Python snippet for formatting integral file permissions (e.g., as obtained from os.stat) in the familiar rwx layout. Released under CC0, if appropriate.

format_file_permissions.py

# First pass
mode = 500
perms = []
for group_index in range(2, -1, -1):
    group = mode >> (group_index * 3) & 7
    perms.extend([p if group & 1 << 2 - i else '-' for i, p in enumerate(('r', 'w', 'x'))])
print "".join(perms)

# Second pass
mode = 500
perms = []
rwx = ((4, 'r'), (2, 'w'), (1, 'x'))
for group_index in (6, 3, 0):
    group = mode >> group_index & 7
    perms.extend([p if group & i else '-' for i, p in rwx])
print "".join(perms)