Frequently asked questions

The following notes answer common questions, and may be useful to you when using webcolors.

What versions of Python are supported?

On Python 2, webcolors supports and is tested on Python 2.7. On Python 3, webcolors supports and is tested on Python 3.3, 3.4 and 3.5. It is expected that webcolors 1.7 will also work without modification on Python 3.6 once it is released.

These Python version requirements are due to a combination of factors:

  • On Python 2, only 2.7 still receives official security support from Python’s development team. Although some third parties continue to provide unofficial security support for earlier Python 2 versions, the fact remains that Python 2.6 and earlier have reached their official end-of-life and their use should not be encouraged. On Python 3, 3.0, 3.1 and 3.2 have similarly reached end-of-life and no longer receive security support.
  • On Python 3, 3.3 was the first widely-adopted release, and also introduced features (not present in earlier Python 3 releases) which greatly simplify the process of consistently handling strings in both Python 2 and Python 3 within the same codebase.

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.

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 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 colorsys.

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 simply involve working 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 addtional indirection layer of having to instantiate and serialize a color-wrapping object.

Keeping a simple function-based interface also maintains consistency with Python’s built-in 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 <>. Issues and pull requests can both be filed there.