input: Write a python function to count the occurrences of a given string in a list.
  assert count_occurrences(['Python', 'Python'], "Python") == 2
  assert count_occurrences(['Python', 'Java', 'Python', 'C++'], "Python") == 2
  assert count_occurrences(['Python', 'Java', 'C++'], "Ruby") == 0
  assert count_occurrences([], "Python") == 0
output: def count_occurrences(lst, target):
      return lst.count(target)