Stem Docs

Configuration File Handling

Configuration File Handling

Handlers for text configuration files. Configurations are simple string to string mappings, with the configuration files using the following rules...

For instance...

# This is my sample config
user.name Galen
user.password yabba1234 # here's an inline comment
user.notes takes a fancy to pepperjack cheese
blankEntry.example

msg.greeting
|Multi-line message exclaiming of the
|wonder and awe that is pepperjack!

... would be loaded as...

config = {
  'user.name': 'Galen',
  'user.password': 'yabba1234',
  'user.notes': 'takes a fancy to pepperjack cheese',
  'blankEntry.example': '',
  'msg.greeting': 'Multi-line message exclaiming of the\nwonder and awe that is pepperjack!',
}

Configurations are managed via the Config class. The Config can be be used directly with its get() and set() methods, but usually modules will want a local dictionary with just the configurations that it cares about.

To do this use the config_dict() function. For example...

import getpass
from stem.util import conf, connection

def config_validator(key, value):
  if key == 'timeout':
    # require at least a one second timeout
    return max(1, value)
  elif key == 'endpoint':
    if not connection.is_valid_ipv4_address(value):
      raise ValueError("'%s' isn't a valid IPv4 address" % value)
  elif key == 'port':
    if not connection.is_valid_port(value):
      raise ValueError("'%s' isn't a valid port" % value)
  elif key == 'retries':
    # negative retries really don't make sense
    return max(0, value)

CONFIG = conf.config_dict('ssh_login', {
  'username': getpass.getuser(),
  'password': '',
  'timeout': 10,
  'endpoint': '263.12.8.0',
  'port': 22,
  'reconnect': False,
  'retries': 3,
}, config_validator)

There's several things going on here so lets take it step by step...

Now lets say our user has the following configuration file...

username waddle_doo
password jabberwocky
timeout -15
port 9000000
retries lots
reconnect true
logging debug

... and we load it as follows...

>>> from stem.util import conf
>>> our_config = conf.get_config('ssh_login')
>>> our_config.load('/home/atagar/user_config')
>>> print CONFIG  
{
  "username": "waddle_doo",
  "password": "jabberwocky",
  "timeout": 1,
  "endpoint": "263.12.8.0",
  "port": 22,
  "reconnect": True,
  "retries": 3,
}

Here's an expanation of what happened...

Module Overview:

config_dict - provides a dictionary that's kept in sync with our config
get_config - singleton for getting configurations
uses_settings - provides an annotation for functions that use configurations
parse_enum_csv - helper funcion for parsing confguration entries for enums

Config - Custom configuration
  |- load - reads a configuration file
  |- save - writes the current configuration to a file
  |- clear - empties our loaded configuration contents
  |- add_listener - notifies the given listener when an update occurs
  |- clear_listeners - removes any attached listeners
  |- keys - provides keys in the loaded configuration
  |- set - sets the given key/value pair
  |- unused_keys - provides keys that have never been requested
  |- get - provides the value for a given key, with type inference
  +- get_value - provides the value for a given key as a string
stem.util.conf.config_dict(handle, conf_mappings, handler=None)[source]

Makes a dictionary that stays synchronized with a configuration.

This takes a dictionary of 'config_key => default_value' mappings and changes the values to reflect our current configuration. This will leave the previous values alone if...

  • we don't have a value for that config_key
  • we can't convert our value to be the same type as the default_value

If a handler is provided then this is called just prior to assigning new values to the config_dict. The handler function is expected to accept the (key, value) for the new values and return what we should actually insert into the dictionary. If this returns None then the value is updated as normal.

For more information about how we convert types see our get() method.

The dictionary you get from this is manged by the Config class and should be treated as being read-only.

Parameters:
  • handle (str) -- unique identifier for a config instance
  • conf_mappings (dict) -- config key/value mappings used as our defaults
  • handler (functor) -- function referred to prior to assigning values
stem.util.conf.get_config(handle)[source]

Singleton constructor for configuration file instances. If a configuration already exists for the handle then it's returned. Otherwise a fresh instance is constructed.

Parameters:handle (str) -- unique identifier used to access this config instance
stem.util.conf.uses_settings(handle, path, lazy_load=True)[source]

Provides a function that can be used as a decorator for other functions that require settings to be loaded. Functions with this decorator will be provided with the configuration as its 'config' keyword argument.

Changed in version 1.3.0: Omits the 'config' argument if the funcion we're decorating doesn't accept it.

uses_settings = stem.util.conf.uses_settings('my_app', '/path/to/settings.cfg')

@uses_settings
def my_function(config):
  print 'hello %s!' % config.get('username', '')
Parameters:
  • handle (str) -- hande for the configuration
  • path (str) -- path where the configuration should be loaded from
  • lazy_load (bool) -- loads the configuration file when the decorator is used if true, otherwise it's loaded right away
Returns:

function that can be used as a decorator to provide the configuration

Raises :

IOError if we fail to read the configuration file, if lazy_load is true then this arises when we use the decorator

stem.util.conf.parse_enum(key, value, enumeration)[source]

Provides the enumeration value for a given key. This is a case insensitive lookup and raises an exception if the enum key doesn't exist.

Parameters:
  • key (str) -- configuration key being looked up
  • value (str) -- value to be parsed
  • enumeration (stem.util.enum.Enum) -- enumeration the values should be in
Returns:

enumeration value

Raises :

ValueError if the value isn't among the enumeration keys

stem.util.conf.parse_enum_csv(key, value, enumeration, count=None)[source]

Parses a given value as being a comma separated listing of enumeration keys, returning the corresponding enumeration values. This is intended to be a helper for config handlers. The checks this does are case insensitive.

The count attribute can be used to make assertions based on the number of values. This can be...

  • None to indicate that there's no restrictions.
  • An int to indicate that we should have this many values.
  • An (int, int) tuple to indicate the range that values can be in. This range is inclusive and either can be None to indicate the lack of a lower or upper bound.
Parameters:
  • key (str) -- configuration key being looked up
  • value (str) -- value to be parsed
  • enumeration (stem.util.enum.Enum) -- enumeration the values should be in
  • count (int,tuple) -- validates that we have this many items
Returns:

list with the enumeration values

Raises :

ValueError if the count assertion fails or the value entries don't match the enumeration keys

class stem.util.conf.Config[source]

Bases: object

Handler for easily working with custom configurations, providing persistence to and from files. All operations are thread safe.

Example usage:

User has a file at '/home/atagar/myConfig' with...

destination.ip 1.2.3.4
destination.port blarg

startup.run export PATH=$PATH:~/bin
startup.run alias l=ls

And they have a script with...

from stem.util import conf

# Configuration values we'll use in this file. These are mappings of
# configuration keys to the default values we'll use if the user doesn't
# have something different in their config file (or it doesn't match this
# type).

ssh_config = conf.config_dict('ssh_login', {
  'login.user': 'atagar',
  'login.password': 'pepperjack_is_awesome!',
  'destination.ip': '127.0.0.1',
  'destination.port': 22,
  'startup.run': [],
})

# Makes an empty config instance with the handle of 'ssh_login'. This is
# a singleton so other classes can fetch this same configuration from
# this handle.

user_config = conf.get_config('ssh_login')

# Loads the user's configuration file, warning if this fails.

try:
  user_config.load("/home/atagar/myConfig")
except IOError as exc:
  print "Unable to load the user's config: %s" % exc

# This replace the contents of ssh_config with the values from the user's
# config file if...
#
# * the key is present in the config file
# * we're able to convert the configuration file's value to the same type
#   as what's in the mapping (see the Config.get() method for how these
#   type inferences work)
#
# For instance in this case...
#
# * the login values are left alone because they aren't in the user's
#   config file
#
# * the 'destination.port' is also left with the value of 22 because we
#   can't turn "blarg" into an integer
#
# The other values are replaced, so ssh_config now becomes...
#
# {'login.user': 'atagar',
#  'login.password': 'pepperjack_is_awesome!',
#  'destination.ip': '1.2.3.4',
#  'destination.port': 22,
#  'startup.run': ['export PATH=$PATH:~/bin', 'alias l=ls']}
#
# Information for what values fail to load and why are reported to
# 'stem.util.log'.
load(path=None, commenting=True)[source]

Reads in the contents of the given path, adding its configuration values to our current contents. If the path is a directory then this loads each of the files, recursively.

Changed in version 1.3.0: Added support for directories.

Changed in version 1.3.0: Added the commenting argument.

Changed in version 1.6.0: Avoid loading vim swap files.

Parameters:
  • path (str) -- file or directory path to be loaded, this uses the last loaded path if not provided
  • commenting (bool) -- ignore line content after a '#' if True, read otherwise
Raises :
  • IOError if we fail to read the file (it doesn't exist, insufficient permissions, etc)
  • ValueError if no path was provided and we've never been provided one
save(path=None)[source]

Saves configuration contents to disk. If a path is provided then it replaces the configuration location that we track.

Parameters:

path (str) -- location to be saved to

Raises :
  • IOError if we fail to save the file (insufficient permissions, etc)
  • ValueError if no path was provided and we've never been provided one
clear()[source]

Drops the configuration contents and reverts back to a blank, unloaded state.

add_listener(listener, backfill=True)[source]

Registers the function to be notified of configuration updates. Listeners are expected to be functors which accept (config, key).

Parameters:
  • listener (functor) -- function to be notified when our configuration is changed
  • backfill (bool) -- calls the function with our current values if True
clear_listeners()[source]

Removes all attached listeners.

keys()[source]

Provides all keys in the currently loaded configuration.

Returns:list if strings for the configuration keys we've loaded
unused_keys()[source]

Provides the configuration keys that have never been provided to a caller via config_dict() or the get() and get_value() methods.

Returns:set of configuration keys we've loaded but have never been requested
set(key, value, overwrite=True)[source]

Appends the given key/value configuration mapping, behaving the same as if we'd loaded this from a configuration file.

Changed in version 1.5.0: Allow removal of values by overwriting with a None value.

Parameters:
  • key (str) -- key for the configuration mapping
  • value (str,list) -- value we're setting the mapping to
  • overwrite (bool) -- replaces the previous value if True, otherwise the values are appended
get(key, default=None)[source]

Fetches the given configuration, using the key and default value to determine the type it should be. Recognized inferences are:

  • default is a boolean => boolean
    • values are case insensitive
    • provides the default if the value isn't "true" or "false"
  • default is an integer => int
    • provides the default if the value can't be converted to an int
  • default is a float => float
    • provides the default if the value can't be converted to a float
  • default is a list => list
    • string contents for all configuration values with this key
  • default is a tuple => tuple
    • string contents for all configuration values with this key
  • default is a dictionary => dict
    • values without "=>" in them are ignored
    • values are split into key/value pairs on "=>" with extra whitespace stripped
Parameters:
  • key (str) -- config setting to be fetched
  • object (default) -- value provided if no such key exists or fails to be converted
Returns:

given configuration value with its type inferred with the above rules

get_value(key, default=None, multiple=False)[source]

This provides the current value associated with a given key.

Parameters:
  • key (str) -- config setting to be fetched
  • default (object) -- value provided if no such key exists
  • multiple (bool) -- provides back a list of all values if True, otherwise this returns the last loaded configuration value
Returns:

str or list of string configuration values associated with the given key, providing the default if no such key exists