This is an example for the library Fisica for Processing in Python.

CircleMutualAttraction.pyde

"""
 CircleMutualAttraction (v2.3.8)
 by Speykious (2017-Jun-27)
 mod GoToLoop (2017-Jun-29)

 https://Forum.Processing.org/two/discussion/23226/
 new-python-example-for-the-fisica-library#Item_2

 https://Gist.GitHub.com/GoToLoop/1861619991354ed7d063026658270689
"""

# from processing.core import PVector as Vec
Vec = __pvector__

add_library('fisica')

Fisica.init(this)
world = FWorld(gravity=(0, 0))

MIN_DIAM, MAX_DIAM, BOLD = 10, 50, 1.5
FILL, STROKE, BG = 0xffFFFF00, 0xffFF0000, 0xff0000FF
ATTRIBS = FILL, STROKE, BOLD

FPS, FPS_RATE, FORCE, SMOOTH = 60, 30, 1000, 3
MAX_FRAMES = 50 * FPS_RATE

TITLE = 'Balls: %02d  -  Frame: %04d  -  FPS: %02.f'
RENDERER = FX2D

def setup():
    size(600, 400, RENDERER)
    smooth(SMOOTH); frameRate(FPS); colorMode(RGB)
    addBall()


def draw():
    fc = frameCount
    fc < MAX_FRAMES and not fc % FPS_RATE and addBall()
    titleInfo()

    attraction()
    world.step()

    background(BG)
    world.draw()


def titleInfo():
    info = len(balls), frameCount, frameRate
    this.surface.title = TITLE % info


def addBall(attribs=ATTRIBS):
    x = random(MAX_DIAM, width  - MAX_DIAM)
    y = random(MAX_DIAM, height - MAX_DIAM)
    d = round(random(MIN_DIAM, MAX_DIAM))

    fc = FCircle(d, restitution=0, friction=0)
    fc.setPosition(x, y)
    fc.fillColor, fc.strokeColor, fc.strokeWeight = attribs

    world.add(fc)
    world.step(0)

    global balls, ballsNoTail
    balls = world.bodies
    ballsNoTail = balls[:-1]


def attraction(f=FORCE, v1=Vec(), v2=Vec(), i=0):
    for a in ballsNoTail:
        v1.set(a.x, a.y)
        i += 1

        for b in balls[i:]:
            v2.set(b.x, b.y).sub(v1).div(v2.mag()**2).mult(f)
            a.addForce(v2.x, v2.y)