Before:
G['up'] = 3.14159265359j
G['dn'] = 3.14159265359j
After G['up'] += G['dn']:
G['up'] = 6.28318530718j
G['dn'] = 3.14159265359j
After g_up += g_dn:
G['up'] = 9.42477796077j
G['dn'] = 3.14159265359j
After G += G:
G['up'] = 18.8495559215j
G['dn'] = 6.28318530718j