# First lets import our Maya command library
from maya import cmds

# Then we import our file. In this case I'm using a hardcoded value
# But notice the returnNewNodes parameter that tells it to give us back any imported nodes
# This may contain nodes we don't want
# So we'll need to shorten it down
nodes = cmds.file('C:/Users/dhruv/Documents/maya/controllerLibrary/bigdonut.ma',
                  i=True, returnNewNodes=True)

# We need to find all the objects that are shapes
# We use ls to list the nodes we got, and to make sure we only get the shapes
shapes = cmds.ls(nodes, shapes=True, shortNames=True)

# We'll have an empty list to get the controllers
controllers = []

# Then lets loop through this list
for shape in shapes:
    # We want to ignore any cameras so we check the type
    if cmds.objectType(shape) == 'camera':
        # If it's a camera then continue on to the next item
        continue
    # Then we need to find the transform.
    # So we list its' parent to find it
    parent = cmds.listRelatives(shape, parent=True)[0]

    # Then we add the parent transform to the controllers list
    controllers.append(parent)

# Finally lets print out the controllers to see if we got it right
print controllers