Yaml Assistant Reference

Note: The Yaml DSL has changed significantly in 0.9.0 in backwards incompatible manner. This documentation is only for version 0.9.0 and later.

This is a reference manual to writing yaml assistants. Yaml assistants use a special DSL defined on this page. For real examples, have a look at assistants in our Github repo.

Why the hell another DSL?
When we started creating DevAssistant and we were asking people who work in various languages whether they’d consider contributing assistants for those languages, we hit the “I’m not touching Python” barrier. Since we wanted to keep the assistants consistent (centralized logging, sharing common functionality, same backtraces, etc...), we created a new DSL. So now we have something that everyone complains about, including Pythonists, which seems to be consistent too ;)

Assistant Roles

For list and description of assistant roles see Assistant Roles.

The role is implied by assistant location in one of the load path directories, as mentioned in Assistants Loading Mechanism.

All the rules mentioned in this document apply to all types of assistants, with exception of sections Modifier Assistants, Preparer Assistants and Task Assistants that talk about specifics of Modifier, resp. Preparer, resp. Task assistants.

Assistant Name

Assistant name is a short name used on command line, e.g. python. Historically, it had to be the only top-level yaml mapping in the file, e.g.:

  fullname: Python
  description: Some verbose description

Since DevAssistant 0.9.0, it is preferred to omit it and just provide the assistant attributes as the top level mapping:

fullname: Python
description: Some verbose description

Assistant name is derived from the filename by stripping the .yaml extension, e.g. assistant python.yaml file is named python.

Assistant Attributes

Assistant attributes form the top level mapping in Yaml file:

fullname: Python

- cl: mkdir -p $name
- log_i: I'm in $name

List of allowed attributes follows (all of them are optional, and have some sort of reasonable default, it’s up to your consideration which of them to use):

a verbose name that will be displayed to user (Python Assistant)
a (verbose) description to show to user (Bla bla create project bla bla)
dependencies (and dependencies_*)
specification of dependencies, see below Dependencies
specification of arguments, see below Args
specification of used files, see below Files
type of the project, see Project Types
run (and run_*)
specification of actual operations, see Run Sections Reference
pre_run and post_run
specification of operations to carry out before/after running main run section, see below Assistants Invocation; follow the rules specified in Run Sections Reference
directory where to take files (templates, helper scripts, ...) from. Defaults to base directory from where this assistant is taken + files. E.g. if this assistant is ~/.devassistant/assistants/crt/path/and/more.yaml, files will be taken from ~/.devassistant/files/crt/path/and/more by default.
absolute or relative path to icon of this assistant (will be used by GUI). If not present, a default path will be used - this is derived from absolute assistant path by replacing assistants by icons and .yaml by .svg - e.g. for ~/.devassistant/assistants/crt/foo/bar.yaml, the default icon path is ~/.devassistant/icons/crt/foo/bar.svg

Assistants Invocation

When you invoke DevAssistant with it will run following assistants sections in following order:

If any of the first three sections fails in any step, DevAssistant will immediately skip to post_run and the whole invocation will be considered as failed (will return non-zero code on command line and show “Failed” in GUI).


Yaml assistants can express their dependencies in multiple sections.

  • Packages from section dependencies are always installed.

  • If there is a section named dependencies_foo, then dependencies from this section are installed iff foo argument is used (either via commandline or via gui). For example:

    $ da python --foo
  • These rules differ for Modifier Assistants

Each section contains a list of mappings dependency type: [list, of, deps]. If you provide more mappings like this:

- rpm: [foo]
- rpm: ["@bar"]

they will be traversed and installed one by one. Supported dependency types:

the dependency list can contain RPM packages or YUM groups (groups must begin with @ and be quoted, e.g. "@Group name")
use / call (these two do completely same, call is obsolete and will be removed in 0.9.0)

installs dependencies from snippet/another dependency section of this assistant/dependency section of superassistant. For example:

- use: foo.dependencies
- use: foo.dependencies_bar # will install dependencies from snippet "foo", section "bar"
- use: self.dependencies_baz # will install dependencies from section "dependencies_baz" of this assistant
- use: super.dependencies # will install dependencies from "dependencies" section of first superassistant that has such section
if, else

conditional dependency installation. For more info on conditions see Run Sections Reference. A very simple example:

- if $foo:
  - rpm: [bar]
- else:
  - rpm: [spam]

Full example:

dependencies: - rpm: [foo, "@bar"]

- rpm: [beans, eggs]
- if $with_spam:
  - use: spam.spamspam
- rpm: ["ham${more_ham}"]

Sometimes your dependencies may get terribly complex - they depend on many parameters, you need to use them dynamically during run, etc. In these cases, consider using Dependencies Command in run section.



In versions starting with 0.9.* and older, the name of the corresponding variable is derived from the argument’s flags (to mimic Python’s argparse behaviour, see below). In newer versions, the variable name is derived from the argument’s name itself.

Arguments are used for specifying commandline arguments or gui inputs. Every assistant can have zero to multiple arguments.

The args section of each yaml assistant is a mapping of arguments to their attributes:

    - -n
    - --name
  help: Name of the project to create.

Available argument attributes:

specifies commandline flags to use for this argument. The longer flag (without the --, e.g. name from --name) will hold the specified commandline/gui value during run section, e.g. will be accessible as $name.
a help string
one of {true,false} - is this argument required?
how many parameters this argument accepts, one of {0, ?,*,+} (e.g. {0, 0 or 1, 0 or more, 1 or more})
a default value (this will cause the default value to be set even if the parameter wasn’t used by user)
one of {store_true, [default_iff_used, value]} - the store_true value will create a switch from the argument, so it won’t accept any parameters; the [default_iff_used, value] will cause the argument to be set to default value value iff it was used without parameters (if it wasn’t used, it won’t be defined at all)
a name of variable to show in help on command line, e.g. with metavar: META, you’ll get a help line --some-arg META <help>.
use / snippet (these two do completely same, snippet is obsolete and will be removed in 0.9.0)
name of the snippet to load this argument from; any other specified attributes will override those from the snippet By convention, some arguments should be common to all or most of the assistants. See Common Assistant Behaviour
if set, the value of this argument will be saved and will reappear in the next launch of devassistant GUI. The attribute string is a key under which the argument value will be stored. The key should be of the form “scope.argname” so that you can either share the value across more assistants or avoid collisions if any other assistant uses an argument with same name but different meaning. The argument values are stored in “~/.devassistant/.config”. It is ignored in command-line interface.

Gui Hints

GUI needs to work with arguments dynamically, choose proper widgets and offer sensible default values to user. These are not always automatically retrieveable from arguments that suffice for commandline. For example, GUI cannot meaningfully prefill argument that says it “defaults to current working directory”. Also, it cannot tell whether to choose a widget for path (with the “Browse ...” button) or just a plain text field.

Because of that, each argument can have gui_hints attribute. This can specify that this argument is of certain type (path/str/bool) and has a certain default. If not specified in gui_hints, the default is taken from the argument itself, if not even there, a sensible “empty” default value is used (home directory/empty string/false). For example:

    - [-p, --path]
      type: path
      default: $(pwd)/foo

If you want your assistant to work properly with GUI, it is good to use gui_hints (currently, it only makes sense to use it for path attributes, as str and bool get proper widgets and default values automatically).


This section serves as a list of aliases of files stored in one of the files dirs of DevAssistant. E.g. if your assistant is assistants/crt/foo/bar.yaml, then files are taken relative to files/crt/foo/bar/ directory. So if you have a file files/crt/foo/bar/spam.foo, you can use:

  spam: &spam
    source: spam.foo

This will allow you to reference the spam.foo file in run section as *spam without having to know where exactly it is located in your installation of DevAssistant. Note, that the Yaml anchor name should be the same as mapping name, e.g. the two spam in spam: &spam should match. This is because of issue 74, that can’t really be reasonably fixed.


Reference for run sections has a separate page: Run Sections Reference.

Modifier Assistants

Modifier assistants are assistants that are supposed to work with already created project. They must be placed under mod subdirectory of one of the load paths, as mentioned in Assistants Loading Mechanism.

There are few special things about modifier assistants:

  • They usually utilize dda_r to read the whole .devassistant file (usually from directory specified by path variable or from current directory). Since version 0.8.0, every modifier assistant has to do this on its own, be it in pre_run or run section. This also allows you to modify non-devassistant projects - just don’t use dda_r.

The special rules below only apply if you use dda_t in pre_run section.

  • They use dependency sections according to the normal rules + they use all the sections that are named according to project_type loaded from .devassistant, e.g. if project_type is [foo, bar], dependency sections dependencies, dependencies_foo and dependencies_foo_bar will be used as well as any sections that would get installed according to specified parameters. The rationale behind this is, that if you have e.g. eclipse modifier that should work for both python django and python flask projects, chance is that they have some common dependencies, e.g. eclipse-pydev. So you can just place these common dependencies in dependencies_python and you’re done (you can possibly place special per-framework dependencies into e.g. dependencies_python_django).
  • By default, they don’t use run section. Assuming that project_type is [foo, bar], they first try to find run_foo_bar, then run_foo and then just run. The first found is used. If you however use cli/gui parameter spam and section run_spam is present, then this is run instead.

Preparer Assistants

Preparer assistants are assistants that are supposed to checkout sources of upstream projects and set up environment for them (possibly utilizing their .devassistant file, if they have one). Preparers must be placed under prep subdirectory of one of the load paths, as mentioned in Assistants Loading Mechanism.

Preparer assistants commonly utilize the dda_dependencies and dda_run commands in run section.

Task Assistants

Task assistants are supposed to carry out arbitrary task that are not related to a specific project. <TODO>