Print element from a specific position in the list

Your function is not returning any results, you need to call the return at the end of the function by passing the month number -1 , -1 is array starts counting at 0 instead of 1

def how_many_days(month_number):
  """Returns the number of days in a month.
  WARNING: This function doesn't account for leap years!
  """
  days_in_month = [31,28,31,30,31,30,31,31,30,31,30,31]
  return days_in_month[month_number - 1]

#todo: return the correct value
# This test case should print 31, the number of days in the eighth month, August
print(how_many_days(8))

There are two errors in your code:

For your code to work you need to put return in the function and arrange the indentation and as python starts in 0 you need to return the number of the month - 1, see:

def how_many_days(month_number):
    days_in_month = [31,28,31,30,31,30,31,31,30,31,30,31]
    return days_in_month[month_number-1];
# This test case should print 31, the number of days in the eighth month, August

print(how_many_days(8))

See working at Ideone .

 def how_many_days(month_number):

   """Returns the number of days in a month.
      WARNING: This function doesn't account for leap years!
   """

   days_in_month = [31,28,31,30,31,30,31,31,30,31,30,31]

   return days_in_month[month_number]          
print(how_many_days(7));

That's right.