Dictionary iteration in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print all keys in the dictionary.

Python

my_dict = {'a': 1, 'b': 2, 'c': 3}
for key in my_dict[1]:
    print(key)

Drag options to blanks, or click blank then click option'

A.keys()

B.items()

C.values()

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using .values() instead of .keys() will give values, not keys.

Using .items() returns key-value pairs, not just keys.

Using .keys() lets you loop through all keys in the dictionary.

2fill in blank

medium

Complete the code to print all values in the dictionary.

Python

my_dict = {'x': 10, 'y': 20, 'z': 30}
for value in my_dict[1]:
    print(value)

Drag options to blanks, or click blank then click option'

A[]

B.values()

C.items()

D.keys()

Attempts:

3 left

💡 Hint

Common Mistakes

Using .keys() will give keys, not values.

Using .items() returns key-value pairs, not just values.

Using .values() lets you loop through all values in the dictionary.

3fill in blank

hard

Fix the error in the code to print keys and values.

Python

my_dict = {'name': 'Alice', 'age': 25}
for key, value in my_dict[1]:
    print(key, value)

Drag options to blanks, or click blank then click option'

A.keys()

B.values()

C[]

D.items()

Attempts:

3 left

💡 Hint

Common Mistakes

Using .keys() or .values() will cause unpacking errors.

Not using any method will cause a runtime error.

Using .items() returns key-value pairs, which can be unpacked in the loop.

4fill in blank

hard

Fill both blanks to create a dictionary of squares for even numbers only.

Python

numbers = [1, 2, 3, 4, 5]
squares = {num: num[1]2 for num in numbers if num [2] 2 == 0}

Drag options to blanks, or click blank then click option'

A**

B%

C//

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of ** will add instead of square.

Using // instead of % will not correctly check even numbers.

The ** operator squares the number, and % checks if the number is even.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase keys and values greater than 10.

Python

data = {'a': 5, 'b': 15, 'c': 20}
result = [1]: [2] for [3], val in data.items() if val > 10}

Drag options to blanks, or click blank then click option'

Ak.upper()

Bval

Ck

Dv

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'v' instead of 'val' causes undefined variable error.

Not using .upper() keeps keys lowercase.

Use k.upper() to make keys uppercase, val for values, and k to unpack keys from items.

Practice

1. What does the following code do?
for key in my_dict:

easy

A. Iterates over the keys of the dictionary

B. Iterates over the values of the dictionary

C. Iterates over the key-value pairs as tuples

D. Raises a syntax error

Solution

1. Step 1: Understand the for loop syntax

   The loop uses for key in my_dict, which by default iterates over dictionary keys.

2. Step 2: Identify what is accessed in each iteration

   Each iteration gives one key from the dictionary, not values or pairs.

3. Final Answer:

   Iterates over the keys of the dictionary -> Option A

4. Quick Check:

   for key in dict = keys [OK]

Hint: for key in dict loops over keys only [OK]

Common Mistakes:

• Thinking it loops over values
• Confusing keys with key-value pairs
• Assuming it raises an error

2. Which of the following is the correct syntax to iterate over keys and values in a dictionary my_dict?

easy

A. for key, value in my_dict.keys():

B. for key, value in my_dict:

C. for key in my_dict.values():

D. for key, value in my_dict.items():

Solution

1. Step 1: Recall dictionary methods for iteration

   To get keys and values, use my_dict.items() which returns key-value pairs.

2. Step 2: Check syntax correctness

   Only for key, value in my_dict.items(): correctly unpacks keys and values.

3. Final Answer:

   for key, value in my_dict.items(): -> Option D

4. Quick Check:

   Use dict.items() for keys and values [OK]

Hint: Use dict.items() to get keys and values together [OK]

Common Mistakes:

• Using my_dict without .items() for key-value pairs
• Trying to unpack keys() or values() which return single elements
• Syntax errors from missing .items()

3. What is the output of this code?

my_dict = {'a': 1, 'b': 2}
for k, v in my_dict.items():
    print(k, v)

medium

A. a 1\nb 2

B. ('a', 1)\n('b', 2)

C. a\nb

D. 1\n2

Solution

1. Step 1: Understand the loop over items()

   The loop unpacks each key-value pair from my_dict.items().

2. Step 2: Analyze the print statement

   It prints the key and value separated by space on each line, so output lines are "a 1" and "b 2".

3. Final Answer:

   a 1\nb 2 -> Option A

4. Quick Check:

   print(k, v) prints key and value separated by space [OK]

Hint: print(k, v) shows key and value separated by space [OK]

Common Mistakes:

• Expecting tuples printed instead of separate values
• Printing only keys or only values
• Confusing output format with list or tuple

4. Find the error in this code:

my_dict = {'x': 10, 'y': 20}
for key, value in my_dict:
    print(key, value)

medium

A. Dictionary keys cannot be unpacked

B. Incorrect print statement syntax

C. Missing .items() after my_dict

D. No error, code runs fine

Solution

1. Step 1: Identify the iteration target

   The loop tries to unpack two variables from my_dict directly, which yields only keys.

2. Step 2: Correct the iteration method

   To unpack key and value, use my_dict.items() instead of just my_dict.

3. Final Answer:

   Missing .items() after my_dict -> Option C

4. Quick Check:

   Use my_dict.items() to unpack key, value [OK]

Hint: Use .items() to unpack key and value in loop [OK]

Common Mistakes:

• Trying to unpack keys only without .items()
• Assuming dict directly yields key-value pairs
• Ignoring error message about unpacking

5. Given the dictionary data = {'a': 0, 'b': 2, 'c': 0, 'd': 4}, which code snippet creates a new dictionary with only keys having non-zero values?

hard

A. new_dict = {k: v for k, v in data if v != 0}

B. new_dict = {k: v for k, v in data.items() if v != 0}

C. new_dict = {k: v for k in data.keys() if data[k] != 0}

D. new_dict = {k: v for v, k in data.items() if v != 0}

Solution

1. Step 1: Understand dictionary comprehension with condition

   We want to keep only items where value is not zero, so use if v != 0 in comprehension.

2. Step 2: Check correct unpacking and syntax

   new_dict = {k: v for k, v in data.items() if v != 0} correctly unpacks key and value from data.items() and filters by value.

3. Final Answer:

   new_dict = {k: v for k, v in data.items() if v != 0} -> Option B

4. Quick Check:

   Use dict.items() and filter with if condition [OK]

Hint: Use dict.items() with if condition in comprehension [OK]

Common Mistakes:

• Forgetting .items() when unpacking key and value
• Swapping key and value in unpacking
• Using keys() without accessing values