<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def value_from_ast(value_ast, type, variables=None):
 # type: (Optional[Node], GraphQLType, Optional[Dict[str, Union[List, Dict, int, float, bool, str, None]]]) -> Union[List, Dict, int, float, bool, str, None] """Given a type and a value AST node known to match this type, build a runtime value."""

    if isinstance(type, GraphQLNonNull):
        # Note: we're not checking that the result of coerceValueAST is non-null.
        # We're assuming that this query has been validated and the value used here is of the correct type.
        return value_from_ast(value_ast, type.of_type, variables)

    if value_ast is None:
        return None

    if isinstance(value_ast, ast.Variable):
        variable_name = value_ast.name.value
        if not variables or variable_name not in variables:
            return None

        # Note: we're not doing any checking that this variable is correct. We're assuming that this query
        # has been validated and the variable usage here is of the correct type.
        return variables.get(variable_name)

    if isinstance(type, GraphQLList):
        item_type = type.of_type
        if isinstance(value_ast, ast.ListValue):
            return [
                value_from_ast(item_ast, item_type, variables)
                for item_ast in value_ast.values
            ]

        else:
            return [value_from_ast(value_ast, item_type, variables)]

    if isinstance(type, GraphQLInputObjectType):
        fields = type.fields
        if not isinstance(value_ast, ast.ObjectValue):
            return None

        field_asts = {}

        for field_ast in value_ast.fields:
            field_asts[field_ast.name.value] = field_ast

        obj = {}
        for field_name, field in fields.items():
            if field_name not in field_asts:
                if field.default_value is not None:
                    # We use out_name as the output name for the
                    # dict if exists
                    obj[field.out_name or field_name] = field.default_value

                continue

            field_ast = field_asts[field_name]
            field_value_ast = field_ast.value
            field_value = value_from_ast(field_value_ast, field.type, variables)

            # We use out_name as the output name for the
            # dict if exists
            obj[field.out_name or field_name] = field_value

        return type.create_container(obj)

    assert isinstance(type, (GraphQLScalarType, GraphQLEnumType)), "Must be input type"

    return type.parse_literal(value_ast)