Day 2 of Hanukkah at Anvil

Build a web app for each night of Hanukkah, with nothing but Python!

A cornucopia of options

It’s the second night of Chanukah: time for an argument. How do you spell Hanukka?

In today’s app, we provide you with a bounty of transliterations of חֲנוּכָּה‎, for both your enjoyment and fury.

How is the front end made?

We get started by choosing the ‘Hello San Francisco’ style when creating a new app, and choosing the ‘Standard’ theme for our app page. We replace the header.jpg asset with a suitably wintery image so that our header shows something a little more seasonal than the sweeping skyline of San Fran, and then we’re ready to start building the UI!

We add the title, the button (called spelling_button) and a label (called spelling_label) below that which will eventually display the spelling. However, we don’t want that spelling label - and its default text - to be visible before the user hits the button, so in the Form’s startup code, we make sure to hide that label.

    class Form1(Form1Template):
    def __init__(self, **properties):
        self.spelling_label.visible = False # hide the label

Now, we want to make something happen when the button is clicked, so we set its event handler for the click event.

  def spelling_button_click(self, **event_args):
    """This method is called when the button is clicked"""
    self.spelling_label.visible = True # show the label
    self.spelling_label.text ='get_random_spelling')

This code means that when the button is clicked, a server function called get_random_spelling will be called, and its return value will be shown in the spelling_label. Great! Now we need to actually write that server function.

How is the back end made?

We make a new Server Module to house our get_random_spelling function, and decorate our function with the @anvil.server.callable decorator so that we can call it from the client.

def get_random_spelling():
  spelling = "{chet}a{nun}u{kaf}a{he}".format(
  special_spellings = random.random_sample()
  if special_spellings < 0.02:
    if random.random_sample() < 0.01:
      spelling = "Just use the Hebrew."
      spelling = "Janice"
  return spelling

def get_letter_spelling(letter):
  spellings_dict = {
    'chet': {'spellings': ['H', 'Ch','Ḥ', 'X', 'Kh'], 'chances': [0.45, 0.35, 0.15, 0.04, 0.01]},
    'nun': {'spellings': ['n', 'nn', 'nnnnn'], 'chances': [0.5, 0.45, 0.05]},
    'kaf': {'spellings': ['k', 'kk', 'ck'], 'chances': [0.5, 0.45, 0.05]},
    'he': {'spellings': ['h', '', 'hhhhhhh'], 'chances': [0.7, 0.27, 0.03]}
  table = spellings_dict[letter]
  spelling = random.choice(table['spellings'], p=list(table['chances']))
  return spelling

The get_letter_spelling function define a table of probabilities for each letter’s transliterations, using the numpy.random.choice function. The choice function creates a discrete random variable with the given probabilities. So, for chet, we’ve defined the following:

  • 45% chance it’ll come out as H
  • 35% chance it’ll come out as Ch
  • 15% chance it’ll come out as
  • 4% chance it’ll come out as X
  • 1% chance it’ll come out as Kh

Then, for each letter, it returns a spelling choice and we substitute that back into the base string "{chet}a{nun}u{kaf}a{he}".

The following snippet adds a couple of extra, special options:

  special_spellings = random.random_sample()
  if special_spellings < 0.02:
    if special_spellings < 0.01:
      spelling = "Just use the Hebrew."
      spelling = "Janice"

random.random_sample() generates a random float in the interval [0, 1). If it’s less than 0.02, a 2% chance, then we get a ‘special spelling’ - one that didn’t quite fit into the schema we defined above. There’s a 1% chance each of getting Janice or Just use the Hebrew. as your ‘spelling’ - see how many times it takes for you to get them to pop up on the app!

Once we’re done generating a spelling, it gets passed back to the client code and displayed there: the spelling_button_click function sets the spelling_label’s visibility to True, and sets the text to be the spelling we just got from the server.

That’s it!

And that’s it! Go forth and generate some spellings!

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