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Almond Jupyter API

The Almond Jupyter API can be accessed via an instance of almond.api.JupyterApi. Such an instance is created by almond upon start-up. This instance accessible via the kernel variable and in the implicit scope via e.g. implicitly[almond.api.JupyterApi].

A number of higher level helpers rely on it, and provide a more convenient API to display objects.

High level API

Display

A number of classes under almond.display provide an API similar to the IPython display module.

Examples:

// These can be used to display things straightaway
Html("<b>Bold</b>")

// A handle can also be retained, to later update or clear things
val handle = Markdown("""
# title
## section
text
""")

// can be updated in later cells
// (this updates the previous display)
handle.withContent("""
# updated title
## new section
_content_
""").update()

// can be later cleared
handle.clear()

Input

// Request input from user
val result = Input().request()

val result = Input().withPrompt(">>> ").request()

// Request input via password field
val result = Input().withPassword().request()

JupyterAPI

almond.api.JupyterApi allows to

Note that most of its capabilities have more convenient alternatives, see High level API.

Request input

Call stdin on JupyterAPI to request user input, e.g.

kernel.stdin() // clear text input
kernel.stdin(prompt = ">> ", password = true) // password input, with custom prompt

Comm messages

Comm messages are part of the Jupyter messaging protocol. They allow the exchange of arbitrary messages between code running in the front-end (typically JavaScript code) and kernels.

The comm API can be used to receive messages, or send them.

kernel.comm.receiver allows to register a target to receive messages from the front-end, like

val id = java.util.UUID.randomUUID().toString
kernel.publish.html("Waiting", id)

kernel.comm.receiver("A") { data =>
  // received message `data` from front-end
  kernel.publish.updateHtml(s"<code>$data</code>", id)
}

TODO Send to client

Display data

The publish field, of type almond.interpreter.api.OutputHandler, has numerous methods to push display data to the front-end.

The most generic is display, accepting a almond.api.DisplayData.

kernel.publish.display(
  almond.interpreter.api.DisplayData(
    Map(
      // if we set up an extension for application/myapp+json, first element should be picked
      "application/myapp+json" -> """{"a": "A"}""",
      // else, text/html should be displayed
      "text/html" -> "<b>A</b>"
    )
  )
)

OutputHandler also has helper methods to push HTML straightaway.

for (i <- 1 to 10) {
  kernel.publish.html(s"Got item <b>#$i</b>")
  Thread.sleep((200.0 + 200.0 * scala.util.Random.nextGaussian).toLong max 0L)
}

Updatable display data

If passed an id, when pushing some display data, OutputHandler allows to update that data later.

val id = java.util.UUID.randomUUID().toString
kernel.publish.html("Starting", id)

for (i <- 1 to 10) {
  Thread.sleep((200.0 + 200.0 * scala.util.Random.nextGaussian).toLong max 0L)
  kernel.publish.updateHtml(s"Got item <b>#$i</b>", id)
}

kernel.publish.updateHtml("Got all items", id)

Hooks

Hooks allow to pre-process code right before it's executed. Use like

private def runSql(sql: String): String = {
  println("Running query...")
  val fakeResult =
    """<table>
      |<tr>
      |<th>Id</th>
      |<th>Name</th>
      |</tr>
      |<tr>
      |<td>1</td>
      |<td>Tree</td>
      |</tr>
      |<tr>
      |<td>2</td>
      |<td>Apple</td>
      |</tr>
      |</table>
      |""".stripMargin
  fakeResult
}

kernel.addExecuteHook { code =>
  import almond.api.JupyterApi
  import almond.interpreter.api.DisplayData

  if (code.linesIterator.take(1).toList == List("%sql")) {
    val sql = code.linesWithSeparators.drop(1).mkString // drop first line with "%sql"
    val result = runSql(sql)
    Left(JupyterApi.ExecuteHookResult.Success(DisplayData.html(result)))
  }
  else
    Right(code) // just pass on code
}

Such code can be run either in a cell or in a predef file.

Later on, users can run things like

%sql
SELECT id, name FROM my_table
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