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, and 3.10. As of the release of webcolors 1.12, 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.
Why aren’t rgb_to_rgb_percent() and rgb_percent_to_rgb() precise?¶
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
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 gray/grey. These colors are: darkgray/darkgrey, darkslategray/darkslategrey, dimgray/dimgrey, gray/grey, lightgray/lightgrey, lightslategray/lightslategrey, slategray/slategrey.
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
store its name-to-value mappings, simply
reversing those mappings risks inconsistency: swapping the keys and
values of a
dict 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 hsl() construct.
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 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
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.