Write a function,

 my_len(mappings) 

that, given a list of mappings representing a dictionary, first creates the corresponding dictionary and then computes the length of that dictionary. Recall that to create a dictionary you need the code

D = {}
for mapping in mappings:
  key = mapping[0]
  value = mapping[1]
  D[key] = value

# at this spot, outside the loop above, it's as if D was the parameter

Paste this code into the space below, then find the number of keys in D. Note that D could have fewer than 5 keys, because the latter mappings can overwrite the earlier ones. In the second example below, 'B' starts off mapped to 2, but then later it's mapped to 3 instead.