|
| 1 | +""" |
| 2 | +categories: Core,Classes |
| 3 | +description: Descriptor ``__set_name__`` functions may be called twice or missed if members of the parent class are created or removed in ``__set_name__``. |
| 4 | +cause: The ``__set_name__`` procedure is not isolated from the underlying modify-while-iter sequence hazard of the underlying class ``__dict__``. |
| 5 | +workaround: Avoid ``__set_name__`` implementations that add or remove members from the parent class. |
| 6 | +""" |
| 7 | + |
| 8 | +# This bug is EXTREMELY difficult to demonstrate with only a minimal test case |
| 9 | +# due to the unstable iteration order of a class's namespace. This bug more-or-less |
| 10 | +# _requires_ a stochastic test in order to guarantee it occurs or demonstrate its |
| 11 | +# potential impact with any level of clarity. |
| 12 | + |
| 13 | +import random |
| 14 | +import re |
| 15 | + |
| 16 | +letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" |
| 17 | + |
| 18 | +junk_re = re.compile(r"[A-Z][A-Z][A-Z][A-Z][A-Z]") |
| 19 | + |
| 20 | + |
| 21 | +def junk_fill(obj, n=10): # Add randomly-generated attributes to an object. |
| 22 | + for i in range(n): |
| 23 | + name = "".join(random.choice(letters) for j in range(5)) |
| 24 | + setattr(obj, name, object()) |
| 25 | + |
| 26 | + |
| 27 | +def junk_clear(obj): # Remove attributes added by junk_fill. |
| 28 | + to_del = [name for name in dir(obj) if junk_re.match(name)] |
| 29 | + for name in to_del: |
| 30 | + delattr(obj, name) |
| 31 | + |
| 32 | + |
| 33 | +def junk_sequencer(): |
| 34 | + global runs |
| 35 | + try: |
| 36 | + while True: |
| 37 | + owner, name = yield |
| 38 | + runs[name] = runs.get(name, 0) + 1 |
| 39 | + junk_fill(owner) |
| 40 | + finally: |
| 41 | + junk_clear(owner) |
| 42 | + |
| 43 | + |
| 44 | +class JunkMaker: |
| 45 | + def __set_name__(self, owner, name): |
| 46 | + global seq |
| 47 | + seq.send((owner, name)) |
| 48 | + |
| 49 | + |
| 50 | +runs = {} |
| 51 | +seq = junk_sequencer() |
| 52 | +next(seq) |
| 53 | + |
| 54 | + |
| 55 | +class Main: |
| 56 | + a = JunkMaker() |
| 57 | + b = JunkMaker() |
| 58 | + c = JunkMaker() |
| 59 | + d = JunkMaker() |
| 60 | + e = JunkMaker() |
| 61 | + f = JunkMaker() |
| 62 | + g = JunkMaker() |
| 63 | + h = JunkMaker() |
| 64 | + i = JunkMaker() |
| 65 | + j = JunkMaker() |
| 66 | + k = JunkMaker() |
| 67 | + l = JunkMaker() |
| 68 | + m = JunkMaker() |
| 69 | + n = JunkMaker() |
| 70 | + o = JunkMaker() |
| 71 | + p = JunkMaker() |
| 72 | + q = JunkMaker() |
| 73 | + r = JunkMaker() |
| 74 | + s = JunkMaker() |
| 75 | + t = JunkMaker() |
| 76 | + u = JunkMaker() |
| 77 | + v = JunkMaker() |
| 78 | + w = JunkMaker() |
| 79 | + x = JunkMaker() |
| 80 | + y = JunkMaker() |
| 81 | + z = JunkMaker() |
| 82 | + |
| 83 | + |
| 84 | +seq.close() |
| 85 | + |
| 86 | +for k in letters.lower(): |
| 87 | + print(k, runs.get(k, 0)) |
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