🕵️ Stack Trace Lineup

def gen():
    yield 1
    return "done"

g = gen()
next(g)
next(g)

Traceback (most recent call last):
  File "lineup.py", line 7, in <module>
    next(g)
    ~~~~^^^
StopIteration: done

from collections import deque
q = deque(maxlen=3)
q.append(1)
q.append(2)
q.append(3)
q.append(4)
print(list(q))

# (no error — but pay attention to what fell off)
[2, 3, 4]

def f(x, /, y):
    return x + y

f(x=1, y=2)

Traceback (most recent call last):
  File "lineup.py", line 4, in <module>
    f(x=1, y=2)
    ~^^^^^^^^^^
TypeError: f() got some positional-only arguments passed as keyword arguments: 'x'

nums = [1, 2, 3, 4, 5]
nums[::-1] = nums
print(nums)

# (no error)
[5, 4, 3, 2, 1]

class A:
    def __init__(self): print("A")

class B(A):
    def __init__(self): print("B")

class C(A):
    def __init__(self): print("C")

class D(B, C): pass

D()

# (no error — the surprise is which __init__ runs)
B