Appending a list into a list. I'm having issues. Challenge task 3/4 "num_teachers"/"stats"

# The dictionary will be something like:
# {'Jason Seifer': ['Ruby Foundations', 'Ruby on Rails Forms', 'Technology Foundations'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#
# Often, it's a good idea to hold onto a max_count variable.
# Update it when you find a teacher with more classes than
# the current count. Better hold onto the teacher name somewhere
# too!
#
# Your code goes below here.

def most_classes(teacher_dict):
  big_num = 0
  big_teacher = ''
  for teacher in teacher_dict:
    class_num = len(teacher_dict[teacher])
    if (class_num > big_num):
      big_num = class_num
      big_teacher = teacher
  return big_teacher

def num_teachers(teacher_dict):
  teach = 0
  for teacher in teacher_dict:
    teach += 1
  return teach

def stats(teacher_dict):
  stat = []
  for teacher in teacher_dict:
    stat.append([teacher,len(teacher_dict)[teacher]])
  return stat