"Structural pattern matching" for Python, part 2 [LWN.net]

"Structural pattern matching" for Python, part 2

Posted Sep 8, 2020 7:21 UTC (Tue) by johill (subscriber, #25196)
In reply to: "Structural pattern matching" for Python, part 2 by ecree
Parent article: "Structural pattern matching" for Python, part 2

You can probably use some more "magic" to make that shorter, something like

  from matching import match, capture

  with match(p) as matches:
    if m := matches((capture.x, capture.y)):
      print("Diagonal at %d" % (m.x, ))
    elif m := matches((0, capture.y)):
      print("X-axis at %d" % (m.y, ))
    elif m := matches((capture.x, capture.y)):
      print("Point at (%d, %d)" % (m.x, m.y))
    else:
      raise ValueError("Not a 2-tuple")
  return Point(*p)

You need something like

class CapturedVar:
  def __init__(self, name):
    self.name = name

class capture:
  def __getattr__(self, name):
    return CapturedVar(name)

and "match(...)" returns an object that is callable; the called method knows about CapturedVar instances and bumps those into the returned MatchedVars object ("m").

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