Python - difference between '../../' and '/../../' when they are concatenated to a path

scnzzh: ~/aaa >cat zzh1.py
import os.path

print(os.path.dirname(__file__))
abs_file_dir = os.path.abspath(os.path.dirname(__file__))
print(abs_file_dir)
a = abs_file_dir + '../../'
print(a)
print(os.path.abspath(a))
scnzzh: ~/aaa >cat zzh2.py
import os.path

print(os.path.dirname(__file__))
abs_file_dir = os.path.abspath(os.path.dirname(__file__))
print(abs_file_dir)
a = abs_file_dir + '/../../'
print(a)
print(os.path.abspath(a))
scnzzh: ~/aaa >python zzh1.py

/home/scnzzh/aaa
/home/scnzzh/aaa../../
/home/scnzzh
scnzzh: ~/aaa >python /home/scnzzh/aaa/zzh1.py
/home/scnzzh/aaa
/home/scnzzh/aaa
/home/scnzzh/aaa../../
/home/scnzzh
scnzzh: ~/aaa >python /home/scnzzh/aaa/zzh2.py
/home/scnzzh/aaa
/home/scnzzh/aaa
/home/scnzzh/aaa/../../
/home