🕵️ Stack Trace Lineup

from contextlib import contextmanager

@contextmanager
def tx(conn):
    try:
        yield conn
        conn.commit()
    except Exception:
        conn.rollback()
        raise

with tx(None) as c:
    c.execute("UPDATE users SET x=1")

Traceback (most recent call last):
  File "lineup.py", line 13, in <module>
    c.execute("UPDATE users SET x=1")
    ^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'execute'

from dataclasses import dataclass, field

@dataclass
class Cart:
    items: list = []

c = Cart()

Traceback (most recent call last):
  File "lineup.py", line 5, in <module>
    class Cart:
  File "lineup.py", line 5, in Cart
    items: list = []
ValueError: mutable default <class 'list'> for field items is not allowed: use default_factory

import re
pattern = re.compile(r"(\\d+")
print(pattern.match("123"))

Traceback (most recent call last):
  File "lineup.py", line 2, in <module>
    pattern = re.compile(r"(\\d+")
              ~~~~~~~~~~^^^^^^^^^
re.error: missing ), unterminated subpattern at position 0

import asyncio

async def boom():
    raise ValueError("nope")

async def main():
    return await asyncio.gather(boom(), boom())

asyncio.run(main())

Traceback (most recent call last):
  File "lineup.py", line 9, in <module>
    asyncio.run(main())
    ~~~~~~~~~~~^^^^^^^^
  File "asyncio/runners.py", line 190, in run
    return runner.run(main)
           ~~~~~~~~~~^^^^^^
Task exception was never retrieved
ValueError: nope

from typing import Generic, TypeVar

T = TypeVar("T")

class Box(Generic[T]):
    def __init__(self, v: T):
        self.v = v

b = Box[int](v="hi")
print(b.v + 1)

Traceback (most recent call last):
  File "lineup.py", line 10, in <module>
    print(b.v + 1)
          ~~~~^~~
TypeError: can only concatenate str (not "int") to str