Understanding the Output of Python's sort() with a Custom Key Function

Explore how Python's `sort()` function works with a custom key function and understand the output it generates. Learn in simple terms why your list gets sorted in a specific order.
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Understanding the Output of Python's sort() with a Custom Key Function

In the world of Python programming, sorting a list can be done in various ways. A common situation arises when we want to sort a list based not just on the natural order of its elements, but using a custom rule defined by a key function. In this guide, we'll explore a specific code snippet that utilizes such a function and clarify how it affects the sorted output.

The Code at Hand

Let's take a look at the code we want to discuss:

[[See Video to Reveal this Text or Code Snippet]]

Initial Query

Upon running this code, you might wonder: What does this code output? The answer is [50, 65, 23, 82, 100]. But how does the abs function come into play here? Let's break it down step by step.

Understanding the Components

The abs Function

First, let's clarify what the abs function does. The abs function returns the absolute value of a number, which means it transforms negative numbers into positive ones. For example:

abs(8) equals 8

abs(-8) also equals 8

This means abs() always returns a non-negative result.

The Sorting Mechanism

Original List: The original list is [100, 50, 65, 82, 23].

Custom Function: For each element n in the list, myfunc(n) is called to get a sorting key based on the expression abs(n - 50).

Calculating the Sorting Keys

Let's go through the computations that myfunc performs for each element:

For 100: abs(100 - 50) results in 50

For 50: abs(50 - 50) results in 0

For 65: abs(65 - 50) results in 15

For 82: abs(82 - 50) results in 32

For 23: abs(23 - 50) results in 27

Result of Key Calculations

The computed results might be summarized as:

myfunc(100) returns 50

myfunc(50) returns 0 (lowest value)

myfunc(65) returns 15

myfunc(82) returns 32

myfunc(23) returns 27

Final Sorting Order

Based on the computed keys, the sort() function arranges the list in increasing order of the results from myfunc. The lower the result from myfunc, the earlier the number appears in the sorted list. Therefore, the sorted list becomes:

Sorted List: [50, 65, 23, 82, 100]

The final output is a reflection of how closely each number is to 50, with 50 itself being the tightest match (resulted in 0), followed next by 65 (resulted in 15), and so on.

Conclusion

In this post, we delved into how Python's sort() function works with a custom key function. Understanding the role of the abs(n - 50) expression enables us to see how the elements are rearranged based on the proximity to 50. By breaking down the components of the code and explaining the calculations, I hope this post brought clarity to the mechanics behind this functionality.

Feel free to experiment with different custom functions, and observe how they affect the sorting order of your lists!