1 encoded text output was saved in a header-less csv file. In this file, each row is a commit entry with the following information:

• timestamp: the time of the commit as a UNIX timestamp in seconds since 1970-01-01 00:00:00 (Git log placeholder "%at")
• author: the name of the author that performed the commit (Git log placeholder "%aN")

The columns are separated by the number sign #. The complete dataset is in the datasets/ directory. It is a gz-compressed csv file named git_log.gz.

In [178]:
# Loading in the pandas module
import pandas as pd

# Reading in the log file

# Printing out the first 5 rows

    timestamp          author
0  1502826583  Linus Torvalds
3  1501882480       Kees Cook
4  1497271395       Rob Clark


## 3. Getting an overview¶

The dataset contains the information about every single code contribution (a "commit") to the Linux kernel over the last 13 years. We'll first take a look at the number of authors and their commits to the repository.

In [180]:
# calculating number of commits
number_of_commits = git_log.shape[0]

# calculating number of authors
number_of_authors = len(git_log.dropna().author.unique())

# printing out the results
print("%s authors committed %s code changes." % (number_of_authors, number_of_commits))

17385 authors committed 699071 code changes.


## 4. Finding the TOP 10 contributors¶

There are some very important people that changed the Linux kernel very often. To see if there are any bottlenecks, we take a look at the TOP 10 authors with the most commits.

In [182]:
# Identifying the top 10 authors
top_10_authors = git_log.groupby(['author']).agg('count').sort_values(by=['timestamp'], ascending=False)[0:10]

# Listing contents of 'top_10_authors'
top_10_authors

Out[182]:
timestamp
author
Linus Torvalds 23361
David S. Miller 9106
Mark Brown 6802
Takashi Iwai 6209
Al Viro 6006
H Hartley Sweeten 5938
Ingo Molnar 5344
Mauro Carvalho Chehab 5204
Arnd Bergmann 4890
Greg Kroah-Hartman 4580

## 5. Wrangling the data¶

For our analysis, we want to visualize the contributions over time. For this, we use the information in the timestamp column to create a time series-based column.

In [184]:
# converting the timestamp column
git_log.timestamp = pd.to_datetime(git_log['timestamp'], unit='s')

# summarizing the converted timestamp column
git_log.timestamp.describe()

Out[184]:
count                  699071
unique                 668448
top       2008-09-04 05:30:19
freq                       99
first     1970-01-01 00:00:01
last      2037-04-25 08:08:26
Name: timestamp, dtype: object

## 6. Treating wrong timestamps¶

As we can see from the results above, some contributors had their operating system's time incorrectly set when they committed to the repository. We'll clean up the timestamp column by dropping the rows with the incorrect timestamps.

In [186]:
# determining the first real commit timestamp
from_2005_to_2018 = (git_log.timestamp > '2005-04-16 22:20:00') & (git_log.timestamp <= '2018-02-17 00:00:00')
valid_timestamps = git_log[from_2005_to_2018].sort_values(by=['timestamp']).timestamp

valid_timestamps = valid_timestamps.reset_index()

first_commit_timestamp = valid_timestamps.timestamp[0]

# determining the last sensible commit timestamp
last_commit_timestamp = valid_timestamps.timestamp[len(valid_timestamps)-1]

# filtering out wrong timestamps
corrected_log = git_log[(git_log.timestamp >= first_commit_timestamp) & (git_log.timestamp <= last_commit_timestamp)]

# summarizing the corrected timestamp column
corrected_log.describe()

Out[186]:
timestamp author
count 698569 698568
unique 667977 17375
top 2008-09-04 05:30:19 Linus Torvalds
freq 99 23361
first 2005-04-16 22:20:36 NaN
last 2017-10-03 12:57:00 NaN

## 7. Grouping commits per year¶

To find out how the development activity has increased over time, we'll group the commits by year and count them up.

In [188]:
# Counting the no. commits per year
# commits_per_year = corrected_log.groupby(corrected_log.timestamp.dt.year).agg('count')
commits_per_year = corrected_log.groupby(pd.Grouper(key='timestamp', freq='AS')).agg('count')

# Listing the first rows

            author
timestamp
2005-01-01   16229
2006-01-01   29255
2007-01-01   33759
2008-01-01   48847
2009-01-01   52572


## 8. Visualizing the history of Linux¶

Finally, we'll make a plot out of these counts to better see how the development effort on Linux has increased over the the last few years.

In [190]:
# Setting up plotting in Jupyter notebooks
%matplotlib inline

# plot the data
commits_per_year.plot(title='Linux commits evolution', kind='bar', legend='off')

Out[190]:
<matplotlib.axes._subplots.AxesSubplot at 0x7f7b157f0b38>

## 9. Conclusion¶

Thanks to the solid foundation and caretaking of Linux Torvalds, many other developers are now able to contribute to the Linux kernel as well. There is no decrease of development activity at sight!

In [192]:
# calculating or setting the year with the most commits to Linux

year_with_most_commits = commits_per_year.idxmax()