Update 3. Get Only What You Need, and Fast.md

Author: ortizfram

Introduction to MongoDB in Python/3. Get Only What You Need, and Fast.md

@@ -261,3 +261,44 @@ Possible Answers
 - [x] 5: the second call to limit overrides the first
 - [ ] none: instead, an error is raised
 > reason : You can think of the query parameters as being updated like a dictionary in Python: `d = {'limit': 3}; d.update({'limit': 5}); print(d) will print "{'limit': 5}"`
+
+## 🦍 The first five prizes with quarter shares
+- [x] Save to filter_ the filter document to fetch only prizes with one or more quarter-share laureates, i.e. with a "laureates.share" of "4".
+- [x] Save to projection the list of field names so that prize category, year and laureates' motivations ("laureates.motivation") may be fetched for inspection.
+- [x] Save to cursor a cursor that will yield prizes, sorted by ascending year. Limit this to five prizes, and sort using the most concise specification.
+```py
+from pprint import pprint
+
+# Fetch prizes with quarter-share laureate(s)
+filter_ = {'laureates.share': '4'}
+
+# Save the list of field names
+projection = ['category', 'year', 'laureates.motivation']
+
+# Save a cursor to yield the first five prizes
+cursor = db.prizes.find(filter_, projection).sort('year').limit(5)
+pprint(list(cursor))
+```
+## 🦍 Pages of particle-prized people
+- [x] Complete the function get_particle_laureates that, given page_number and page_size, retrieves a given page of prize data on laureates who have the word "particle" (use $regex) in their prize motivations ("prizes.motivation"). Sort laureates first by ascending "prizes.year" and next by ascending "surname".
+- [x] Collect and save the first nine pages of laureate data to pages.
+```py
+from pprint import pprint
+
+# Write a function to retrieve a page of data
+def get_particle_laureates(page_number=1, page_size=3):
+    if page_number < 1 or not isinstance(page_number, int):
+        raise ValueError("Pages are natural numbers (starting from 1).")
+    particle_laureates = list(
+        db.laureates.find(
+            {"prizes.motivation": {"$regex": "particle"}},
+            ["firstname", "surname", "prizes"])
+        .sort([("prizes.year", 1), ("surname", 1)])
+        .skip(page_size * (page_number - 1))
+        .limit(page_size))
+    return particle_laureates
+
+# Collect and save the first nine pages
+pages = [get_particle_laureates(page_number=page) for page in range(1,9)]
+pprint(pages[0])
+```