This library provides functions which take in RoboFab objects (RFonts or their children) and converts any cubic curves to quadratic. The most useful function is probably fonts_to_quadratic:

from robofab.world import OpenFont
from cu2qu.rf import fonts_to_quadratic
thin_font = OpenFont('MyFont-Thin.ufo')
bold_font = OpenFont('MyFont-Bold.ufo')
fonts_to_quadratic(thin_font, bold_font)

Interpolation compatibility is guaranteed during conversion. If it's not needed, converting one font at a time may yield more optimized results:

for font in [thin_font, bold_font]:
    fonts_to_quadratic(font)

Some fonts may need a different error threshold than the default (0.0025 em). This can also be provided by the caller:

fonts_to_quadratic(thin_font, bold_font, max_err_em=0.005)

for font in [thin_font, bold_font]:
    fonts_to_quadratic(font, max_err_em=0.001)

fonts_to_quadratic can print a string reporting the number of curves of each length. For example fonts_to_quadratic(font, dump_report=True) may print something like:

3: 1000
4: 2000
5: 100

meaning that the font now contains 1000 curves with three points, 2000 with four points, and 100 with five. Given multiple fonts, the function will report the total counts across all fonts. You can also accumulate statistics between calls by providing your own report dictionary:

stats = {}
for font in [thin_font, bold_font]:
    fonts_to_quadratic(font, report=stats)
# "stats" will report combined statistics for both fonts

See the source for functions which operate on glyphs, segments, or just several points. FontCollection classes are also exposed, which allow access into multiple fonts simultaneously and may be generally useful.