input: Write a python function to generate a whole population for a genetic algorithm.
  assert len(generate_population()) == 20
  assert all(len(individual) == 2 for individual in generate_population())
  assert all(-1 <= gene <= 1 for individual in generate_population() for gene in individual)
output: import random
  
  def generate_population():
      population = []
      for _ in range(20):
          individual = [random.uniform(-1, 1), random.uniform(-1, 1)]
          population.append(individual)
      return population