The zc.zk package provides support for registering and discovering services with ZooKeeper. It also provides support for defining services with a tree-based model and syncing the model with ZooKeeper.

The use cases are:

• Register a server providing a service.
• Get the addresses of servers providing a service.
• Get and set service configuration data.
• Model system architecture as a tree.

Important note for zc.zk 1.x users

Version 2 is mostly. but not entirely backward compatible.

Although the goal of version 1 was primarily service registration and discovery, it also provided a high-level ZooKeeper API. Kazoo is a much better high-level interface for ZooKeeper because:

• It isn't based on the buggy ZooKeeper C interface and Python extension.
• It doesn't assume that ephemeral nodes should be reestablished when a session expires and is recreated.

zc.zk 2 uses Kazoo.

This package makes no effort to support Windows. (Patches to support Windows might be accepted if they don't add much complexity.)

You can install this as you would any other distribution. It requires the kazoo Python ZooKeeper interface.

To use the helper API, create a ZooKeeper instance:

>>> import zc.zk
>>> zk = zc.zk.ZooKeeper('zookeeper.example.com:2181')

The ZooKeeper constructor takes a ZooKeeper connection string, which is a comma-separated list of addresses of the form HOST:PORT. It defaults to the value of the ZC_ZK_CONNECTION_STRING environment variable, if set, or '127.0.0.1:2181' if not, which is convenient during development.

You can also pass a kazoo client object, instead of a connection string.

To register a server, use the register method, which takes a service path and the address a server is listing on:

>>> zk.register('/fooservice/providers', ('192.168.0.42', 8080))

register creates a read-only ephemeral ZooKeeper node as a child of the given service path. The name of the new node is (a string representation of) the given address. This allows clients to get the list of addresses by just getting the list of the names of children of the service path.

Ephemeral nodes have the useful property that they're automatically removed when a ZooKeeper session is closed or when the process containing it dies. De-registration is automatic.

When registering a server, you can optionally provide server (node) data as additional keyword arguments to register. By default, the process id is set as the pid property. This is useful to tracking down the server process. In addition, an event is generated, providing subscribers to add properties as a server is being registered. (See Server-registration events.)

Getting the addresses providing a service is accomplished by getting the children of a service node:

>>> addresses = zk.children('/fooservice/providers')
>>> sorted(addresses)
['192.168.0.42:8080']

The children method returns an iterable of names of child nodes of the node specified by the given path. The iterable is automatically updated when new providers are registered:

>>> zk.register('/fooservice/providers', ('192.168.0.42', 8081))
>>> sorted(addresses)
['192.168.0.42:8080', '192.168.0.42:8081']

You can also get the number of children with len:

>>> len(addresses)
2

You can call the iterable with a callback function that is called whenever the list of children changes:

>>> @zk.children('/fooservice/providers')
... def addresses_updated(addresses):
...     print 'addresses changed'
...     print sorted(addresses)
addresses changed
['192.168.0.42:8080', '192.168.0.42:8081']

The callback is called immediately with the children. When we add another child, it'll be called again:

>>> zk.register('/fooservice/providers', ('192.168.0.42', 8082))
addresses changed
['192.168.0.42:8080', '192.168.0.42:8081', '192.168.0.42:8082']

You get service configuration data by getting properties associated with a ZooKeeper node. The interface for getting properties is similar to the interface for getting children:

>>> data = zk.properties('/fooservice')
>>> data['database']
u'/databases/foomain'
>>> data['threads']
1

The properties method returns a mapping object that provides access to node data. (ZooKeeper only stores string data for nodes. zc.zk provides a higher-level data interface by storing JSON strings.)

The properties objects can be called with callback functions and used as function decorators to get update notification:

>>> @zk.properties('/fooservice')
... def data_updated(data):
...     print 'data updated'
...     for item in sorted(data.items()):
...         print '%s: %r' % item
data updated
database: u'/databases/foomain'
favorite_color: u'red'
threads: 1

The callback is called immediately. It'll also be called when data are updated.

You can update properties by calling the update method:

>>> thread_info = {'threads': 2}
>>> data.update(thread_info, secret='123')
data updated
database: u'/databases/foomain'
favorite_color: u'red'
secret: u'123'
threads: 2

You can also set individual properties:

>>> data['threads'] = 1 data updated database: u'/databases/foomain' favorite_color: u'red' secret: u'123' threads: 1

If you call the set method, keys not listed are removed:

>>> data.set(threads= 3, secret='1234') data updated secret: u'1234' threads: 3

Both update and set can take data from a positional data argument, or from keyword parameters. Keyword parameters take precedent over the positional data argument.

Sometimes, you want to get service data, but don't want to watch for changes. If you pass watch=False to properties, Then properties won't track changes. In this case, you can't set callback functions, but you can still update data.

You can describe a ZooKeeper tree using a textual tree representation. You can then populate the tree by importing the representation. Heres an example:

/lb : ipvs
  /pools
    /cms
      # The address is fixed because it's
      # exposed externally
      address = '1.2.3.4:80'
      providers -> /cms/providers
    /retail
      address = '1.2.3.5:80'
      providers -> /cms/providers

/cms : z4m cms
  threads = 3
  /providers
  /databases
    /main
      /providers

/retail : z4m retail
  threads = 1
  /providers
  /databases
    main -> /cms/databases/main
    /ugc
      /providers

This example defines a tree with 3 top nodes, lb and cms, and retail. The retail node has two sub-nodes, providers and databases and a property threads.

The /retail/databases node has symbolic link, main and a ugc sub-node. The symbolic link is implemented as a property named We'll say more about symbolic links in a later section. Thelb,cmsandretailnodes have *types*. A type is indicated by following a node name with a colon and a string value. The string value is used to populate atypeproperty. Types are useful to document the kinds of services provided at a node and can be used by deployment tools to deploy service providers. You can import a tree definition with theimport_treemethod:: >>> zk.import_tree(tree_text) This imports the tree at the top of the ZooKeeper tree. We can also export a ZooKeeper tree:: >>> print zk.export_tree(), /cms : z4m cms threads = 3 /databases /main /providers /providers /fooservice secret = u'1234' threads = 3 /providers /lb : ipvs /pools /cms address = u'1.2.3.4:80' providers -> /cms/providers /retail address = u'1.2.3.5:80' providers -> /cms/providers /retail : z4m retail threads = 1 /databases main -> /cms/databases/main /ugc /providers /providers Note that when we export a tree: - The special reserved top-level zookeeper node is omitted. - Ephemeral nodes are omitted. - Each node's information is sorted by type (properties, then links, - then sub-nodes) and then by name, You can export just a portion of a tree:: >>> print zk.export_tree('/fooservice'), /fooservice secret = u'1234' threads = 3 /providers You can optionally see ephemeral nodes:: >>> print zk.export_tree('/fooservice', ephemeral=True), /fooservice secret = u'1234' threads = 3 /providers /192.168.0.42:8080 pid = 9999 /192.168.0.42:8081 pid = 9999 /192.168.0.42:8082 pid = 9999 We can import a tree over an existing tree and changes will be applied. Let's update our textual description:: /lb : ipvs /pools /cms # The address is fixed because it's # exposed externally address = '1.2.3.4:80' providers -> /cms/providers /cms : z4m cms threads = 4 /providers /databases /main /providers .. -> tree_text and re-import:: >>> zk.import_tree(tree_text) extra path not trimmed: /lb/pools/retail We got a warning about nodes left over from the old tree. We can see this if we look at the tree:: >>> print zk.export_tree(), /cms : z4m cms threads = 4 /databases /main /providers /providers /fooservice secret = u'1234' threads = 3 /providers /lb : ipvs /pools /cms address = u'1.2.3.4:80' providers -> /cms/providers /retail address = u'1.2.3.5:80' providers -> /cms/providers /retail : z4m retail threads = 1 /databases main -> /cms/databases/main /ugc /providers /providers If we want to trim these, we can add atrimoption. This is a little scary, so we'll use the dry-run option to see what it's going to do:: >>> zk.import_tree(tree_text, trim=True, dry_run=True) would delete /lb/pools/retail. If we know we're not trimming things and want to avoid a warning, we can use trim=False: >>> zk.import_tree(tree_text, trim=False) We can see that this didn't trim by using dry-run again: >>> zk.import_tree(tree_text, trim=True, dry_run=True) would delete /lb/pools/retail. We do want to trim, so we use trim=True: >>> zk.import_tree(tree_text, trim=True) >>> print zk.export_tree(), /cms : z4m cms threads = 4 /databases /main /providers /providers /fooservice secret = u'1234' threads = 3 /providers /lb : ipvs /pools /cms address = u'1.2.3.4:80' providers -> /cms/providers /retail : z4m retail threads = 1 /databases main -> /cms/databases/main /ugc /providers /providers Note that nodes containing (directly or recursively) ephemeral nodes will never be trimmed. Also node that top-level nodes are never automatically trimmed. So we weren't warned about the unreferenced top-level nodes in the import. Recursive deletion ================== ZooKeeper only allows deletion of nodes without children. Thedelete_recursivemethod automates removing a node and all of it's children. If we want to remove theretailtop-level node, we can use delete_recursive:: >>> zk.delete_recursive('/retail') >>> print zk.export_tree(), /cms : z4m cms threads = 4 /databases /main /providers /providers /fooservice secret = u'1234' threads = 3 /providers /lb : ipvs /pools /cms address = u'1.2.3.4:80' providers -> /cms/providers Bt default,delete_recursivewon't delete ephemeral nodes, or nodes that contain them:: >>> zk.delete_recursive('/fooservice') Not deleting /fooservice/providers/192.168.0.42:8080 because it's ephemeral. Not deleting /fooservice/providers/192.168.0.42:8081 because it's ephemeral. Not deleting /fooservice/providers/192.168.0.42:8082 because it's ephemeral. /fooservice/providers not deleted due to ephemeral descendent. /fooservice not deleted due to ephemeral descendent. You can use theforceoption to force ephemeral nodes to be deleted. Symbolic links ============== ZooKeeper doesn't have a concept of symbolic links, butzc.zkprovides a convention for dealing with symbolic links. When trying to resolve a path, if a node lacks a child, but has a property with a name ending in' ->', the child will be found by following the path in the property value. Theresolvemethod is used to resolve a path to a real path:: >>> zk.resolve('/lb/pools/cms/providers') u'/cms/providers' In this example, the link was at the endpoint of the virtual path, but it could be anywhere:: >>> zk.register('/cms/providers', '1.2.3.4:5') >>> zk.resolve('/lb/pools/cms/providers/1.2.3.4:5') u'/cms/providers/1.2.3.4:5' Note a limitation of symbolic links is that they can be hidden by children. For example, if we added a real node, at/lb/pools/cms/provioders, it would shadow the link.children,properties, andregisterwill automatically useresolveto resolve paths. When thechildrenandpropertiesare used for a node, the paths they use will be adjusted dynamically when paths are removed. To illustrate this, let's get children of/cms/databases/main:: >>> main_children = zk.children('/cms/databases/main') >>> main_children.path '/cms/databases/main' >>> main_children.real_path '/cms/databases/main' .. test >>> main_properties = zk.properties('/cms/databases/main') >>> main_properties.path '/cms/databases/main' >>> main_properties.real_path '/cms/databases/main'ChildrenandPropertiesobjects have apathattribute that has the value passed to thechildrenorpropertiesmethods. They have areal_pathattribute that contains the path after resolving symbolic links. Let's suppose we want to move the database node to '/databases/cms'. First we'll export it:: >>> export = zk.export_tree('/cms/databases/main', name='cms') >>> print export, /cms /providers Note that we used the exportnameoption to specify a new name for the exported tree. Now, we'll create a databases node:: >>> zk.create('/databases') u'/databases' And import the export:: >>> zk.import_tree(export, '/databases') >>> print zk.export_tree('/databases'), /databases /cms /providers Next, we'll create a symbolic link at the old location. We can use thelnconvenience method:: >>> zk.ln('/databases/cms', '/cms/databases/main') >>> zk.get_properties('/cms/databases') {u'main ->': u'/databases/cms'} Now, we can remove/cms/databases/mainandmain_childrenwill be updated:: >>> zk.delete_recursive('/cms/databases/main') >>> main_children.path '/cms/databases/main' >>> main_children.real_path u'/databases/cms' .. test >>> main_properties.path '/cms/databases/main' >>> main_properties.real_path u'/databases/cms' If we update/databases/cms,main_childrenwill see the updates:: >>> sorted(main_children) ['providers'] >>> _ = zk.delete('/databases/cms/providers') >>> sorted(main_children) [] .. test >>> dict(main_properties) {} >>> zk.properties('/databases/cms').set(a=1) >>> dict(main_properties) {u'a': 1} Symbolic links can be relative. If a link doesn't start with a slash, it's interpreted relative to the node the link occurs in. The special names.and..have their usual meanings. So, in:: /a /b l -> c l2 -> ../c /c /c .. -> relative_link_source >>> zk.import_tree(relative_link_source) >>> zk.resolve('/a/b/l') u'/a/b/c' >>> zk.resolve('/a/b/l2') u'/a/c' >>> zk.delete_recursive('/a') The link at/a/b/lresolves to/a/b/cand/a/b/l2resolves to/a/c. Property links ============== In addition to symbolic links between nodes, you can have links between properties. In our earlier example, both the/cmsand/fooservicenodes hadthreadsproperties:: /cms : z4m cms threads = 4 /databases /main /providers /providers /fooservice secret = u'1234' threads = 3 /providers /lb : ipvs /pools /cms address = u'1.2.3.4:80' providers -> /cms/providers If we wanted/cmsto have the samethreadssettings, we could use a property link:: /cms : z4m cms threads => /fooservice threads /databases /main /providers /providers /fooservice secret = u'1234' threads = 3 /providers /lb : ipvs /pools /cms address = u'1.2.3.4:80' providers -> /cms/providers .. -> property_link_source >>> _ = zk.create('/test-propery-links', '', zc.zk.OPEN_ACL_UNSAFE) >>> zk.import_tree(property_link_source, '/test-propery-links') >>> properties = zk.properties('/test-propery-links/cms') >>> properties['threads =>'] u'/fooservice threads' >>> properties['threads'] 3 >>> zk.import_tree('/cms\n threads => /fooservice\n', ... '/test-propery-links') extra path not trimmed: /test-propery-links/cms/databases extra path not trimmed: /test-propery-links/cms/providers >>> properties['threads =>'] u'/fooservice' >>> properties['threads'] 3 >>> zk.delete_recursive('/test-propery-links') Property links are indicated with=>. The value is a node path and optional property name, separated by whitespace. If the name is ommitted, then the refering name is used. For example, the name could be left off of the property link above. Node deletion ============= If a node is deleted andChildrenorPropertiesinstances have been created for it, and the paths they were created with can't be resolved using symbolic links, then the instances' data will be cleared. Attempts to update properties will fail. If callbacks have been registered, they will be called without arguments, if possible. It would be bad, in practice, to remove a node that processes are watching. Registering a server with a blank hostname ========================================== It's common to use an empty string for a host name when calling bind to listen on all IPv4 interfaces. If you pass an address with an empty host toregisterand `netifaces <http://alastairs-place.net/projects/netifaces/>`_ is installed, then all of the non-local IPv4 addresses [#ifaces]_ (for the given port) will be registered. If there are no non-local interfaces (not connected to network), then the local IPV4 interface will be registered. If netifaces isn't installed and you pass an empty host name, then the fully-qualified domain name, as returned bysocket.getfqdn()will be used for the host. Server-registration events ========================== Whenregisteris called, azc.zk.RegisteringServerevent is emmitted with a properties attribute that can be updated by subscribers prior to creating the ZooKeeper ephemeral node. This allows third-party code to record extra server information. Events are emitted by passing them tozc.zk.event.notify. Ifzope.eventis installed, thenzc.zk.event.notifyis an alias forzope.event.notify, otherwise,zc.zk.event.notifyis an empty function that can be replaced by applications. ZooKeeper Session Management ============================ Kazoo takes care of reestablishing ZooKeeper sessions. Watches created with thechildrenandpropertiesmethods are reestablished when new sessions are established.zc.zkalso recreates ephemeral nodes created viaregister. zookeeper_export script ======================= The `zc.zk` package provides a utility script for exporting a ZooKeeper tree:: $ zookeeper_export -e zookeeper.example.com:2181 /fooservice /fooservice secret = u'1234' threads = 3 /providers /192.168.0.42:8080 pid = 9999 /192.168.0.42:8081 pid = 9999 /192.168.0.42:8082 pid = 9999 .. -> sh >>> command, expected = sh.strip().split('\n', 1) >>> _, command, args = command.split(None, 2) >>> import pkg_resources >>> export = pkg_resources.load_entry_point( ... 'zc.zk', 'console_scripts', command) >>> import sys, StringIO >>> sys.stdout = f = StringIO.StringIO(); export(args.split()) >>> got = f.getvalue() >>> import zc.zk.tests >>> zc.zk.tests.checker.check_output(expected.strip(), got.strip(), 0) True >>> export(['zookeeper.example.com:2181', '/fooservice']) /fooservice secret = u'1234' threads = 3 /providers >>> export(['zookeeper.example.com:2181']) /cms : z4m cms threads = 4 /databases main -> /databases/cms /providers /databases /cms a = 1 /fooservice secret = u'1234' threads = 3 /providers /lb : ipvs /pools /cms address = u'1.2.3.4:80' providers -> /cms/providers >>> export(['zookeeper.example.com:2181', '/fooservice', '-oo']) >>> print open('o').read(), /fooservice secret = u'1234' threads = 3 /providers The export script provides the same features as theexport_treemethod. Use the--helpoption to see how to use it. zookeeper_import script ======================= The `zc.zk` package provides a utility script for importing a ZooKeeper tree. So, for example, given the tree:: /provision /node1 /node2 .. -> file_source >>> with open('mytree.txt', 'w') as f: f.write(file_source) In the filemytree.txt, we can import the file like this:: $ zookeeper_import zookeeper.example.com:2181 mytree.txt /fooservice .. -> sh >>> command = sh.strip() >>> expected = '' >>> _, command, args = command.split(None, 2) >>> import_ = pkg_resources.load_entry_point( ... 'zc.zk', 'console_scripts', command) >>> import_(args.split()) >>> zk.print_tree() /cms : z4m cms threads = 4 /databases main -> /databases/cms /providers /1.2.3.4:5 pid = 9999 /databases /cms a = 1 /fooservice secret = u'1234' threads = 3 /providers /192.168.0.42:8080 pid = 9999 /192.168.0.42:8081 pid = 9999 /192.168.0.42:8082 pid = 9999 /provision /node1 /node2 /lb : ipvs /pools /cms address = u'1.2.3.4:80' providers -> /cms/providers Read from stdin: >>> stdin = sys.stdin >>> sys.stdin = StringIO.StringIO('/x\n/y') >>> import_('-d zookeeper.example.com:2181 - /fooservice'.split()) add /fooservice/x add /fooservice/y >>> sys.stdin = StringIO.StringIO('/x\n/y') >>> import_('-d zookeeper.example.com:2181'.split()) add /x add /y Trim: >>> sys.stdin = StringIO.StringIO('/provision\n/y') >>> import_('-dt zookeeper.example.com:2181 - /fooservice'.split()) would delete /fooservice/provision/node1. would delete /fooservice/provision/node2. add /fooservice/y >>> sys.stdin = stdin The import script provides the same features as theimport_treemethod, with the exception that it provides less flexibility for specifing access control lists. Use the--helpoption to see how to use it. Propery-update script ===================== The `zc.zk` package provides a utility script for updating individual properties:: zookeeper_set_property zookeeper.example.com:2181 /fooservice \ threads=4 debug=True comment='ok' .. -> example >>> example = example.replace('\\', '') >>> args = example.strip().split() >>> set_property = pkg_resources.load_entry_point( ... 'zc.zk', 'console_scripts', args.pop(0)) >>> set_property(args) data updated comment: u'ok' debug: True secret: u'1234' threads: 4 >>> zk.print_tree('/fooservice') /fooservice comment = u'ok' debug = True secret = u'1234' threads = 4 /providers /192.168.0.42:8080 pid = 9999 /192.168.0.42:8081 pid = 9999 /192.168.0.42:8082 pid = 9999 /provision /node1 /node2 The first argument to the script is the path of the node to be updated. Any number of additional arguments of the form:NAME=PYTHONEXPRESSIONare provided to supply updates. If setting strings, you may have to quote the argument, as in "comment='a comment'". Iterating over a tree ===================== Thewalkmethod can be used to walk over the nodes in a tree:: >>> for path in zk.walk(): ... print path / /cms /cms/databases /cms/providers /cms/providers/1.2.3.4:5 /databases /databases/cms /fooservice /fooservice/providers /fooservice/providers/192.168.0.42:8080 /fooservice/providers/192.168.0.42:8081 /fooservice/providers/192.168.0.42:8082 /fooservice/provision /fooservice/provision/node1 /fooservice/provision/node2 /lb /lb/pools /lb/pools/cms /zookeeper /zookeeper/quota >>> for path in zk.walk('/fooservice'): ... print path /fooservice /fooservice/providers /fooservice/providers/192.168.0.42:8080 /fooservice/providers/192.168.0.42:8081 /fooservice/providers/192.168.0.42:8082 /fooservice/provision /fooservice/provision/node1 /fooservice/provision/node2 You can omit ephemeral nodes: >>> for path in zk.walk('/fooservice', ephemeral=False): ... print path /fooservice /fooservice/providers /fooservice/providers/192.168.0.42:8080 /fooservice/providers/192.168.0.42:8081 /fooservice/providers/192.168.0.42:8082 /fooservice/provision /fooservice/provision/node1 /fooservice/provision/node2 You can also get a mutable list of children, which you can mutate: >>> i = zk.walk('/fooservice', children=True) >>> path, children = i.next() >>> path, children ('/fooservice', [u'providers', u'provision']) >>> del children[0] >>> for path in i: ... print path /fooservice/provision /fooservice/provision/node1 /fooservice/provision/node2 Modifications to nodes are reflected while traversing:: >>> for path in zk.walk('/fooservice'): ... print path ... if 'provision' in zk.get_children(path): ... zk.delete_recursive(path+'/provision') /fooservice /fooservice/providers /fooservice/providers/192.168.0.42:8080 /fooservice/providers/192.168.0.42:8081 /fooservice/providers/192.168.0.42:8082 Graph analysis ============== The textual tree representation can be used to model and analyze a system architecturte. You can get a parsed representation of a tree usingzc.zk.parse_treeto parse a text tree representation generated by hand for import, or using theexport_treemethod. :: >>> tree = zc.zk.parse_tree(tree_text) >>> sorted(tree.children) ['cms', 'lb'] >>> tree.children['lb'].properties {'type': 'ipvs'} The demo module,zc.zk.graphvisshows how you might generate system diagrams from tree models. Reference ========= zc.zk.ZooKeeper ---------------zc.zk.ZooKeeper([connection_string[, session_timeout[, wait]]])Return a new instance given a ZooKeeper connection string. The connection string defaults to the value of theZC_ZK_CONNECTION_STRINGenvironment variable, if set, otherwise '127.0.0.1:2181' will be used. If a session timeout (session_timeout) isn't specified, the ZooKeeper server's default session timeout is used. If the connection to ZooKeeper flaps, setting this to a higher value can avoid having clients think a server has gone away, when it hasn't. The downside of setting this to a higher value is that if a server crashes, it will take longer for ZooKeeper to notice that it's gone. Thewaitflag indicates whether the constructor should wait for a connection to ZooKeeper. It defaults to False. If a connection can't be made, azc.zk.FailedConnectexception is raised.children(path)Return a `zc.zk.Children`_ for the path. Note that there is a fair bit of machinery in `zc.zk.Children`_ objects to support keeping them up to date, callbacks, and cleaning them up when they are no-longer used. If you only want to get the list of children once, useget_children.close()Close the ZooKeeper session. This should be called when cleanly shutting down servers to more quickly remove ephemeral nodes.delete_recursive(path[, dry_run[, force[, ignore_if_ephemeral]]])Delete a node and all of it's sub-nodes. Ephemeral nodes or nodes containing them are not deleted by default. To force deletion of ephemeral nodes, supply theforceoption with a true value. Normally, a message is printed if a node can't be deleted because it's ephemeral or has ephemeral sub-nodes. If theignore_if_ephemeraloption is true, the a message isn't printed if the node's path was passed todelete_recursivedirectly. (This is used byimport_treewhen the only nodes that would be trimmed are ephemeral nodes.) The dry_run option causes a summary of what would be deleted to be printed without actually deleting anything.export_tree(path[, ephemeral[, name]])Export a tree to a text representation. path The path to export. ephemeral Boolean, defaulting to false, indicating whether to include ephemeral nodes in the export. Including ephemeral nodes is mainly useful for visualizing the tree state. name The name to use for the top-level node. This is useful when using export and import to copy a tree to a different location and name in the hierarchy. Normally, when exporting the root node,/, the root isn't included, but it is included if a name is given.import_tree(text[, path='/'[, trim[, acl[, dry_run]]]])Create tree nodes by importing a textual tree representation. text A textual representation of the tree. path The path at which to create the top-level nodes. trim Boolean, defaulting to false, indicating whether nodes not in the textual representation should be removed. acl An access control-list to use for imported nodes. If not specified, then full access is allowed to everyone. dry_run Boolean, defaulting to false, indicating whether to do a dry run of the import, without applying any changes.is_ephemeral(path)ReturnTrueif the node atpathis ephemeral,Falseotherwise.ln(source, destination)Create a symbolic link at the destination path pointing to the source path. If the destination path ends with'/', then the source name is appended to the destination.print_tree(path='/')Print the tree at the given path. This is just a short-hand for:: print zk.export_tree(path, ephemeral=True),properties(path, watch=True)Return a `zc.zk.Properties`_ for the path. Note that there is a fair bit of machinery in `zc.zk.Properties`_ objects to support keeping them up to date, callbacks, and cleaning them up when they are no-longer used. If you don't want to track changes, passwatch=False.register(path, address, acl=zc.zk.READ_ACL_UNSAFE, **data)Register a server at a path with the address. An ephemeral child node ofpathwill be created with name equal to the string representation (HOST:PORT) of the given address.addressmust be a host and port tuple.aclis a ZooKeeper access control list. Optional node properties can be provided as keyword arguments.resolve(path)Find the real path for the given path.walk(path)Iterate over the nodes of a tree rooted at path. In addition,ZooKeeperinstances provide shortcuts to the following kazoo client methods:exists,create,delete,get_children,get, andset. zc.zk.Children --------------__iter__()Return an iterator over the child names.__call__(callable)Register a callback to be called whenever a child node is added or removed. The callback is passed the children instance when a child node is added or removed. TheChildreninstance is returned. zc.zk.Properties ---------------- Properties objects provide the usual read-only mapping methods, __getitem__, __len__, etc..set(data=None, **properties)Set the properties for the node, replacing existing data. The data argument, if given, must be a dictionary or something that can be passed to thedictconstructor. Items supplied as keywords take precedence over items supplied in the data argument.update(data=None, **properties)Update the properties for the node. The data argument, if given, must be a dictionary or something that can be passed to a dictionary'supdatemethod. Items supplied as keywords take precedence over items supplied in the data argument.__call__(callable)Register a callback to be called whenever a node's properties are changed. The callback is passed the properties instance when properties are changed. ThePropertiesinstance is returned. Other module attributes ------------------------zc.zk.ZKA convenient aliad forzc.zk.ZooKeeperfor people who hate to type. Testing support --------------- Thezc.zk.testingmodule providessetUpandtearDownfunctions that can be used to emulate a ZooKeeper server. To find out more, use the help function:: >>> import zc.zk.testing >>> help(zc.zk.testing) .. -> ignore >>> import zc.zk.testing .. cleanup >>> zk.close() Change History ============== 2.1.0 (2014-10-20) ================== - Get the default connection string fromZC_ZK_CONNECTION_STRINGif set. 2.0.1 (2014-08-28) ================== - Fixed: ZooKeeper operations (including closing ZooKeeper connections) hung after network failures if ZooKeeper sessions were lost and ephemeral nodes (for registered services) had to be re-registered. - Fixed: Didn't properly handle None values for node data returned by Kazoo 2.0. 2.0.0 (2014-06-02) ================== Final release (identical to 2.0.0a7). We've used this in production for several months. 2.0.0a7 (2014-02-12) -------------------- Fixed: The release missed a zcml file helpful for registering monitoring components. 2.0.0a6 (2014-02-10) -------------------- This release has a number of backward-compatibility changes made after testing some existing client software with the a5 release. - Restored thewaitconstructor flag to keep trying if a connection fails. - Restored therecv_timeoutfor test backward compatibility. - Restored the test handle-management mechanism for test backward-compatibility. - Fixed a bug in the way test machinery used internal handles. - Restored the create_recursive method for backward compatibility. 2.0.0a5 (2014-01-30) -------------------- - Log when sessions are lost and ephemeral nodes are restored. Fixed: Kazoo returns node children as Unicode. zc.zk client applications expect children as returned by the children to have bytes values and they use the values to connect sockets.Childrenobjects returned by zc.zk.children now encode child names using UTF-8. Fixed: zc.zk 2 didn't accept a value of None for session_timeout constructor argument, breaking some old clients. 2.0.0a4 (2014-01-13) -------------------- Fixed: When saving properties in ZooKeeper nodes, empty properties were encoded as empty strings. When Kazoo saves empty strings, it does so in a way that causes the ZooKeeper C client (or at least the Python C binding) to see semi-random data, sometimes including data written previously to other nodes. This can cause havoc when data for one node leaks into another. Now, we save empty properties as'{}'. 2.0.0a3 (2014-01-08) -------------------- - Renamedget_raw_propertiesback toget_properties, for backward compatibility, now that we've decided not to have a separate package. - Addedensure_pathto the testing client. - Updated theZooKeeper.close`` method to allow multiple calls. (Calls after the first have no effect.)

Fixed packaging bug.

Initial version forked from zc.zk 1.2.0