• all single dot components of the path must be removed. For example, "foo/./bar" should be normalized to "foo/bar". • all double dots components of the path must be removed, along with their parent directory. For example, "foo/bar/../baz" should be normalized to "foo/baz".

normalize_file_path.py

def normalize_file_path(path):

    #assumptions: valid path does not start with '../' or '/..'

    if path.startswith('../') or path.startswith('/..'):
        return None

    #normalize all the double dots first

    double_dot_index = path.find('/..')
    if double_dot_index > -1:
        #get the parent dir
        parent_dir_index = path.rfind('/', 0, double_dot_index)

        #handle case if parent dir is on 1st level (e.g. foo/../bar) 
        if parent_dir_index == -1:
            parent_dir_index = 0

        #normalize by removing the parent dir & double dots
        path_to_remove = path[parent_dir_index:double_dot_index+3]
        path = path.replace(path_to_remove, '') #may remove multiple occurences but it's ok

        #recurse function passing the modified path
        return normalize_file_path(path)

    #normalize the single dots next
    dot_index = path.find('./')
    if dot_index > -1:
        #normalize by removing the single dot
        path = path.replace(path[dot_index:dot_index+2], '')
        
        #recurse function passing the modified path
        return normalize_file_path(path)

    #path is fully normalized
    return path


paths = []
paths.append('foo/bar/../baz')
paths.append('foo/../bar/../baz')
paths.append('foo/./bar')
paths.append('foo/./bar1/./bar2')
paths.append('/./bar/baz')
paths.append('../foo')
paths.append('/../foo')
paths.append('./foo')
paths.append('/./foo')

for path in paths:
    print '%s :        %s' % (path.ljust(30, ' '), normalize_file_path(path))