Python idiomatic unpacking assignment or False

Question

If function returns a two value list or tuple on success or False on failure, how can I best unpack the return list into two variables while also checking for False?

def get_key_value():
  if (cond != True):
    return False
  return [val1, val2]

# Call it
# How can I also check for False while unpacking?
key, value = get_key_value()

Answer 1

Coverting @Felix Kling's great comment into an answer.

If not being able to find a (key, value) pair indicates some kind of system failure, it would be better to throw an exception. If your failure doesn't really fall into any of the standard exceptions, you should build a new exception type of your own.

The cond != True is better written as not cond. Also it's better to not create a list if it's not necessary.

class DataNotFound(Exception): pass

def get_key_value():
  if not cond:
    raise DataNotFound("Couldn't find it!")
  return val1, val2

try:
    key,value = get_key_value()
except DataNotFound:
    #handle the failure somehow
    key, value = 'ERROR', 'ERROR'