Code Explanation:
1. Importing the itertools module
import itertools
What it does: Imports Python's itertools module, which contains functions for creating iterators for efficient looping.
Why it's needed: We want to use the permutations function to generate all ordered pairs from a list.
2. Creating a list of numbers
nums = [1,2,3,4]
What it does: Creates a list called nums containing the numbers 1, 2, 3, and 4.
Purpose: These are the elements from which we will form permutations.
3. Generating all 2-length permutations
pairs = itertools.permutations(nums, 2)
Function: itertools.permutations(iterable, r)
iterable is the list we want permutations from (nums).
r is the length of each permutation (here 2).
Output: An iterator that produces all ordered pairs of length 2 without repeating the same element.
Example of pairs generated: (1,2), (1,3), (1,4), (2,1), (2,3), etc.
4. Converting the iterator to a list
lst = list(pairs)
What it does: Converts the iterator pairs into a list called lst.
Why: Iterators are “lazy,” meaning they generate items one at a time. Converting to a list allows us to access elements by index.
Resulting list:
[(1,2),(1,3),(1,4),(2,1),(2,3),(2,4),(3,1),(3,2),(3,4),(4,1),(4,2),(4,3)]
5. Printing the first and last elements
print(lst[0], lst[-1])
lst[0]: Accesses the first element of the list → (1,2)
lst[-1]: Accesses the last element of the list → (4,3)
Output:
(1, 2) (4, 3)
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