Creating dictionary from two sequences in Python - Try It Yourself

Creating dictionary from two sequences

📖 Scenario: You have two lists: one with product names and another with their prices. You want to combine them into a dictionary where each product name is a key and its price is the value.

🎯 Goal: Build a dictionary from two lists using Python, matching each product with its price.

📋 What You'll Learn

Create two lists named products and prices with exact values

Create a variable called product_price_dict to hold the dictionary

Use a Python method to combine products and prices into product_price_dict

Print the product_price_dict to show the final dictionary

💡 Why This Matters

🌍 Real World

Combining two related lists into a dictionary is common when working with data like product catalogs, student grades, or contact information.

💼 Career

This skill is useful for data processing, web development, and automation tasks where you need to organize paired data efficiently.

1

Create the product and price lists

Create a list called products with these exact values: 'apple', 'banana', 'cherry'. Also create a list called prices with these exact values: 0.99, 0.50, 2.00.

Python

# Create the lists products and prices with the exact values
# Your code here

Hint

Use square brackets [] to create lists and separate items with commas.

2

Prepare the dictionary variable

Create an empty dictionary called product_price_dict to store the combined product-price pairs.

Python

products = ['apple', 'banana', 'cherry']
prices = [0.99, 0.50, 2.00]

# Create an empty dictionary called product_price_dict
# Your code here

Hint

Use curly braces {} to create an empty dictionary.

3

Combine the lists into a dictionary

Use the zip function with products and prices to create product_price_dict by converting the zipped pairs into a dictionary.

Python

products = ['apple', 'banana', 'cherry']
prices = [0.99, 0.50, 2.00]

product_price_dict = {}

# Use zip and dict to combine products and prices into product_price_dict
# Your code here

Hint

The zip function pairs items from two lists. Then dict() converts those pairs into a dictionary.

4

Print the dictionary

Print the product_price_dict to display the combined dictionary of products and prices.

Python

products = ['apple', 'banana', 'cherry']
prices = [0.99, 0.50, 2.00]

product_price_dict = dict(zip(products, prices))

# Print the product_price_dict
# Your code here

Hint

Use the print() function to show the dictionary on the screen.

Practice

1. What does the Python function zip() do when used with two sequences?

easy

A. Sorts both sequences in ascending order

B. Adds elements of both sequences together

C. Removes duplicate elements from both sequences

D. Pairs elements from both sequences into tuples

Solution

1. Step 1: Understand the purpose of zip()

   The zip() function pairs elements from two sequences by their positions, creating tuples.

2. Step 2: Recognize the output format

   Each tuple contains one element from each sequence, matched by index.

3. Final Answer:

   Pairs elements from both sequences into tuples -> Option D

4. Quick Check:

   zip() pairs elements = C [OK]

Hint: Remember zip pairs items by position from sequences [OK]

Common Mistakes:

• Thinking zip adds or subtracts elements
• Assuming zip sorts sequences
• Believing zip removes duplicates

2. Which of the following is the correct syntax to create a dictionary from two lists keys and values?

easy

A. dict(zip(keys, values))

B. dict(keys, values)

C. zip(dict(keys), dict(values))

D. dict(keys + values)

Solution

1. Step 1: Understand dict() and zip() usage

   The dict() function can convert an iterable of key-value pairs into a dictionary. zip(keys, values) creates these pairs.

2. Step 2: Check each option's correctness

   dict(zip(keys, values)) correctly uses dict(zip(keys, values)). Others misuse dict() or zip() syntax.

3. Final Answer:

   dict(zip(keys, values)) -> Option A

4. Quick Check:

   dict(zip(keys, values)) = B [OK]

Hint: Use dict(zip(keys, values)) to combine lists into dictionary [OK]

Common Mistakes:

• Trying dict(keys, values) directly
• Using zip on dict() results
• Adding lists inside dict()

3. What is the output of this code?

keys = ['a', 'b', 'c']
values = [1, 2, 3]
result = dict(zip(keys, values))
print(result)

medium

A. {'a': 1, 'b': 2, 'c': 3}

B. {1: 'a', 2: 'b', 3: 'c'}

C. [('a', 1), ('b', 2), ('c', 3)]

D. Error: cannot convert zip object to dict

Solution

1. Step 1: Understand zip pairing

   zip(keys, values) pairs 'a' with 1, 'b' with 2, and 'c' with 3.

2. Step 2: Convert pairs to dictionary

   dict() converts these pairs into key-value pairs in a dictionary.

3. Final Answer:

   {'a': 1, 'b': 2, 'c': 3} -> Option A

4. Quick Check:

   dict(zip(keys, values)) = {'a': 1, 'b': 2, 'c': 3} [OK]

Hint: zip pairs keys and values; dict converts pairs to dictionary [OK]

Common Mistakes:

• Confusing keys and values order
• Expecting list instead of dict
• Thinking zip returns dict directly

4. The following code throws an error. What is the problem?

keys = ['x', 'y']
values = [10, 20, 30]
result = dict(zip(keys, values))
print(result)

medium

A. dict() cannot convert zip object

B. zip() cannot be used with lists

C. There is no error; code runs fine

D. The lists have different lengths causing an error

Solution

1. Step 1: Check list lengths and zip behavior

   zip() pairs elements until the shortest list ends, so no error occurs even if lengths differ.

2. Step 2: Confirm dict() accepts zip object

   dict() can convert the zip object to a dictionary without error.

3. Final Answer:

   There is no error; code runs fine -> Option C

4. Quick Check:

   zip truncates to shortest list; dict accepts zip [OK]

Hint: zip stops at shortest list; no error if lengths differ [OK]

Common Mistakes:

• Assuming zip requires equal length lists
• Thinking dict() can't convert zip
• Expecting error due to list length mismatch

5. Given two lists keys = ['name', 'age', 'city'] and values = ['Alice', '', None], which dictionary comprehension correctly creates a dictionary excluding keys with empty or None values?

hard

A. {k: v for k, v in zip(keys, values)}

B. {k: v for k, v in zip(keys, values) if v}

C. {k: v for k, v in zip(keys, values) if v != ''}

D. {k: v for k, v in zip(keys, values) if v is not None}

Solution

1. Step 1: Understand filtering with dictionary comprehension

   We want to exclude keys where values are empty strings or None. The condition if v filters out falsy values like '' and None.

2. Step 2: Analyze each option's filter

   {k: v for k, v in zip(keys, values) if v} uses if v which excludes both '' and None. {k: v for k, v in zip(keys, values) if v is not None} excludes only None, {k: v for k, v in zip(keys, values) if v != ''} excludes only '', and {k: v for k, v in zip(keys, values)} includes all.

3. Final Answer:

   {k: v for k, v in zip(keys, values) if v} -> Option B

4. Quick Check:

   Filter falsy values with if v = D [OK]

Hint: Use if v to exclude empty or None values in comprehension [OK]

Common Mistakes:

• Filtering only None or only empty string
• Not filtering any values
• Using incorrect syntax for filtering