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Write SVG files with Python.

Project description

svg_ultralight

The most straightforward way to create SVG files with Python.

Four principal functions:

from svg_ultralight import new_svg_root, write_svg, write_png_from_svg, write_png

One convenience:

from svg_ultralight import NSMAP

new_svg_root

x_: Optional[float],
y_: Optional[float],
width_: Optional[float],
height_: Optional[float],
pad_: float = 0
dpu_: float = 1
nsmap: Optional[Dict[str, str]] = None (svg_ultralight.NSMAP if None)
**attributes: Union[float, str],
-> etree.Element

Create an svg root element from viewBox style arguments and provide the necessary svg-specific attributes and namespaces. This is your window onto the scene.

Three ways to call:

  1. The trailing-underscore arguments are the same you'd use to create a rect element (plus pad_ and dpu_). new_svg_root will infer viewBox, width, and height svg attributes from these values.
  2. Use the svg attributes you already know: viewBox, width, height, etc. These will be written to the xml file.
  3. Of course, you can combine 1. and 2. if you know what you're doing.

See namespaces below.

  • x_: x value in upper-left corner
  • y_: y value in upper-left corner
  • width_: width of viewBox
  • height_: height of viewBox
  • pad_: the one small convenience I've provided. Optionally increase viewBox by pad in all directions.
  • dpu_: pixels per viewBox unit for output png images.
  • nsmap: namespaces. (defaults to svg_ultralight.NSMAP). Available as an argument should you wish to add additional namespaces. To do this, add items to NSMAP then call with nsmap=NSMAP.
  • **attributes: the trailing-underscore arguments are an optional shortcut for creating a scene. The entire svg interface is available to you through kwargs. See A few helpers below for details on attribute-name translation between Python and xml (the short version: this_name becomes this-name and this_ becomes this)

namespaces (svg_ultralight.NSMAP)

new_svg_root will create a root with several available namespaces.

  • "dc": "http://purl.org/dc/elements/1.1/"
  • "cc": "http://creativecommons.org/ns#"
  • "rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  • "svg": "http://www.w3.org/2000/svg"
  • "xlink": "http://www.w3.org/1999/xlink"
  • "sodipodi": "http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
  • "inkscape": "http://www.inkscape.org/namespaces/inkscape"

I have made these available to you as svg_ultralight.NSMAP

write_svg

svg: str,
xml: etree.Element,
stylesheet: Optional[str] = None,
do_link_css: bool = False,
**tostring_kwargs,
-> str:

Write an xml element as an svg file. This will link or inline your css code and insert the necessary declaration, doctype, and processing instructions.

  • svg: path to output file (include extension .svg)
  • param xml: root node of your svg geometry (created by new_svg_root)
  • stylesheet: optional path to a css stylesheet
  • do_link_css: link to stylesheet, else (default) write contents of stylesheet into svg (ignored if stylesheet is None). If you have a stylesheet somewhere, the default action is to dump the entire contents into your svg file. Linking to the stylesheet is more elegant, but inlining always works.
  • **tostring_kwargs: optional kwarg arguments for lxml.etree.tostring. Passing xml_declaration=True by itself will create an xml declaration with encoding set to UTF-8 and an svg DOCTYPE. These defaults can be overridden with keyword arguments encoding and doctype. If you don't know what this is, you can probably get away without it.
  • returns: for convenience, returns svg filename (svg)
  • effects: creates svg file at svg

write_png_from_svg

inkscape_exe: str,
svg: str
png: Optional[str]
-> str

Convert an svg file to a png. Python does not have a library for this. That has an upside, as any library would be one more set of svg implementation idiosyncrasies we'd have to deal with. Inkscape will convert the file. This function provides the necessary command-line arguments.

  • inkscape_exe: path to inkscape.exe
  • svg: path to svg file
  • png: optional path to png output (if not given, png name will be inferred from svg: 'name.svg' becomes 'name.png')
  • return: png filename
  • effects: creates png file at png (or infers png path and filename from svg)

write_png

inkscape_exe: str,
png: str,
xml: etree.Element,
stylesheet: Optional[str] = None
-> str

Create a png without writing an initial svg to your filesystem. This is not faster (it may be slightly slower), but it may be important when writing many images (animation frames) to your filesystem.

  • inkscape_exe: path to inkscape.exe
  • png: path to output file (include extension .png)
  • param xml: root node of your svg geometry (created by new_svg_root)
  • stylesheet: optional path to a css stylesheet
  • returns: for convenience, returns png filename (png)
  • effects: creates png file at png

A few helpers:

from svg_ultralight.constructors import new_element, new_sub_element

I do want to keep this ultralight and avoid creating some pseudo scripting language between Python and lxml, but here are two very simple, very optional functions to save your having to str() every argument to etree.Element.

constructors.new_element

tag: str
**params: Union[str, float]
-> etree.Element

Python allows underscores in variable names; xml uses dashes.

Python understands numbers; xml wants strings.

This is a convenience function to swap "_" for "-" and 10.2 for "10.2" before creating an xml element.

Translates numbers to strings

>>> elem = new_element('line', x1=0, y1=0, x2=5, y2=5)
>>> etree.tostring(elem)
b'<line x1="0" y1="0" x2="5" y2="5"/>'

Translates underscores to hyphens

>>> elem = new_element('line', stroke_width=1)
>>> etree.tostring(elem)
b'<line stroke-width="1"/>'

Removes trailing underscores. You'll almost certainly want to use reserved names like class as svg parameters. This can be done by passing the name with a trailing underscore.

>>> elem = new_element('line', class_='thick_line')
>>> etree.tostring(elem)
b'<line class="thick_line"/>'

Special handling for a 'text' argument. Places value between element tags.

>>> elem = new_element('text', text='please star my project')
>>> etree.tostring(elem)
b'<text>please star my project</text>'

constructors.new_sub_element

parent: etree.Element
tag: str
**params: Union[str, float]
-> etree.Element

As above, but creates a subelement.

>>> parent = etree.Element('g')
>>> _ = new_sub_element('rect')
>>> etree.tostring(parent)
b'<g><rect/></g>'

update_element and deepcopy_element

These are two more ways to add params with the above-described name and type conversion. Again unnecessary, but potentially helpful. Easily understood from the code or docstrings.

Extras:

query.map_ids_to_bounding_boxes

Python cannot parse an svg file. Python can create an svg file, and Inkscape can parse (and inspect) it. Inkscape has a command-line interface capable of reading an svg file and returning some limited information. This is the only way I know for a Python program to:

  1. create an svg file (optionally without writing to filesystem)
  2. query the svg file for bounding-box information
  3. create an adjusted svg file.

This would be necessary for, e.g., algorithmically fitting text in a box.

from svg_ultralight.queries import map_ids_to_bounding_boxes

You can get a tiny bit more sophisticated with Inkscape bounding-box queries, but not much. This will give you pretty much all you can get out of it.

query.get_bounding_box

Get the bounding box around an svg element. Works with group elements.

Internally, this just creates an svg file around your element then calls map_ids_to_bounding_boxes.

from svg_ultralight.queries import get_bounding_box

animate.write_gif

Create an animated gif from a sequence of png filenames. This is a Pillow one-liner, but it's convenient for me to have it, so it might be convenient for you.

from svg_ultralight.animate import write_gif

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