def ftrgen(path,**opts):
    """File tree recursion (ftr) that yields all paths."""
    from os import listdir,readlink
    from sys import argv,stdout
    pre='TypeError: '+__name__+'() '
    depth = opts.pop('depth',2**62)
    if opts:
        raise TypeError(pre+'got an unexpected keyword argument '+' '.join([repr(x) for x in opts.keys()]))
    if not isinstance(path,str):
        raise TypeError(pre+'apex path is not a string')
    level = [[path]]
    deep = 0
    while level[0]:
        if level[-1]:
            path = '/'.join([x[0] for x in level])
            yield path
            try:
                readlink(path)
                names = []
            except OSError:
                try:
                    names = sorted(listdir(path))
                except OSError:
                    names = []
                deep += 1
                if deep > depth:
                    names = []
            if names:
                level.append(names)
            else:
                level[-1].pop(0)
            continue
        else:
            level[-1:] = []
            level[-1].pop(0)