Multiple filter parameters in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of filtering with multiple query parameters

Consider a REST API endpoint that filters products by category and price range using query parameters. What is the output when requesting /products?category=books&min_price=10&max_price=20 if the database contains:

• Book A: category=books, price=15
• Book B: category=books, price=25
• Pen: category=stationery, price=5

Rest API

products = [
  {"name": "Book A", "category": "books", "price": 15},
  {"name": "Book B", "category": "books", "price": 25},
  {"name": "Pen", "category": "stationery", "price": 5}
]

filtered = [p for p in products if p["category"] == "books" and 10 <= p["price"] <= 20]
print(filtered)

A [{'name': 'Pen', 'category': 'stationery', 'price': 5}]

B [{'name': 'Book B', 'category': 'books', 'price': 25}]

C []

D [{'name': 'Book A', 'category': 'books', 'price': 15}]

💡 Hint

Filter by category first, then check price range.

Only 'Book A' matches both category 'books' and price between 10 and 20 inclusive.

🧠 Conceptual

intermediate

Understanding multiple filter parameters in REST APIs

When a REST API endpoint supports multiple filter parameters like ?color=red&size=medium, how are these filters usually combined to select results?

A Filters are combined with AND logic, so results must match all filters.

B Filters are combined with OR logic, so results can match any filter.

C Filters are ignored and all results are returned.

D Filters are combined randomly for each request.

💡 Hint

Think about how multiple conditions narrow down results.

Multiple filter parameters usually narrow results, so they are combined with AND logic.

🔧 Debug

advanced

Identify the error in handling multiple filters

This code snippet tries to filter users by age and city from query parameters but returns incorrect results. What is the error?

Rest API

def filter_users(users, age=None, city=None):
    filtered = users
    if age:
        filtered = [u for u in users if u['age'] == age]
    if city:
        filtered = [u for u in users if u['city'] == city]
    return filtered

users = [
    {'name': 'Alice', 'age': 30, 'city': 'NY'},
    {'name': 'Bob', 'age': 25, 'city': 'LA'},
    {'name': 'Carol', 'age': 30, 'city': 'LA'}
]

result = filter_users(users, age=30, city='LA')
print(result)

A The second filter overwrites the first, so only city filter applies.

B The function returns an empty list because users is empty.

C The function raises a TypeError due to wrong parameter types.

D The function filters correctly and returns both conditions.

💡 Hint

Check how the filtered list is updated after each condition.

Each filter uses the original users list instead of the filtered list, so the second filter overwrites the first.

📝 Syntax

advanced

Syntax error in parsing multiple filter parameters

Which option correctly parses multiple filter parameters from a URL query string in Python?

Rest API

from urllib.parse import parse_qs
query = 'type=fruit&type=vegetable&color=red'
params = parse_qs(query)
print(params)

A {'type': 'vegetable', 'color': 'red'}

B {'type': ['fruit', 'vegetable'], 'color': ['red']}

C SyntaxError: invalid syntax

D {'type': ['fruit'], 'color': ['red']}

💡 Hint

parse_qs returns lists for each key.

parse_qs returns a dictionary where each key maps to a list of values, even if only one value exists.

🚀 Application

expert

Combining multiple filters with optional parameters

You want to build a REST API endpoint that filters orders by optional parameters: status, min_total, and max_total. Which code snippet correctly applies all filters only if parameters are provided?

A

filtered = []
for o in orders:
  if status and o['status'] != status:
    continue
  if min_total and o['total'] < min_total:
    continue
  if max_total and o['total'] > max_total:
    continue
  filtered.append(o)

B

filtered = orders
if status:
  filtered = [o for o in orders if o['status'] == status]
if min_total:
  filtered = [o for o in orders if o['total'] >= min_total]
if max_total:
  filtered = [o for o in orders if o['total'] <= max_total]

C

filtered = orders
if status:
  filtered = [o for o in filtered if o['status'] == status]
if min_total:
  filtered = [o for o in filtered if o['total'] >= min_total]
if max_total:
  filtered = [o for o in filtered if o['total'] <= max_total]

D

filtered = orders
if status:
  filtered = [o for o in filtered if o['status'] != status]
if min_total:
  filtered = [o for o in filtered if o['total'] < min_total]
if max_total:
  filtered = [o for o in filtered if o['total'] > max_total]

💡 Hint

Apply filters step by step on the current filtered list.

Option C correctly filters the list cumulatively, applying each filter only if the parameter is given.