Write a Python code to sort a dictionary by a specific key.
numbers = {
 '1': 50,
 '2': 60,
 '3': 20,
 '4': 70
}
numbers = {
 '1': 50,
 '2': 60,
 '3': 20,
 '4': 70
}

sorted_dictionary = sorted(numbers.items(), key=lambda x: x[1])
print(sorted_dictionary)