🕵️ Stack Trace Lineup

import re

# Catastrophic backtracking
rx = re.compile(r"(a+)+b")
rx.match("a" * 30 + "X")

# (no error — but THIS HANGS for ~30 seconds.
# The fix: use re.compile with possessive quantifiers or rewrite the regex.)
# match returns None after ~28 seconds

from concurrent.futures import ThreadPoolExecutor

def boom():
    raise ValueError("inside thread")

with ThreadPoolExecutor() as ex:
    fut = ex.submit(boom)
    fut.result()

Traceback (most recent call last):
  File "lineup.py", line 8, in <module>
    fut.result()
    ~~~~~~~~~~^^
concurrent.futures.process.BrokenExecutor: A child process terminated abruptly, the process pool is not usable anymore

import inspect

def f(): pass

sig = inspect.signature(f)
bound = sig.bind()  # no args
bound.apply_defaults()
print(bound.arguments)

# (no error)
OrderedDict()

from functools import singledispatch

@singledispatch
def show(x):
    return f"any: {x}"

@show.register(int)
def _(x): return f"int: {x}"

print(show(True))

# (no error — bool is a subclass of int, so int dispatch wins.
# This is a footgun: True/False go through the int register.)
int: True

import gc
class Node:
    def __init__(self): self.next = None

a = Node(); b = Node()
a.next = b; b.next = a   # cycle
del a; del b
gc.collect()
print(gc.garbage)

# (no error — modern Python's cycle collector handles this)
[]