Convert function into a nested list comprehension (Python)

Question

Can anyone convert the below function into a list compressions please!

 def something(x,y):

  result = []
  for i in x:
    for j in y:
      if i['username'] == j['username']:
       result.append(j)
    if i['username'] != result[len(result)-1]['username']:
      result.append(i)

  return result

This is best I could come up with but it is not correct.

result = [user for user in users for contact in contacts if contact['username'] == user['username']]

Thank you for any help.

Answer 1

Since what if i['username'] != result[len(result)-1]['username']: result.append(i) is really doing is to append i when there is nothing in y found to match the username of i (because if there was any match in the y loop the last item in result would have the same username as i), you can make the inner loop a sub-list and use the or operator to default to [i] if the sub-list is empty, and finally use nested list comprehension to flatten the list:

result = [a for s in [[j for j in y if i['username'] == j['username']] or [i] for i in x] for a in s]

Or if you prefer the variable names in your latter code example:

result = [a for s in [[contact for contact in contacts if user['username'] == contact['username']] or [user] for user in users] for a in s]