Lesser known parts of Python standard library

Re:Lesser known parts of Python standard library – Trickster... by judicious on Thursday September 05, 2024 @11:04AM (#41457315)

Dictionary comprehensions can be very elegant. List and dictionary comprehensions are very powerful and expressive abstractions. In fact, while not good practice you can pretty much write all Python code inside comprehensions including stuff regarding mutation.

This is valid(as in it will run, but highly unidiomatic) code:

quicksort = lambda arr: [pivot:=arr[0], left:= [x for x in arr[1:] if x < pivot], right := [x for x in arr[1:] if x >= pivot], quicksort(left) + [pivot] + quicksort(right)][-1] if len(arr) > 1 else arr

print(quicksort([1, 33, -4, -2, 110, 5, 88]))

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Re:Lesser known parts of Python standard library – Trickster... by hansvm on Thursday September 05, 2024 @02:29PM (#41459237)

Sometimes mutations in comprehensions are very expressive.

  def scan(items, f, initial):
    x = initial
    return (x := f(x, y) for y in items)

There are lots of other short ways to write `scan`, but I don't think any of them map so clearly to a naive definition of what it's supposed to do.

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Re:Lesser known parts of Python standard library – Trickster... by judicious on Thursday September 05, 2024 @03:03PM (#41459529)

That's incredibly clever, generators are underrated. I once challenged my friend to do leetcode problems with only expressions. Here's levenshtein distance, however it's incredibly clunky.

  levenshtein_distance = lambda s1, s2: [matrix := [[0] * (len(s2) + 1) for _ in 
  range(len(s1) + 1)], [
          [
              (matrix[i].__setitem__(j, min(matrix[i-1][j] + 1, matrix[i][j-1] + 
  1, matrix[i-1][j-1] + (0 if s1[i-1] == s2[j-1] else 1))), matrix[i][-1])[1]
              for j in range(1, len(s2) + 1)
         ]
         for i in range(1, len(s1) + 1)
     ], matrix[-1][-1]][-1]

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