Is it possible to set condition to empty parameter in cerberus?

Question

I want to set conditional validate for empty parameter. For example:

schema = {
'param1': {'type': 'string', empty: False, required:True, 'allowed': ['One', 'Two']},
'param2': {'type': 'string', empty: False, required:True}
}

I need that empty parameter in param2 determined by the condition:

If param1 == 'One' =>> empty in param2 = True else False

I tried like that: 'param2': {'type': 'string', empty: {'if': {'param1': 'One'}, 'then': True, 'else': False}, required:True}

But get error: [{'empty': ['must be of boolean type']}]

Of course, it because empty wait for boolean type.

But if there are some solution for this option?

Answer 1

It's not exactly what you want, but the only interactions between fields that cerberus allows are excludes and dependencies. You can imitate an if statement such as if value == "One" then exclude "param2" else require "param2" like this:

"param1": {
  "allowed": ["One", "Two"],
  "oneof": [
    {
      "allowed": ["One"],  # condition
      "excludes": ["param2"]  # then rule
    },
    {
      "forbidden": ["One"],  # inverse condition
      "dependencies": ["param2"]  # else rule
    }
  ]
}

Logically the schema translates to

given: p <- param1 has value of "One", q <- exclude param2, r <- require param2

then: (p and q) xor (not p and r) <=> if p then q else r