**π‘ Problem Formulation:** Python developers often need to filter data structures based on specific criteria. For instance, suppose you have a list of tuples, and you want to extract only those tuples where every element consists of exactly ‘k’ digits. The input could be `[ (123, 45, 6), (789, 12), (34, 5678, 90) ]`

, and for `k = 2`

, the desired output would be `[(789, 12), (34, 90)]`

. This article explains five methods to perform this task effectively in Python.

## Method 1: Using List Comprehension and the `all()`

Function

This method utilizes list comprehension – a concise way to create lists in Python – combined with the `all()`

function, which checks whether all elements in an iterable satisfy a particular condition. Specifically, we check if all elements in a tuple are integers with exactly ‘k’ digits by converting them to strings and checking their length.

Here’s an example:

tuples = [(123, 45, 6), (789, 12), (34, 5678, 90)] k = 2 result = [t for t in tuples if all(len(str(e)) == k for e in t)] print(result)

Output:

[(789, 12), (34, 90)]

This code snippet filters the list of tuples, keeping only those tuples where each element’s string representation has a length equal to ‘k’. List comprehension and the `all()`

function make this method both powerful and succinct.

## Method 2: Using the `filter()`

Function and a Custom Predicate

The `filter()`

function applies a predicate to each element of an iterable and returns an iterator yielding only those elements for which the predicate is True. By defining a custom function that checks for ‘k’ digit elements within a tuple, we can filter out the desired tuples effectively.

Here’s an example:

def is_k_digits(num, k): return len(str(num)) == k def filter_tuples(tuples, k): return list(filter(lambda x: all(is_k_digits(elem, k) for elem in x), tuples)) tuples = [(123, 45, 6), (789, 12), (34, 5678, 90)] k = 2 print(filter_tuples(tuples, k))

Output:

[(789, 12), (34, 90)]

The code defines a helper function to determine if a number has ‘k’ digits and a filter function to apply this predicate across each tuple in the list. While this method is more verbose than using a list comprehension, it clearly separates the concerns and can be more readable for complex conditions.

## Method 3: Using a For Loop

A traditional for loop offers full control over the iteration process. This method iterates through each tuple and each element within, collecting only those tuples that fulfill the ‘k’ digit condition. This approach is straightforward and easy to understand, especially for those new to Python.

Here’s an example:

tuples = [(123, 45, 6), (789, 12), (34, 5678, 90)] k = 2 filtered_tuples = [] for t in tuples: if all(len(str(element)) == k for element in t): filtered_tuples.append(t) print(filtered_tuples)

Output:

[(789, 12), (34, 90)]

The for loop checks each tuple individually and appends it to the result list if it meets the condition. Although not as compact as a comprehension or high-order function, it is arguably more explicit and great for those who prefer a more structured approach.

## Method 4: Using NumPy Arrays

For those working with numerical data, NumPy is a powerful library that offers array operations and vectorized functions. This method converts each tuple into a NumPy array, then applies a vectorized comparison to find tuples where all elements have ‘k’ digits.

Here’s an example:

import numpy as np def extract_k_digit_tuples(tuples, k): return [t for t in tuples if np.all(np.floor(np.log10(np.abs(t)) + 1) == k)] tuples = [(123, 45, 6), (789, 12), (34, 5678, 90)] k = 2 print(extract_k_digit_tuples(tuples, k))

Output:

[(789, 12), (34, 90)]

This snippet leverages NumPy for its efficient array processing capabilities. It uses a mathematical approach to check the number of digits, which can be faster for large datasets but might be less intuitive for beginners or for those not familiar with NumPy and its operations.

## Bonus One-Liner Method 5: Using Generator Expressions and the `sum()`

Function

Generator expressions are like list comprehensions but they don’t hold the entire output in memory. Paired with the `sum()`

function, we can count the number of tuples that have elements with ‘k’ digits, offering a memory-efficient alternative.

Here’s an example:

tuples = [(123, 45, 6), (789, 12), (34, 5678, 90)] k = 2 valid_tuples = sum(1 for t in tuples if all(len(str(num)) == k for num in t)) print(valid_tuples)

Output:

2

Here, the generator expression iterates through the list of tuples and for each tuple that satisfies the condition, 1 is added to the sum. This one-liner is a memory-efficient way to count the tuples with all elements having ‘k’ digits, though it doesnβt give the actual tuples.

## Summary/Discussion

**Method 1:**List Comprehension with`all()`

. Strengths: Concise and efficient. Weaknesses: Can become complex with more intricate conditions.**Method 2:**Using`filter()`

With a Custom Predicate Function. Strengths: Clear separation of logic, good readability. Weaknesses: Slightly more verbose and may be slower than a comprehension.**Method 3:**Traditional For Loop. Strengths: Explicit, straightforward logic. Weaknesses: More verbose, potentially less performant with large data sets.**Method 4:**Using NumPy Arrays. Strengths: Efficient, fast for large data sets. Weaknesses: Requires NumPy, can be complex for those unfamiliar with it.**Bonus Method 5:**Generator Expression with`sum()`

. Strengths: Memory efficient. Weaknesses: Only counts valid tuples, doesn’t retrieve them.