sceptre.resolvers package

class sceptre.resolvers.CustomYamlTagBase(argument=None, stack=None)

Bases: object

A base class for custom Yaml Elements (i.e. hooks and resolvers).

This base class takes care of common functionality needed by subclasses: | * logging setup (associated with stacks) | * Creating unique clones associated with individual stacks (applied recursively down to all | resolvers in the argument) | * On-stack-connect setup that might be needed once connected to a Stack (applied recursively down to | all resolvers in the argument) | * Automatically resolving resolvers in the argument when accessing self.argument

property argument: Any

This is the resolver or hook’s argument.

This property will resolve all nested resolvers inside the argument, but only if this instance has been associated with a Stack.

Resolving nested resolvers will result in their values being replaced in the dict/list they were in with their resolved value, so we won’t have to resolve them again.

Any resolvers that “resolve to nothing” (i.e. return None) will be removed from the dict/list they were in.

If this property is accessed BEFORE the instance has a stack, it will return the raw argument value. This is to safeguard any __init__() behaviors from triggering resolution prematurely.

Return type

Any

clone_for_stack(stack)

Obtains a clone of the current object, setup and ready for use for a given Stack instance.

Return type

TypeVar(Self)

logger = <Logger sceptre.resolvers (WARNING)>

setup()

This method is called when the object is connected to a Stack instance. Implementation of this method in subclasses can be used to do any initial setup of the object.

exception sceptre.resolvers.RecursiveResolve

Bases: Exception

class sceptre.resolvers.ResolvableContainerProperty(name, placeholder_type=PlaceholderType.explicit)

Bases: ResolvableProperty

This is a descriptor class used to store an attribute that may CONTAIN Resolver objects. Resolvers will be resolved upon access of this property. When resolvers are resolved, they will be replaced in the container with their resolved value, in order to avoid redundant resolutions.

Supports nested dictionary and lists.

Parameters

name (str) – Attribute suffix used to store the property in the instance.

class ResolveLater(instance, name, key, resolution_function)

Bases: object

Represents a value that could not yet be resolved but can be resolved in the future.

assign_value_to_stack(stack, value)

Assigns a COPY of the specified value to the stack instance. This method copies the value rather than directly assigns it to avoid bugs related to shared objects in memory.

Parameters

• stack (Stack) – The stack to assign the value to

• value (Union[dict, list]) – The value to assign

get_resolved_value(stack, stack_class)

Obtains the resolved value for this property. Any resolvers that resolve to None will have their key/index removed from their dict/list where they are. Other resolvers will have their key/index’s value replace with the resolved value to avoid redundant resolutions.

Parameters

• stack (Stack) – The Stack instance to obtain the value for

• stack_class (Type[Stack]) – The class of the Stack instance.

Return type

TypeVar(T_Container, bound= Union[dict, list])

Returns

The fully resolved container.

class sceptre.resolvers.ResolvableProperty(name, placeholder_type=PlaceholderType.explicit)

Bases: ABC

This is an abstract base class for a descriptor used to store an attribute that have values associated with Resolver objects.

Parameters

• name (str) – Attribute suffix used to store the property in the instance.

• placeholder_type – The type of placeholder that should be returned, when placeholders are allowed, when a resolver can’t be resolved.

abstract assign_value_to_stack(stack, value)

Implement this method to assign the value to the resolvable property.

abstract get_resolved_value(stack, stack_class)

Implement this method to return the value of the resolvable_property.

Return type

Any

resolve_resolver_value(resolver)

Returns the resolved parameter value.

If the resolver happens to raise an error and placeholders are currently allowed for resolvers, a placeholder will be returned instead of reraising the error.

Parameters

resolver (Resolver) – The resolver to resolve.

Return type

Any

Returns

The resolved value (or placeholder, in certain circumstances)

class sceptre.resolvers.ResolvableValueProperty(name, placeholder_type=PlaceholderType.explicit)

Bases: ResolvableProperty

This is a descriptor class used to store an attribute that may BE a single Resolver object. If it is a resolver, it will be resolved upon access of this property. When resolved, the resolved value will replace the resolver on the stack in order to avoid redundant resolutions.

Parameters

name (str) – Attribute suffix used to store the property in the instance.

assign_value_to_stack(stack, value)

Assigns the value to the Stack instance passed, setting up and cloning the value if it is a Resolver.

Parameters

• stack (Stack) – The Stack instance to set the value on

• value (Any) – The value to set

get_resolved_value(stack, stack_class)

Gets the fully-resolved value from the property. Resolvers will be replaced on the stack instance with their resolved value to avoid redundant resolutions.

Parameters

• stack (Stack) – The Stack instance to obtain the value from

• stack_class (Type[Stack]) – The class of the Stack instance

Return type

Any

Returns

The fully resolved value

class sceptre.resolvers.Resolver(argument=None, stack=None)

Bases: CustomYamlTagBase

Resolver is an abstract base class that should be subclassed by all Resolvers.

raise_invalid_argument_error(message, from_=None)

abstract resolve()

An abstract method which must be overwritten by all inheriting classes. This method is called to retrieve the final desired value. Implementation of this method in subclasses must return a suitable object or primitive type.

Submodules

sceptre.resolvers.environment_variable module

class sceptre.resolvers.environment_variable.EnvironmentVariable(*args, **kwargs)

Bases: Resolver

Resolver for shell environment variables.

Parameters

argument (str) – Name of the environment variable to return.

resolve()

Retrieves the value of a named environment variable.

Returns

Value of the environment variable.

Return type

str

sceptre.resolvers.file_contents module

class sceptre.resolvers.file_contents.FileContents(*args, **kwargs)

Bases: Resolver

Resolver for the contents of a file.

Parameters

argument (str) – Absolute path to file.

resolve()

Retrieves the contents of a file at a given absolute file path.

Returns

Contents of file.

Return type

str

sceptre.resolvers.stack_output module

class sceptre.resolvers.stack_output.StackOutput(*args, **kwargs)

Bases: StackOutputBase

Resolver for retrieving the value of a Stack output within the current Sceptre StackGroup. Adds the target Stack to the dependencies of the Stack using the Resolver.

Parameters

argument (str in the format "<stack name>::<output key>") – The Stack name and output name to get.

resolve()

Retrieves the value of an output of an internal Stack.

Returns

The value of the Stack output.

Return type

str

setup()

Adds dependency to a Stack.

class sceptre.resolvers.stack_output.StackOutputBase(*args, **kwargs)

Bases: Resolver

A abstract base class which provides methods for getting Stack outputs.

class sceptre.resolvers.stack_output.StackOutputExternal(*args, **kwargs)

Bases: StackOutputBase

Resolver for retrieving the value of an output of any Stack within the current Sceptre stack_group’s account and region.

Parameters

argument (str in the format "<full stack name>::<output key>") – The Stack name and output name to get.

resolve()

Retrieves the value of CloudFormation output of the external Stack

Returns

The value of the Stack output.

Return type

str