cs.app.flag 20181109

Persistent filesystem based flags for state and control.

Filesystem visible boolean flags for control and status, allowing easy monitoring of services or other status, and control by flag management for programmes which also monitor the flags.

The flags are expressed as individual files with uppercase names in a common directory ($HOME/var/flags by default); an empty or missing file is "false" and a nonempty file is "true".

The Flags class provides easy Pythonic access to this directory. It presents as a modifiable mapping whose keys are the flag names:

  flags = Flags()
  flags['UNTOPPOST'] = True

There is also a FlaggedMixin class providing convenient methods and attributes for maintaining a collection of flags associated with some object with flag names prefixed by the object's .name attribute uppercased and with an underscore appended:

  class SvcD(...,FlaggedMixin):
    def __init__(self, name, ...)
      self.name = name
      FlaggedMixin.__init__(self)
      ...
    def disable(self):
      self.flag_disable = True
    def restart(self):
      self.flag_restart = True
    def _restart(self):
      self.flag_restart = False
      ... restart the SvcD ...

so that an object set up as:

  svcd = SvcD("portfwd")
  print(svcd.flag_disable)

accesses the flag named "PORTFWD_DISABLE".

Class FlaggedMixin

A mixin class adding flag_* and flagname_* attributes.

Class Flags

MRO: collections.abc.MutableMapping, collections.abc.Mapping, collections.abc.Collection, collections.abc.Sized, collections.abc.Iterable, collections.abc.Container, FlaggedMixin
A mapping which directly inspects the flags directory.

Function lowername(s)

Lowercase letters, transmute '_' to '-'. Note: NOT the reverse of uppername.

Function main(argv=None)

Main program: inspect or modify flags.

Function main_flagset(argv=None, stdin=None)

Main program for "flagset" command.

Class PolledFlags

MRO: builtins.dict
A mapping which maintains a dict of the current state of the flags directory and updates it regularly.

This allows an application to consult the flags very frequently without hammering the filesystem.

Function truthy(value)

Decide whether a value is considered true.

Strings are converted to:

• '0': False
• '1': True
• 'true': True (case insensitive)
• 'false': False (case insensitive)
• Other values are unchanged.

Other types are converted with bool().

Function uppername(s)

Uppercase letters, transmute some characters to '_' or '__'.