hw3-1-remove.py

#!/usr/bin/python
# -*- coding: UTF8 -*-

import pymongo
import sys

# Homework 3.1 · Course M101P
#
# Write a program in the language of your choice that will remove
# the lowest homework score for each student. Since there is a single
# document for each student containing an array of scores, you will
# need to update the scores array and remove the homework.
#
# Note: when run twice, all homework scores will have been removed.

connection = pymongo.MongoClient("mongodb://localhost")
db = connection.school
students = db.students

def remove_lowest_homework_score( scores):
	homework_scores = [score for score in scores if score[u"type"] == u"homework"]
 	lowest = min( [score[u"score"] for score in homework_scores])
 	return [score for score in scores \
 		if ( score[u"type"] != u"homework") \
 		   or( score[u"type"] == u"homework" and score[u"score"] != lowest)]

def update_scores( coll, doc_id, new_scores):
	try:
		coll.update( { "_id": doc_id}, { "$set": { "scores": new_scores }})
	except:
		print "Unexpected error while updating:", sys.exc_info()[ 0]

def main( argv):
	try:
		# All students having a score of type "homework" in their scores array
		cursor = students.find( { 'scores.type': 'homework' })
	except:
		print "Unexpected error while finding:", sys.exc_info()[ 0]

	for doc in cursor:
	 	id = doc[ "_id"]
	 	scores = doc[ "scores"]
	 	updated_scores = remove_lowest_homework_score( scores)
	 	update_scores( students, id, updated_scores)
	 	print "updated doc %s:\n    scores: %s\nnew scores: %s" % ( id, scores, updated_scores)

if __name__ == "__main__":
	main(sys.argv[1:])