SVG+Python based rendering of linguistics-style (constituent) trees
Project description
svgling
: syntax trees in python + svg
Author: Kyle Rawlins, kgr@jhu.edu
Dependencies: svgwrite
, python 3, (optional) cairosvg
Repository: https://github.com/rawlins/svgling/
Installation: download from github and use setuptools, or pip install svgling
for the current release version
License: MIT License
Overview
The svgling
package is a pure python package for doing single-pass rendering
of linguistics-style constituent trees into SVG. It is primarily intended for
integrating with Jupyter notebooks, but could be used to generate SVG diagrams
for all sorts of other purposes. It involves no javascript and so will work
in Jupyter without any plugins.
The basic interface is pretty simple: pass a tree-describing object to
svgling.draw_tree
(e.g. a tuple consisting of a label and a sequence of
daughter nodes, which may themselves be trees).
import svgling
svgling.draw_tree(("S", ("NP", ("D", "the"), ("N", "elephant")), ("VP", ("V", "saw"), ("NP", ("D", "the"), ("N", "rhinoceros")))))
This produces an SVG image like the following:
The tree drawing code accepts two main tree formats: lisp-style trees made from
lists of lists (or tuples of tuples), with node labels as strings, or trees from
the nltk
package, i.e. objects instantiating the
nltk.tree.Tree
API. The
following nltk code run in Jupyter, as long as svgling
has been installed,
produces an identical tree diagram to the above example:
nltk.Tree.fromstring("(S (NP (D the) (N elephant)) (VP (V saw) (NP (D the) (N rhinoceros))))")
On current versions of nltk
, the support goes both ways: the default (and
only) tree renderer in Jupyter is svgling
. If the package is installed, nltk
Trees will automatically render using svgling trees. For more control, you can
also provide a tree directly to the svgling.draw_tree
function, which allows
you to use options:
x = nltk.Tree.fromstring("(S (NP (D the) (N elephant)) (VP (V saw) (NP (D the) (N rhinoceros))))")
svgling.draw_tree(x, leaf_nodes_align=True)
Beyond basic tree-drawing, the package supports a number of flourishes like movement arrows. For documentation and examples, see the three .ipynb files in the root of this repository: (links below to nbviewer static rendered versions):
Core design principles and goals
- Be well suited for programmatic generation of tree diagrams (not just hand-customized diagrams).
- Be equally suited for theoretical linguistics and computational linguistics/NLP, at least for cases where the latter is targeting constituent trees. (This package is not aimed at dependency trees/graphs.)
- Do as much as possible with pure python (as opposed to python+javascript, or python+tk, or python+dot, or...).
Strengths and limitations
The svgling
package does its rendering in one pass -- it takes a tree
structure as input, produces an svg output, and that's it. Because of this, it
is extremely simple to use in Jupyter, and no messing with plugins or Jupyter
settings should be necessary. Because it is SVG-based, scaling and embedding in
any web context should work smoothly. It also has minimal dependencies, just
one package that provides an abstraction layer over generating svg. (If you're
interested in programmatic diagramming in svg for Jupyter, I do recommend
svgwrite
, it's under active maintenance
and has a very pleasant API + good documentation.)
Single-pass rendering also places limitations on what can be done. One of the
challenges is that it mostly uses absolute position, and the exact position and
width of text elements can't be determined without actually rendering to some
device and seeing what happens. In addition, the exact details of rendering are
in various ways at the mercy of the rendering device. This all means that
svgling
uses a bunch of tricks to estimate node size and width, and won't
always be perfect on all devices. This situation also places some hard
limitations on how far svgling
can be extended without adding javascript or
other multi-pass rendering techniques. For example, I would eventually like to
allow mathjax in nodes, and allow nodes with complex / multi-line shapes, but at
the moment this does not seem possible in pure SVG without javascript on the
client side. The package does provide basic support for hybrid HTML/SVG tree
diagrams that allow complex nodes, including MathJax, but with substantial
limitations.
There are many things that it might be nice to add to this package; if you find
svgling
useful, have any requests, or find any bugs, please let me know.
Compatibility
The SVG files produced by svgling
should be compatible with all major browsers
(Chrome, Firefox, Safari, Edge) on both desktop and mobile; if you find a
compatibility issue with some browser, please report it as a
bug. It also supports all major
interactive editing packages that I am aware of.
There are various ways to convert the generated SVG files to other formats,
including raster ones, but the recommended/supported way to do this
programmatically is via the cairosvg
package.
svgling.utils
provides some convenience functions for conversion to
PNG/PDF/PS using cairosvg. See the "Compatibility and Conversion" section of
the svgling manual for more details. Note that cairosvg
is an optional
dependency of svgling
, so won't necessarily be installed by default.
Project details
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