python

Use the python resource to execute scripts using the Python interpreter. This resource may also use any of the actions and properties that are available to the execute resource. Commands that are executed with this resource are (by their nature) not idempotent, as they are typically unique to the environment in which they are run. Use not_if and only_if to guard this resource for idempotence.

Syntax

A python resource block executes scripts using Python:

python 'hello world' do
  code <<-EOH
    print "Hello world! From Chef and Python."
    EOH
end

where

• code specifies the command to run

The full syntax for all of the properties that are available to the python resource is:

python 'name' do
  code                       String
  creates                    String
  cwd                        String
  environment                Hash
  flags                      String
  group                      String, Integer
  notifies                   # see description
  path                       Array
  provider                   Chef::Provider::Script::Python
  returns                    Integer, Array
  subscribes                 # see description
  timeout                    Integer, Float
  user                       String, Integer
  umask                      String, Integer
  action                     Symbol # defaults to :run if not specified
end

where

• python is the resource
• name is the name of the resource block
• :action identifies the steps the chef-client will take to bring the node into the desired state
• code, creates, cwd, environment, flags, group, path, provider, returns, timeout, user, and umask are properties of this resource, with the Ruby type shown. See “Properties” section below for more information about all of the properties that may be used with this resource.

Actions

This resource has the following actions:

:nothing

Prevent a command from running. This action is used to specify that a command is run only when another resource notifies it.

:run

Default. Run a script.

Properties

This resource has the following properties:

code

Ruby Type: String

A quoted (” ”) string of code to be executed.

creates

Ruby Type: String

Prevent a command from creating a file when that file already exists.

cwd

Ruby Type: String

The current working directory.

environment

Ruby Type: Hash

A Hash of environment variables in the form of ({"ENV_VARIABLE" => "VALUE"}). (These variables must exist for a command to be run successfully.)

flags

Ruby Type: String

One or more command line flags that are passed to the interpreter when a command is invoked.

group

Ruby Types: String, Integer

The group name or group ID that must be changed before running a command.

ignore_failure

Ruby Types: TrueClass, FalseClass

Continue running a recipe if a resource fails for any reason. Default value: false.

notifies

Ruby Type: Symbol, ‘Chef::Resource[String]’

A resource may notify another resource to take action when its state changes. Specify a 'resource[name]', the :action that resource should take, and then the :timer for that action. A resource may notifiy more than one resource; use a notifies statement for each resource to be notified.

A timer specifies the point during the chef-client run at which a notification is run. The following timers are available:

:delayed

Default. Specifies that a notification should be queued up, and then executed at the very end of the chef-client run.

:immediate, :immediately

Specifies that a notification should be run immediately, per resource notified.

The syntax for notifies is:

notifies :action, 'resource[name]', :timer

path

Ruby Type: Array

An array of paths to use when searching for a command. These paths are not added to the command’s environment $PATH. The default value uses the system path.

Warning

For example:

python 'mycommand' do
  environment 'PATH' => "/my/path/to/bin:#{ENV['PATH']}"
end

provider

Ruby Type: Chef Class

Optional. Explicitly specifies a provider. See “Providers” section below for more information.

retries

Ruby Type: Integer

The number of times to catch exceptions and retry the resource. Default value: 0.

retry_delay

Ruby Type: Integer

The retry delay (in seconds). Default value: 2.

returns

Ruby Types: Integer, Array

The return value for a command. This may be an array of accepted values. An exception is raised when the return value(s) do not match. Default value: 0.

subscribes

Ruby Type: Symbol, ‘Chef::Resource[String]’

A resource may listen to another resource, and then take action if the state of the resource being listened to changes. Specify a 'resource[name]', the :action to be taken, and then the :timer for that action.

A timer specifies the point during the chef-client run at which a notification is run. The following timers are available:

:delayed

Default. Specifies that a notification should be queued up, and then executed at the very end of the chef-client run.

:immediate, :immediately

Specifies that a notification should be run immediately, per resource notified.

The syntax for subscribes is:

subscribes :action, 'resource[name]', :timer

timeout

Ruby Types: Integer, Float

The amount of time (in seconds) a command is to wait before timing out. Default value: 3600.

user

Ruby Types: String, Integer

The user name or user ID that should be changed before running a command.

umask

Ruby Types: String, Integer

The file mode creation mask, or umask.

Guards

A guard property can be used to evaluate the state of a node during the execution phase of the chef-client run. Based on the results of this evaluation, a guard property is then used to tell the chef-client if it should continue executing a resource. A guard property accepts either a string value or a Ruby block value:

• A string is executed as a shell command. If the command returns 0, the guard is applied. If the command returns any other value, then the guard property is not applied. String guards in a powershell_script run Windows PowerShell commands and may return true in addition to 0.
• A block is executed as Ruby code that must return either true or false. If the block returns true, the guard property is applied. If the block returns false, the guard property is not applied.

A guard property is useful for ensuring that a resource is idempotent by allowing that resource to test for the desired state as it is being executed, and then if the desired state is present, for the chef-client to do nothing.

Attributes

The following properties can be used to define a guard that is evaluated during the execution phase of the chef-client run:

not_if

Prevent a resource from executing when the condition returns true.

only_if

Allow a resource to execute only if the condition returns true.

Arguments

The following arguments can be used with the not_if or only_if guard properties:

:user

Specify the user that a command will run as. For example:

not_if 'grep adam /etc/passwd', :user => 'adam'

:group

Specify the group that a command will run as. For example:

not_if 'grep adam /etc/passwd', :group => 'adam'

:environment

Specify a Hash of environment variables to be set. For example:

not_if 'grep adam /etc/passwd', :environment => {
  'HOME' => '/home/adam'
}

:cwd

Set the current working directory before running a command. For example:

not_if 'grep adam passwd', :cwd => '/etc'

:timeout

Set a timeout for a command. For example:

not_if 'sleep 10000', :timeout => 10

Providers

Where a resource represents a piece of the system (and its desired state), a provider defines the steps that are needed to bring that piece of the system from its current state into the desired state.

The chef-client will determine the correct provider based on configuration data collected by Ohai at the start of the chef-client run. This configuration data is then mapped to a platform and an associated list of providers.

Generally, it’s best to let the chef-client choose the provider, and this is (by far) the most common approach. However, in some cases, specifying a provider may be desirable. There are two approaches:

• Use a more specific short name—yum_package "foo" do instead of package "foo" do, script "foo" do instead of bash "foo" do, and so on—when available
• Use the provider property within the resource block to specify the long name of the provider as a property of a resource. For example: provider Chef::Provider::Long::Name

This resource has the following providers:

Chef::Provider::Script, script

When this short name is used, the chef-client will determine the correct provider during the chef-client run.

Chef::Provider::Script::Python, python

The provider for the Python command interpreter.

Examples

None.