import subprocess
filename_filter = 'Taumatropio_fiori_e_vaso,_1825_Frame_%d.png'
filename_out    = 'Taumatropio_fiori_e_vaso,_1825.gif'
delays = [max(4, abs(i * i * i) / 10) for i in range(-10, 10)]
flags  = []
for delay in delays:
 flags.append('\\\n -delay %3.0f' % (delay))
 for i_frame in range (1, 2 + 1):
  flags.append('-page 0+0 %s' % (filename_filter % (i_frame)))
command = 'convert %s \\\n -loop 0 -transparent "#030303" "%s"' % (' '.join(flags), filename_out)
print(command)
print((subprocess.Popen(command,stdout=subprocess.PIPE, shell=True).communicate())[0])