format_stride_for_width example in API docs doesn't work

[stuaxo]

The example on this page https://pythonhosted.org/cairocffi/api.html causes an exception:

from cairocffi import ImageSurface
stride = ImageSurface.stride_for_width(format, width)
data = bytearray(stride * height)
surface = ImageSurface(format, width, height, data, stride)

## -- End pasted text --
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AttributeError                            Traceback (most recent call last)
<ipython-input-2-e39a39a18953> in <module>()
      1 from cairocffi import ImageSurface
----> 2 stride = ImageSurface.stride_for_width(format, width)
      3 data = bytearray(stride * height)
      4 surface = ImageSurface(format, width, height, data, stride)

AttributeError: type object 'ImageSurface' has no attribute 'stride_for_width'

[SimonSapin]

Good catch, thanks!