Author: Kyle Rawlins, kgr@jhu.edu
Dependencies: svgwrite
, Python 2.7
Repository: https://github.com/rawlins/svgling/
Installation: download and use setuptools, or pip install svgling
License: MIT License
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, as long as svgling
has been imported, produces an
identical tree diagram to the above example, though by a very different route:
import svgling
nltk.Tree.fromstring("(S (NP (D the) (N elephant)) (VP (V saw) (NP (D the) (N rhinoceros))))")
(That is, svgling
monkey-patches NLTK to use SVG-based tree drawing code. You
may also want to call svgling.disable_nltk_png()
to fully disable the
default NLTK png renderer, especially if you're on a mac or windows 64, or are
running NLTK on a headless device; see nltk issue
#1887 for use-cases).)
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):
- 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...).
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 development
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.