brewer2mpl

Common errors

• ValueError: zero length field name in format

  cause This error specifically occurred in Python 2.6 due to a change in string formatting syntax. It was encountered when `brewer2mpl` used `{:>02}` which is not supported in Python 2.6.
  fix Upgrade to a newer Python 2.x version (2.7+) or Python 3.x. If stuck on Python 2.6, manually edit `brewer2mpl.py` (line 151) to replace `{:>02}` with `{0:>02}`.

• KeyError: ('Invalid color map or type', 'NonExistentMap', 'Qualitative', 5)

  cause This error occurs when `brewer2mpl.get_map()` is called with an invalid color map name, an incorrect type (e.g., 'Qualitative' when the map is 'Sequential'), or a number of colors not available for that specific map/type combination. ColorBrewer2 maps have specific names, types, and a limited range of available color counts (e.g., 3-12 colors).
  fix Always verify the correct map name, type (case-sensitive 'Sequential', 'Diverging', 'Qualitative'), and the available number of colors by checking the ColorBrewer2.org website or using `brewer2mpl.print_maps()` to list available options.

Warnings

• deprecated The `brewer2mpl` library is no longer actively maintained or updated. Its development ceased in 2014, and it has been officially superseded by the `Palettable` library. Users are strongly encouraged to migrate to `Palettable` for ongoing support, new features, and broader palette options.
  Fix: Migrate to `Palettable`: `pip install palettable`. Update import statements (e.g., `from palettable.colorbrewer.qualitative import Set2_7` instead of `brewer2mpl.get_map('Set2', 'Qualitative', 7)`).
• gotcha When working with Matplotlib, ensure you use the correct color representation from a `BrewerMap` object. `bmap.colors` provides RGB as 0-255 integer triplets, while `bmap.mpl_colors` provides RGB as 0-1 float triplets, which is the standard expected by Matplotlib functions for discrete colors. `bmap.mpl_colormap` provides a `matplotlib.colors.LinearSegmentedColormap` object for continuous usage.
  Fix: For discrete color lists in Matplotlib, use `bmap.mpl_colors`. For a continuous colormap object, use `bmap.mpl_colormap`. Avoid using `bmap.colors` directly with Matplotlib functions that expect normalized values, as this will lead to incorrect color rendering.

Install

• pip install brewer2mpl Install stable version

Imports

• brewer2mpl

  import brewer2mpl

• get_map
  wrong:

  bmap = brewer2mpl.get_map('Set1', 5)

  correct:

  bmap = brewer2mpl.get_map('Set1', 'Qualitative', 5)

  The `get_map` function requires three arguments: map name, map type ('Sequential', 'Diverging', or 'Qualitative'), and the number of colors.
• sequential

  from brewer2mpl.sequential import Blues

  Direct access to color maps is available via `sequential`, `diverging`, and `qualitative` modules, which contain dictionaries of `BrewerMap` objects keyed by the number of colors.

Quickstart

This quickstart demonstrates how to fetch a named qualitative color map, access its Matplotlib-compatible RGB colors (0-1 range), and print relevant information. The commented-out Matplotlib plotting code shows a simple way to visualize the retrieved colors.

import brewer2mpl
import matplotlib.pyplot as plt

# Get a qualitative color map named 'Set2' with 7 colors
bmap = brewer2mpl.get_map('Set2', 'Qualitative', 7)

# Access colors as 0-1 RGB triplets for Matplotlib
colors_for_mpl = bmap.mpl_colors

print(f"Color map name: {bmap.name}")
print(f"Number of colors: {bmap.number}")
print(f"Matplotlib compatible colors (0-1 RGB): {colors_for_mpl}")

# Example of using colors in a Matplotlib plot (if matplotlib is installed)
# plt.figure(figsize=(7, 1))
# for i, color in enumerate(colors_for_mpl):
#     plt.barh(0, 1, left=i, color=color)
# plt.axis('off')
# plt.title('Brewer2mpl Set2 Qualitative (7 colors)')
# plt.show()