return a absolute path jailed in a rootpath

securejoin.py

import os

"""
return a absolute path jailed in a rootpath
example:
    securejoin('/home/john/', 'path1/../../path2')
    > /home/john/path2
"""
def securejoin(rootpath, path):
    path = os.path.join(path).split('/')
    safe = []
    for i in range(len(path)):
        if path[i] == '' or path[i] == '.':
            continue
        elif path[i] == '..':
            if len(safe) > 0:
                safe.pop()
            else:
                continue
        else:
            safe.append(path[i])
    
    return os.path.join(rootpath, '/'.join(safe))