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Persistent filesystem based flags for state and control.

Project description

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, ...) = name
    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")

accesses the flag named "PORTFWD_DISABLE".

Class FlaggedMixin

A mixin class adding flag_* and flagname_* attributes.

This defines the following attributes on instances:

  • flags: the Flags instance providing the flag values.
  • flags_prefix: the prefix for the flags of interest.
  • flagname_name: the full name within .flags of the flag referred to as name. This is .flags_prefix + '_' +name if .flags_prefix is not empty, or just name otherwise.
  • flag_name: the value from .flags of the flag referred to as name. This is a setable attribute with changes propagated to .flags.

Method FlaggedMixin.__init__(self, flags=None, debug=None, prefix=None)

Initialise the mixin.


  • flags: optional parameter; if None defaults to a new default Flags().
  • prefix: optional prefix; if not provided the prefix is derived from the object's .name attribute, or is empty if there is no .name

Class Flags

MRO:,,,,,, FlaggedMixin
A mapping which directly inspects the flags directory.

Method Flags.__init__(self, flagdir=None, environ=None, lock=None, debug=None)

Initialise the Flags instance.


  • flagdir: the directory holding flag state files; if omitted use the value from cs.env.FLAGDIR(environ)
  • environ: the environment mapping to use, default os.environ
  • lock: a Locklike mutex to control multithreaded access; if omitted no locking is down
  • debug: debug mode, default False

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 string values are unchanged.

Other types are converted with bool().

Function uppername(s)

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

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