sorted() function in Python - Step-by-Step Execution

Concept Flow - sorted() function

Start with iterable

↓

Call sorted()

↓

Compare elements

↓

Arrange elements in order

↓

Return new sorted list

↓

End

The sorted() function takes an iterable, compares its elements, arranges them in order, and returns a new sorted list.

Execution Sample

Python

numbers = [3, 1, 4, 1]
sorted_numbers = sorted(numbers)
print(sorted_numbers)

This code sorts the list 'numbers' and prints the sorted list.

Execution Table

Step	Action	Iterable State	Comparison	Result
1	Start with numbers = [3, 1, 4, 1]	[3, 1, 4, 1]	N/A	N/A
2	Call sorted(numbers)	[3, 1, 4, 1]	Compare 3 and 1	1 < 3, so 1 comes first
3	Compare 3 and 4	[3, 1, 4, 1]	3 < 4	3 comes before 4
4	Compare 1 and 3	[3, 1, 4, 1]	1 < 3	1 comes before 3
5	Arrange elements	[3, 1, 4, 1]	N/A	[1, 1, 3, 4]
6	Return new sorted list	[3, 1, 4, 1]	N/A	[1, 1, 3, 4]
7	Print sorted_numbers	[3, 1, 4, 1]	N/A	Output: [1, 1, 3, 4]

💡 All elements compared and arranged; sorted() returns new sorted list.

Variable Tracker

Variable	Start	After sorted()	Final
numbers	[3, 1, 4, 1]	[3, 1, 4, 1]	[3, 1, 4, 1]
sorted_numbers	N/A	[1, 1, 3, 4]	[1, 1, 3, 4]

Key Moments - 3 Insights

Does sorted() change the original list?

No, sorted() returns a new sorted list and does not modify the original list 'numbers' as shown in variable_tracker rows 1 and 2.

What type of object does sorted() return?

sorted() always returns a new list, even if the input is another iterable type, as shown in execution_table step 6.

Why do we see multiple comparisons in the execution_table?

sorted() compares elements pairwise to decide their order, which is why steps 2 to 4 show comparisons before arranging the final list.

Visual Quiz - 3 Questions

Look at the execution_table at step 5, what is the arranged list?

A [4, 3, 1, 1]

B [1, 1, 3, 4]

C [3, 1, 4, 1]

D [1, 3, 1, 4]

💡 Hint

Check the 'Result' column at step 5 in the execution_table.

According to variable_tracker, what is the value of 'numbers' after sorted() is called?

A [3, 1, 4, 1]

B [1, 1, 3, 4]

C N/A

D []

💡 Hint

Look at the 'numbers' row in variable_tracker after sorted() call.

If we change 'numbers' to a tuple, what will sorted() return?

A A sorted tuple

B An error

C A sorted list

D The original tuple unchanged

💡 Hint

Recall that sorted() always returns a list regardless of input type.

Concept Snapshot

sorted(iterable) returns a new list with elements sorted in ascending order.
It does not change the original iterable.
Works with any iterable (list, tuple, string).
You can provide key and reverse parameters for custom sorting.
Always returns a list.

Full Transcript

The sorted() function takes an iterable like a list and returns a new list with the elements arranged in ascending order. It compares elements pairwise to decide their order. The original list remains unchanged. The returned object is always a list, even if the input is a tuple or string. This example shows sorting a list of numbers and printing the sorted result.

Practice

1. What does the sorted() function do in Python?

easy

A. Returns a new list with items arranged in order

B. Changes the original list to be sorted

C. Deletes all items from the list

D. Returns the largest item in the list

Solution

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

   The sorted() function creates a new list with the elements arranged in ascending order by default.

2. Step 2: Compare with other options

   It does not change the original list, nor does it delete items or return just the largest item.

3. Final Answer:

   Returns a new list with items arranged in order -> Option A

4. Quick Check:

   sorted() returns new sorted list [OK]

Hint: Remember: sorted() returns a new list, original stays same [OK]

Common Mistakes:

• Thinking sorted() changes the original list
• Confusing sorted() with max() or min()
• Assuming sorted() deletes items

2. Which of the following is the correct syntax to sort a list nums in reverse order using sorted()?

easy

A. sorted(nums, reverse=False)

B. sorted(nums, reverse=0)

C. sorted(nums, reverse=false)

D. sorted(nums, reverse=True)

Solution

1. Step 1: Check the correct parameter for reverse sorting

   The sorted() function uses the keyword argument reverse=True to sort in descending order.

2. Step 2: Validate the parameter type

   The value must be the boolean True, not False, numbers like 0, or undefined names.

3. Final Answer:

   sorted(nums, reverse=True) -> Option D

4. Quick Check:

   Use reverse=True (boolean) for descending sort [OK]

Hint: Use reverse=True (boolean), not False/0/undefined [OK]

Common Mistakes:

• Using reverse=False (sorts ascending)
• Passing falsy numbers like 0
• Using undefined lowercase 'false'

3. What is the output of the following code?

words = ['pear', 'apple', 'orange']
sorted_words = sorted(words, key=len)
print(sorted_words)

medium

A. ['pear', 'apple', 'orange']

B. ['pear', 'apple', 'orange'] sorted by length

C. ['apple', 'orange', 'pear']

D. ['pear', 'apple', 'orange'] sorted by length ascending

Solution

1. Step 1: Understand the key parameter

   The key=len tells sorted() to sort the list by the length of each word.

2. Step 2: Sort words by length

   Lengths: 'pear' (4), 'apple' (5), 'orange' (6). Sorted ascending by length: ['pear', 'apple', 'orange'].

3. Final Answer:

   ['pear', 'apple', 'orange'] -> Option A

4. Quick Check:

   sorted(words, key=len) sorts by length ascending [OK]

Hint: key=len sorts items by their length ascending [OK]

Common Mistakes:

• Confusing sorting by value vs length
• Assuming sorted() changes original list
• Misreading the order of output

4. Find the error in this code snippet:

numbers = [3, 1, 4, 1, 5]
sorted_numbers = sorted(numbers, key='abs')
print(sorted_numbers)

medium

A. sorted() cannot sort numbers

B. Missing parentheses after sorted

C. key argument should be a function, not a string

D. reverse argument is required

Solution

1. Step 1: Check the key argument type

   The key parameter must be a function, like abs, not a string.

2. Step 2: Identify the error

   Here, key='abs' is a string, which causes a TypeError.

3. Final Answer:

   key argument should be a function, not a string -> Option C

4. Quick Check:

   key needs a function, not string [OK]

Hint: Pass function to key, not string name [OK]

Common Mistakes:

• Passing string instead of function to key
• Thinking sorted() can't sort numbers
• Forgetting parentheses in function calls

5. You have a list of tuples representing people and their ages:

people = [('Alice', 30), ('Bob', 25), ('Charlie', 35), ('David', 25)]

How do you use sorted() to sort this list by age ascending, and if ages are equal, by name alphabetically?

hard

A. sorted(people, key=lambda x: (x[0], x[1]))

B. sorted(people, key=lambda x: (x[1], x[0]))

C. sorted(people, key=lambda x: x[1])

D. sorted(people, key=lambda x: x[0])

Solution

1. Step 1: Understand sorting by multiple criteria

   To sort by age first, then by name if ages tie, use a tuple key with age first, then name.

2. Step 2: Write the key function

   The lambda lambda x: (x[1], x[0]) returns a tuple (age, name) for sorting.

3. Step 3: Check other options

   The option sorting by name then age is incorrect. Options sorting by only one field are wrong.

4. Final Answer:

   sorted(people, key=lambda x: (x[1], x[0])) -> Option B

5. Quick Check:

   Use tuple key (age, name) for multi-level sort [OK]

Hint: Use tuple in key: (age, name) for multi-level sorting [OK]

Common Mistakes:

• Sorting by name before age
• Using single key instead of tuple
• Confusing tuple order in key function