Dumb umask calculator

umask.py

"""
umask.py - a dumb script that demonstrates how umask(2) works
"""

def umask(default, mask):
  """A umask is the bitwise conjunction of default permissions
    <default> and the bitwise negation of file-creation mode mask <mask>"""
  new = []
  for d, m in zip(default, mask):
    new.append(str(int(d) & ~int(m)))
  return ''.join(new)
  

def file_umask(mask):
  """The default creation permission for files is 0666"""
  return umask('0666', mask)
  
  
def dir_umask(mask):
  """The default creation permission for directories is 0777"""
  return umask('0777', mask)