GraphTerm: A notebook-like graphical terminal interface for

GraphTerm: A notebook-like graphical terminal interface for
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PROC. OF THE 12th PYTHON IN SCIENCE CONF. (SCIPY 2013)
GraphTerm: A notebook-like graphical terminal
interface for collaboration and inline data visualization
Ramalingam Saravanan∗†
http://www.youtube.com/watch?v=nO0ceHmTlDQ
F
Abstract—The notebook interface, which blends text and graphics, has been
in use for a number of years in commercial mathematical software and is now
finding more widespread usage in scientific Python with the availability browserbased front-ends like the Sage and IPython notebooks. This paper describes
a new open-source Python project, GraphTerm, that takes a slightly different
approach to blending text and graphics to create a notebook-like interface.
Rather than operating at the application level, it works at the unix shell level by
extending the command line interface to incorporate elements of the graphical
user interface. The XTerm terminal escape sequences are augmented to allow
any program to interactively display inline graphics (or other HTML content)
simply by writing to standard output.
GraphTerm is designed to be a drop-in replacement for the standard unix
terminal, with additional features for multiplexing sessions and easy deployment
in the cloud. The interface aims to be tablet-friendly, with features like clickable/tappable directory listings for navigating folders etc. The user can switch,
as needed, between standard line-at-a-time shell mode and the notebook mode,
where multiple lines of code are entered in cells, allowing for in-place editing
and re-execution. Multiple users can share terminal sessions for collaborative
computing.
GraphTerm is implemented in Python, using the Tornado web framework for
the server component and HTML+Javascript for the browser client. This paper
discusses the architecture and capabilities of GraphTerm, and provides usage
examples such as inline data visualization using matplotlib and the notebook
mode.
Index Terms—GUI, CLI, graphical user interface, command line interface,
notebook interface, graphical shell
Introduction
Text and graphics form important components of the user interface when working with computers. Early personal computers
only supported the textual user interface, more commonly
known as the command line interface (CLI). However, when
the Apple Macintosh popularized the graphical user interface
(GUI), it soon became the preferred means for interacting with
the computer. The GUI is more user-friendly, especially for
beginners, and provides a more pleasant visual experience.
The GUI typically provides buttons and widgets for the most
common tasks, whereas the CLI requires recalling and typing
out commands to accomplish tasks. However, the friendliness
of the GUI comes at a cost—it can be much more difficult to
* Corresponding author: sarava@tamu.edu
† Texas A&M University
c 2013 Ramalingam Saravanan. This is an open-access article
Copyright ○
distributed under the terms of the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium,
provided the original author and source are credited.
perform advanced tasks using the GUI as compared to using
the CLI. Using a GUI is analogous to using a phrase book
to express yourself in a foreign language, whereas using a
CLI is like learning words to form new phrases in the foreign
language. The former is more convenient for first-time and
casual users, whereas the latter provides the versatility required
by more advanced users.
The dichotomy between the textual and graphical modes
of interaction also extends to scientific data analysis tools.
Traditionally, commands for data analysis were typed into a
terminal window with an interactive shell and the graphical
output was displayed in a separate window. Some commercial
software, such as Mathematica and Maple, provided a more
integrated notebook interface that blended text and graphics,
thus combining aspects of the CLI with the GUI. One of the
exciting recent developments in scientific Python has been the
development of alternative, open source, notebook interfaces
for scientific computing and data analysis—the Sage and
IPython notebooks [Perez12]. Since Python is a more generalpurpose language than Mathematica or Maple, the notebook
interface could potentially reach a much wider audience.
A notebook display consists of a sequence of cells, each
of which can contain code, figures, or text (with markup).
Although originally developed for exploratory research, notebooks can be very useful for presentations and teaching as
well. They can provide step-by-step documentation of complex
tasks and can easily be shared. The cells in a notebook
do not necessarily have to be executed in the sequence in
which they appear. In this respect, the notebook interface
can be considered an expression of "literate programming",
where snippets of code are embedded in natural language
documentation that explains what the code does [Knuth84].
Another emerging area where the notebook interface
could serve as an important tool is reproducible research
[Stodden13]. As computational techniques are increasingly
being used in all areas of research, reproducing a research
finding requires not just the broad outline of the research
methodology but also documentation of the software development environment used for the study. The need for
reproducible research is highlighted by the recent controversy
surrounding the highly influential Reinhart-Rogoff study that
identified a negative relationship between a country’s debt
and its economic growth rate. A follow-up study [Herndon13]
identified a simple coding error that affects key findings of
GRAPHTERM: A NOTEBOOK-LIKE GRAPHICAL TERMINAL INTERFACE FOR COLLABORATION AND INLINE DATA VISUALIZATION
91
the original study. The self-documenting nature of code and
results presented in a notebook format can make it easy to
share and reproduce such computations.
Background
The author had some experience with commercial notebook
interfaces before, but used the IPython Notebook interface
for the first time in January 2013, when teaching an introductory undergraduate programming course for geoscientists
using Python. After initially using the command line Python
interpreter, the class switched to using IPython Notebook,
whose inline code editing and graphics display turned out
to be really convenient. The notebook interface was used
for presenting lecture material, and the students used it for
their programming assignments, turning in their notebooks for
grading (in PDF format) .
The author had previously been working on a project called
GraphTerm, which implements a "graphical terminal interface"
using a Python backend and a HTML5+Javascript frontend
[GraphTerm]. It was a follow-up to two earlier projects, the
browser-based AjaxTerm, and XMLTerm, a GUI-like browser
built using the Mozilla framework [Sarava00]. GraphTerm is
aimed at being a drop-in replacement for XTerm, the standard
unix terminal, with additional graphical and collaborative
features. It retains all the features of the CLI, including pipes,
wildcards, command recall, tab completion etc., and also
incorporates web-based sharing, as well as GUI-like features,
such as clickable folder navigation, draggable files, inline
image display etc. (There also other terminal projects with
similar goals, such as TermKit for OS X and Terminology for
Linux.)
The distinctive features of the notebook interface, such as
inline editing and graphics, are not specific to any particular
programming language or interactive shell. Also, the GraphTerm code already had the capability to incorporate GUI-like
features into the terminal. Therefore, it seemed worth experimenting with GraphTerm to see how far it could be extended to
support a generic, language-independent, notebook interface,
while still retaining full backward compatibility with the unix
terminal. The goal was to allow the terminal to be switched to
a notebook mode, regardless of what application was running
in the shell. The backward compatibility requirements and
the loose coupling between the notebook and the underlying
application could make it more fragile and restricted, but that
would be an unavoidable trade-off. The rest of this paper
reports on the results of this effort to combine the CLI, GUI,
and the notebook interface.
Implementation
The standard unix terminal supports two types of buffers:
(i) the normal scroll buffer that contains lines of text, and
(ii) the full screen buffer used by text editors like vi etc.
Special character strings known as escape sequences are output
by programs to switch the terminal between the two buffers
[XTerm]. GraphTerm currently supports most of the standard
XTerm escape sequences and introduces additional escape
sequences that allow display of HTML fragments in the scroll
Fig. 1: Architecture of GraphTerm. Browser client connects to
Tornado server using websockets. Hosts connect to server using TCP.
buffer and the full screen buffer. The HTML fragments can
contain just about anything that can be displayed on a web
page, including text with markup, tables, and images.
The GraphTerm server is written in pure python, using the
Tornado web framework, with websocket support. The browser
client uses standard HTML5+Javascript+CSS (with jQuery).
The code is released under the BSD License and the repository
is available on Github.
The GraphTerm server may be run on the desktop or on a
remote computer. Users create and access terminal sessions
by the connecting to the Graphterm server on the default
port 8900, either directly or through SSH port forwarding
(Figure 1). By default, the localhost on the computer where the
GraphTerm server is running is available for opening terminal
sessions. Other computers can also connect to the GraphTerm
server, on a different port (8899), to make them accessible as
hosts for connection from the browser.
A pseudo-tty (pty) device is opened on the host for each
terminal session. By setting the PROMPT_COMMAND environment variable, GraphTerm determines when the standard
output of the previous command ends, and the prompt for the
new command begins. The connection between the browser
and the GraphTerm server is implemented using websockets
(bi-directional HTTP). The GraphTerm server acts as a router
sending input from controlling browser terminal sessions to the
appropriate pty on the host computer, and transmitting output
from each pty to all connected browser terminal sessions.
All the scroll buffer and full screen buffer content is stored
on the server, which means that the terminal is persistent
across different browser sessions. For example, you can leave
the terminal on your desktop computer at work and access
the exact same content on your laptop browser when you
get home. This allows GraphTerm to be used like the GNU
screen or tmux programs. Storing the content on the server
also allows multiple users to share access to the same terminal
session for collaboration, similar to, e.g., Google Docs. This
means that multiple users will be able to view and modify a
GraphTerm notebook session in real time.
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Fig. 2: Output of helloworld.sh within GraphTerm, showing
inline HTML text and image.
PROC. OF THE 12th PYTHON IN SCIENCE CONF. (SCIPY 2013)
Fig. 3: Output of ls and gls commands for the same directory.
The names displayed by gls are hyperlinked, and may be clicked to
navigate to a folder or open a file.
The GraphTerm API
Programs running within a GraphTerm shell communicate
with it by writing to its standard output a block of text using
a format similar to a HTTP response, preceded and followed
by XTerm-like escape sequences:
\x1b[?1155;<cookie>h
{"content_type": "text/html", ...}
<div>
...
</div>
\x1b[?1155l
where <cookie> denotes a numeric value stored in the environment variable GTERM_COOKIE. This random cookie is a
security measure that prevents malicious files from accessing
GraphTerm. The opening escape sequence is followed by an
optional dictionary of header names and values, using JSON
format. This is followed by a blank line, and then any data
(such as the HTML fragment to be displayed).
A simple bash shell script, hello_world.sh, illustrates
this API:
#!/bin/bash
# A Hello World program using the GraphTerm API
prefix=https://raw.github.com/mitotic/graphterm
url=$prefix/master/graphterm/www/GTYY500.png
esc=‘printf "\033"‘
code="1155"
# Prefix escape sequence
echo "${esc}[?${code};${GTERM_COOKIE}h"
# Display text with HTML markup
echo ’<b>Hello</b>’
echo ’<b style="color: red;">World!</b><p>’
# Display inline image
echo "<a><img width="200" src=\"$url\"></a>"
# Suffix escape sequence
echo "${esc}[?${code}l"
If run within GraphTerm, the script produces the output shown
in Figure 2.
Features
GraphTerm is written in pure Python and the only dependency
is the tornado web server module. It can be installed
using easy_install or setuptools. Once the GraphTerm server program is started, it listens on port 8900 on
localhost by default, and any browser can be used to
connect to it and open new terminal sessions using the URL
http://localhost:8900. At this point, GraphTerm can
be used like a regular terminal, with commands like ls,
Fig. 4: Output of gls with icon display enabled. Clicking on
the folder icon for 00_vanderwalt (red rectangle) executes the
command cd 00_vanderwalt; gls -f via the command line
(green rectangle) to navigate to the folder and list its directory
contents. (This action also overwrites any immediate previous file
navigation command in the GraphTerm command history, to avoid
command clutter.)
vi, etc. However, to use the graphical capabilities of GraphTerm, one needs to use GraphTerm-aware versions of these
commands, with names like gls and gvi, that are part of
the command toolchain that is bundled with the code. The
toolchain commands communicate using pipes and may be
written any language, e.g., Bash shell script, Python etc., using
the API described above. The GUI-like features of GraphTerm
implemented using this toolchain are discussed and illustrated
below.
Clickable folders and files
The output of the standard ls command displays the directory
listing as plain text, whereas the gls command from the
toolchain displays a hyperlinked ("clickable") directory listing
(Figure 3).
By default, gls does not display icons or images in the
directory listing. However, icon display can be enabled using
the GraphTerm menubar (Figure 4).
You can navigate folders in GraphTerm using GUI-like
actions, like you would do in the Windows Explorer or the
Mac Finder, while retaining the ability to drop back to the CLI
GRAPHTERM: A NOTEBOOK-LIKE GRAPHICAL TERMINAL INTERFACE FOR COLLABORATION AND INLINE DATA VISUALIZATION
Fig. 5: File fig2.png is dragged from the Downloads folder from
the source terminal and dropped into the . (current directory) folder
icon displayed by gls in the destination terminal. This executes
the command mv /user/rsarava/Downloads/fig2.png .
in the destination terminal to move the file.
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Fig. 6: Two shared views of a GraphTerm terminal session showing
the output of the command head -20 episodeIV.txt on a
computer running OS X Lion. The left view is in a Firefox window
with the default theme and the right view shows the same terminal
in a Chrome window, using the stars3D perspective theme (which
currently does not work on Firefox).
Inline graphics
at any time. If the current command line is empty, clicking on
a hyperlinked folder will insert a new command line of the
form:
cd newdir; gls -f
which will change the current directory to newdir and list its
contents. Clicking on a hyperlinked filename will generate a
new command line to invoke platform-dependent commands
like open or xdg-open to open the file using the default
program for its file type. This feature illustrates one of the
basic design goals of GraphTerm, that each GUI-like action
should generate a corresponding shell command that actually
carries out that action. This allows the action to be logged and
reproduced later.
Drag and drop
GraphTerm currently provides limited support for drag-anddrop operations, including support for uploading/copying files
between terminal sessions on different computers connected
to the same GraphTerm server. As shown in Figure 5, when
a file is dragged from the source terminal and dropped into a
folder displayed in the destination terminal, a mv command is
generated to perform the task. Thus the GUI action is recorded
in the command line for future reference.
Session sharing and theming
GraphTerm terminal sessions can be shared between multiple
computers, with different types of access levels for additional
users accessing the same terminal, such as read-only access
or full read-write access. Since a GraphTerm terminal session
is just a web page, it also supports theming using CSS
stylesheets. The terminal sharing and theming are decoupled,
which means that two users can view the same terminal using
different themes (Figure 6)!
Since GraphTerm can display arbitrary HTML fragments, it is
easy to display graphical output from programs. The gimage
command in the toolchain can be used to display inline
images. The toolchain also includes the yweather command
to display the current weather forecast graphically using
the Yahoo Weather API. Other toolchain commands include
glandslide to use the Python-based landslide presentation
tool and greveal that uses reveal.js to display slideshows
within a GraphTerm window.
GraphTerm can be used for inline display of graphical
output from matplotlib (Figure 7). The API bundled
with GraphTerm uses the StringIO module to capture the
binary plot data using the png image output produced by the
Agg renderer and then displays the image using GraphTerm
escape sequences. A module called gmatplot is supplied
with GraphTerm to provide explicit access to this plotting
API. Another module gpylab is also provided, for monkey
patching existing plotting code to work within GraphTerm
with little or no changes. For example, if the Python interpreter
is invoked using the following command:
python -i $GTERM_DIR/bin/gpylab.py
then pylab functions like draw, figure, and show will
automatically use the Graphterm API to display inline graphics
(e.g. see the notebook example shown in Figure 8).
Since communication with GraphTerm occurs solely via
the standard output of a program, inline graphics can be
displayed from any plotting program, including commercial
software like IDL and other plotting packages like the NCAR
Command Language (NCL). Inline graphics display can also
be used across SSH login boundaries by including support for
the GraphTerm API in the plotting program on the remote
machine.
Notebook mode
GraphTerm can be switched from the normal terminal mode
to a blank notebook mode using the key sequence Shift-Enter
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PROC. OF THE 12th PYTHON IN SCIENCE CONF. (SCIPY 2013)
Fig. 7: Inline display of a 2-dimensional filled contour plot of surface
air temperature on the globe, generated by matplotlib. The code
for this plot is taken from the textbook by [Lin12].
Fig. 9: When switching back to the terminal mode after exiting the
notebook mode, the notebook contents can either be discarded or be
appended like normal terminal output, as shown above.
Fig. 8: GraphTerm notebook mode, where the notebook contents are
read from a file saved using the ipynb format. The first cell contains
Markdown text and the second cell contains python code to generate
a simple plot using matplotlib. Note the use of raw_input to
prompt the user for terminal input.
or using the menubar. The user can also click on a notebook
file displayed in the gls directory listing to open it and prefill the notebook cells with content from the file (Figure 8).
The notebook mode supports the normal terminal operations,
such as reading from the standard input (i.e., raw_input in
Python) and using debuggers, as well as GraphTerm extensions
like inline graphics. (Full screen terminal operations are not
supported in the notebook mode.)
Users can save the contents of the displayed notebook to
a file at any time. Users exit the notebook mode and revert
to the normal terminal mode using the menubar or simply by
typing Control-C. When exiting the notebook mode, users can
choose to either merge all the notebook content back into the
terminal session or discard it (Figure 9).
The notebook implementation in GraphTerm attempts to
preserve interoperability with the IPython Notebook to the
extent possible. GraphTerm can read and write notebooks
using the IPython Notebook format (*.ipynb), although
it uses the Markdown format for saving notebook content.
(Markdown was chosen as the native format because it is
more human-friendly than ReStructuredText or JSON, allows
easy concatenation or splitting of notebook files, and can
be processed by numerous Markdown-aware publishing and
presentation programs like landslide and reveal.js. )
GraphTerm supports many of the same keyboard shortcuts
as IPython Notebook. GraphTerm can also be used with
the command-line version of IPython. However, the generic,
loosely-coupled notebook interface supported by GraphTerm
will never be able to support all the features of IPython
Notebook.
Here is how the notebook mode is implemented within
GraphTerm: when the user switches to the notebook mode,
a separate scroll buffer is created for each cell. When the
user executes a line of code within a GraphTerm notebook
cell, the code output is parsed for prompts to decide whether
to continue to display the output in the output cell, or to
return focus to the input cell. This text-parsing approach does
make the GraphTerm notebook implementation somewhat
fragile, compared to other notebook implementations that have
a tighter coupling with the underlying code interpreter (or
kernel). However it allows GraphTerm to work with interactive
GRAPHTERM: A NOTEBOOK-LIKE GRAPHICAL TERMINAL INTERFACE FOR COLLABORATION AND INLINE DATA VISUALIZATION
95
collaborative computing and research.
R EFERENCES
[GraphTerm] GraphTerm home page http://code.mindmeldr.com/graphterm
[Herndon13] T. Herndon, M. Ash, and R. Pollin. Does High Public Debt
Consistently Stifle Economic Growth? A Critique of Reinhart
and Rogoff http://www.peri.umass.edu/fileadmin/pdf/working_
papers/working_papers_301-350/WP322.pdf
[Knuth84]
D. Knuth. Literate Programming. The Computer Journal
archive. Vol. 27 No. 2, May 1984, pp. 97-111 http://
literateprogramming.com/knuthweb.pdf
[Lin12]
J. Lin. A Hands-On Introduction to Using Python in the
Atmospheric and Oceanic Sciences [Chapter 9, Exercise 29,
p. 162] http://www.johnny-lin.com/pyintro
[Perez12]
F.
Perez.
The
IPython
notebook:
a
historical
retrospective.
Jan
2012
http://blog.fperez.org/2012/01/
ipython-notebook-historical.html
[Sarava00]
R. Saravanan. XMLterm: A Mozilla-based Semantic User Interface. XML.com, June 2000 http://www.xml.com/pub/a/2000/
06/07/xmlterm/
[Stodden13] V. Stodden, D. H. Bailey, J. Borwein, R. J. LeVeque, W.
Rider, and W. Stein. Setting the Default to Reproducible: Reproducibility in Computational and Experimental Mathematics.
February 2013 http://stodden.net/icerm_report.pdf
[XTerm]
XTerm Control Sequences http://invisible-island.net/xterm/
ctlseqs/ctlseqs.html
Fig. 10: Inline graphics in notebook mode when running the standard
R interpreter within GraphTerm.
shells for any platform, such as R (Figure 10) (or any interactive program with prompts, including closed source binaries
for languages like IDL).
Since all GraphTerm content is stored on the server, the
notebook can be accessed by multiple users simultaneously
for collaboration. Like inline graphics, the notebook mode
works transparently when executing interactive shells after a
remote SSH login, because all communication takes place via
the standard output of the shell. The non-graphical notebook
mode can be used without the remote program ever being
aware of the notebook interface. However, the remote program
will need to use the GraphTerm escape sequences to display
inline graphics within the notebook.
Conclusion
The GraphTerm project extends the standard unix terminal to
support many GUI-like capabilities, including inline graphics
display for data analysis and visualization. Adding features
like clickable folder navigation to the CLI also makes it
more touch-friendly, which is likely to be very useful on
tablet computers. Incorporating GUI actions within the CLI
allows recording of many user actions as scriptable commands,
facilitating reproducibility.
GraphTerm also demonstrates that the notebook interface
can be implemented as an extension of the CLI, by parsing
the textual output from interactive shells. This allows the
notebook interface to be "bolted on" to any interactive shell
program and to be used seamlessly even across SSH login
boundaries. The notebook features and the real-time session
sharing capabilities could make GraphTerm an useful tool for
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