Bug report

1. Misleading error message

>>> import struct >>> struct.pack(">Q", -1) Traceback (most recent call last): File "<stdin>", line 1, in <module> struct.error: int too large to convert 

I don't think -1 is that large to convert to ulonglong, so the error message is wrong. The problem is that -1 is not in the range of ulonglong. The current error message is not helpful for users to debug.

Compared to other error messages:

Code

import struct for endianness in "<>": for size in "BHILQ": try: fmt = endianness + size struct.pack(fmt, -1) except struct.error as e: print("Error msg of " + fmt + ":", e) 

stdout

Error msg of <B: ubyte format requires 0 <= number <= 255 Error msg of <H: ushort format requires 0 <= number <= 65535 Error msg of <I: argument out of range Error msg of <L: argument out of range Error msg of <Q: argument out of range Error msg of >B: ubyte format requires 0 <= number <= 255 Error msg of >H: argument out of range Error msg of >I: argument out of range Error msg of >L: argument out of range Error msg of >Q: int too large to convert 

2. Inconsistent error messages when packing into different integral types

See the output above.

A possible solution

I can create a PR to fix the 1st problem. For the 2nd problem, #28178 (comment) and #89197 (comment) said that the inconsistency can be fixed, so I can probably fix this in the same PR.

Your environment

• CPython versions tested on: Python 3.12.0a0 (heads/main:ccab67b, Oct 12 2022, 15:25:20) [GCC 12.2.0] on linux
• Operating system and architecture: Arch Linux 5.19.13.arch1-1, x86-64
• Native endianness: Little-endian

Linked PRs

• gh-98248: Normalizing the error messages in function struct.pack #98252