System Information
Operating system: Darwin-18.7.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 570 OpenGL Engine ATI Technologies Inc. 4.1 ATI-2.11.20

Blender Version
Broken: version: 2.83.0, branch: master, commit date: 2020-06-03 12:23, hash: rB82e3bd4bbb82
Worked: -

Short description of error
Calling bpy.ops.nla.bake() in Python with rotation_mode of the corresponding objects set to QUATERNION, Blender floods the terminal/console with:

quat_prev <Quaternion (w=1.0000, x=0.0000, y=0.0000, z=0.0000)>
quat_prev <Quaternion (w=1.0000, x=0.0000, y=0.0000, z=0.0000)>
quat_prev <Quaternion (w=1.0000, x=0.0000, y=0.0000, z=0.0000)>
quat_prev <Quaternion (w=1.0000, x=0.0000, y=0.0000, z=0.0000)>
quat_prev <Quaternion (w=1.0000, x=0.0000, y=0.0000, z=0.0000)>
[...]

An additional line for each frame that gets baked.
This makes it hard to read other debug information when printing to console.

Exact steps for others to reproduce the error

Partial code used to call bpy.ops.nla.bake():

obj.rotation_mode = 'QUATERNION'
bpy.ops.object.mode_set(mode='POSE')

bpy.ops.nla.bake(
    frame_start=0,
    frame_end=action.frame_range[1],
    step=1,
    only_selected=False,
    visual_keying=True,
    clear_constraints=False,
    clear_parents=False,
    use_current_action=False,
    bake_types=bake_types,
)

There probably is a print command in Blender's bpy.ops.nla.bake() originally used for debugging.