Frequently asked questions#
The following notes answer common questions, and may be useful to you when using webcolors.
What versions of Python are supported?#
The webcolors module supports and is tested on Python 3.7, 3.8, 3.9, 3.10, and 3.11. As of the release of webcolors 1.13, these are the only versions of Python receiving upstream security support from the Python core team.
How closely does this module follow the standards?#
As closely as is practical (see below regarding floating-point values), within the supported formats; the webcolors module was written with the relevant standards documents close at hand. See the conformance documentation for details.
This is due to limitations in the representation of floating-point numbers in
programming languages. Python, like many programming languages, uses IEEE
floating-point, which is inherently
imprecise for some values. This imprecision only appears when converting
between integer and percentage
`rgb()` triplets, as in
To work around this, some common values (255, 128, 64, 32, 16 and 0) are
handled as special cases, with hard-coded precise results. For all other
values, conversion to percentage
rgb() triplet uses a standard Python
float, rounding the result to two decimal places.
See the conformance documentation for details on how this affects testing.
Why does webcolors prefer American spellings?#
In CSS3, several color names are defined multiple times with identical values,
to support both American and British spelling variants for
"grey". These colors are:
Using any of the conversions from names to other formats
name_to_rgb_percent()) will accept either spelling provided
the spec argument is
However, converting from other formats to a name requires picking one of these
spellings. Since webcolors uses a Python
dict to store its
name-to-value mappings, simply reversing those
mappings risks inconsistency: swapping the keys and values of a
in Python depends on the key order, which varies from one version of Python to
another and in several supported Python versions is not guaranteed to be
consistent and/or is documented as an implementation detail not to be relied
on. So webcolors must manually pick a spelling to normalize to, and chooses
gray. This choice was made for consistency with HTML 4, CSS1, and CSS2, each
of which only allowed gray.
Why aren’t HSL values supported?#
In the author’s experience, actual use of HSL values on the web is extremely
rare; the overwhelming majority of all colors used on the web are specified
using sRGB, through hexadecimal color values or through integer or percentage
rgb() triplets. This decreases the importance of supporting the
Additionally, Python already has the
colorsys module in the standard
library, which offers functions for converting between RGB, HSL, HSV and YIQ
color systems. If you need conversion to/from HSL or another color system, use
Why aren’t alpha-channel constructs like
Because the alpha-channel information can’t really be usefully converted. As of
hsla() construct is the only other color format that carries
alpha-channel information, and as explained above, HSL colors are not supported
in this module.
The in-progress W3C CSS Colors Level 4 module does provide an 8-digit
hexadecimal color representation where the final two digits carry alpha-channel
information. If and when that module becomes a W3C Recommendation with broad
support in web client software, support for alpha-channel constructs in this
module may be re-evaluated, though it would still be limited to converting
between only those constructs which carry alpha-channel information (for
rgba() or an eight-digit hexadecimal color value could not be
losslessly round-tripped to a color name and back).
Why not use a more object-oriented design with classes for the colors?#
Representing color values with Python classes would introduce overhead for no real gain. Real-world use cases tend to involve working directly with the actual values, so settling on conventions for how to represent them as Python types, and then offering a function-based interface, accomplishes everything needed without the additional indirection layer of having to instantiate and serialize a color-wrapping object.
Keeping a function-based interface also maintains consistency with Python’s
colorsys module which has the same style of interface for
converting amongst color spaces.
Note that if an object-oriented interface is desired, the third-party colormath module does have a class-based interface (and rightly so, as it offers a wider range of color representation and manipulation options than webcolors).
How am I allowed to use this module?#
The webcolors module is distributed under a three-clause BSD license. This is an open-source license
which grants you broad freedom to use, redistribute, modify and distribute
modified versions of webcolors. For details, see the file
LICENSE in the
source distribution of webcolors.
I found a bug or want to make an improvement!#
The canonical development repository for webcolors is online at <https://github.com/ubernostrum/webcolors>. Issues and pull requests can both be filed there.