This is bad practice and not allowed in our code, as for why - see:
http://stackoverflow.com/a/2386740/432509

These kinds of ad-hoc logging functions are useful for development, but for now better not add into releases.

(python has logging module, currently we dont make use of it though, operators can report warnings, otherwise some print can be OK as long as not flooding the output, in that case better comment them and uncomment for development)

If this is called a lot, probably better to get the size once and pass it in. (caller has size anyway)

no need for bpy.context (atm its basically same, but happens to be passed in as an arg)

if speed is a concern, you could cache this info, your getting it twice every time. once to check they exist and again later.

def track_markers(track):
    marker_curr = track.markers.find_frame(frame)
    if marker_curr:
        marker_prev = track.markers.find_frame(frame - 1)
        if marker_prev:
            return track, marker_curr, marker_prev
    return None

relevant_tracks = filter(None, (track_markers(track) for track in clip.tracking.tracks))

... you could convert to a list too if needed list(filter(...))

Better use getattr/setattr here, very similar example:

https://developer.blender.org/diffusion/B/browse/master/release/scripts/startup/bl_operators/rigidbody.py;580bb2621330bdc8d99a92ce8be1856053c5b05d$27

Style - convention here is:

frame_start = IntProperty(
        name="Start Frame",
        description="Start frame for baking",
        min=0, max=300000,
        default=1,
        )

also pep8, so spaces around keyword =

for enums convention here is to use single quotes. Convention is followed only in some places.

This variable isn't used below (referencing clip.tracking.tracks.active still)

Also, could be a bit more verbose track_active, for eg. since blender has lots of different active data.

op name is misleading, This is in fact operator properties, in Blender's code we use the name props

We dont have strict conventions here, but would be inclined not to have both text & checkbox... eg:

pie.prop(
		active,
		"use_normalization",
		text="Normalization",
		icon='CHECKBOX_HLT' if active.use_normalization else 'CHECKBOX_DEHLT',
		)

missing ) :)

in this case prefer to have a class list.

See: https://developer.blender.org/diffusion/BA/browse/master/object_print3d_utils/__init__.py;a00934e26c465da8cccfc129fff97e49c0e2f394$117