What is the `ExceptionTable` in the output of `dis`? Question: In python3.13, when I try to disassemble [i for i in range(10)], the result is as below: >>> import dis >>> >>> dis.dis(‘[i for i in range(10)]’) 0 RESUME 0 1 LOAD_NAME 0 (range) PUSH_NULL LOAD_CONST 0 (10) CALL 1 GET_ITER LOAD_FAST_AND_CLEAR 0 (i) SWAP …
Where is the giant cpython switch case statement moved? Question: Not sure if it’s off topic but don’t know any better place to ask. In cpython there was a very giant switch case statement for executing each opcode. This switch case previously was placed in the _PyEval_EvalFrameDefault function. Here is the link. The switch case …
Raising exception in init causes SystemError: returned a result with an error set in Python C API Question: I am using pytest to test my own Python C extension module. I am trying to check if the TypeError occurs properly when an argument of invalid type is input to the __init__ method. The method implementation …
sys.getrefcount() returning very large reference counts Question: In CPython 3.11, the following code returns very large reference counts for some objects. It seems to follow pre-cached objects like integers -5 to 256, but CPython 3.10 does not: Python 3.11.2 (tags/v3.11.2:878ead1, Feb 7 2023, 16:38:35) [MSC v.1934 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" …
Why is b.pop(0) over 200 times slower than del b[0] for bytearray? Question: Letting them compete three times (a million pops/dels each time): from timeit import timeit for _ in range(3): t1 = timeit(‘b.pop(0)’, ‘b = bytearray(1000000)’) t2 = timeit(‘del b[0]’, ‘b = bytearray(1000000)’) print(t1 / t2) Time ratios (Try it online!): 274.6037053753368 219.38099365582403 252.08691226683823 …
Sphinx: Autodocs for classes inheriting from base classes implemented in C Question: I am running into an error/warning when inheriting from collections.deque. Sphinx complains: utils.py:docstring of utils.Test.count:1: WARNING: py:class reference target not found: integer — return number of occurrences of value For this example, utils.py only contains from collections import deque class Test(deque): pass My …
Does a bitwise "and" operation prepend zeros to the binary representation? Question: When I use bitwise and operator(&) with the number of 1 to find out if a number x is odd or even (x & 1), does the interpreter change the binary representation of 1 according to the binary representation of x? For example: …
Why PyList_Append is called each time a list is evaluated? Question: I’m working with CPython3.11.0a3+. I added a break point at PyList_Append and modified the function to stop when the newitem is a dict. The original function: int PyList_Append(PyObject *op, PyObject *newitem) { if (PyList_Check(op) && (newitem != NULL)) return app1((PyListObject *)op, newitem); PyErr_BadInternalCall(); return …
How are small sets stored in memory? Question: If we look at the resize behavior for sets under 50k elements: >>> import sys >>> s = set() >>> seen = {} >>> for i in range(50_000): … size = sys.getsizeof(s) … if size not in seen: … seen[size] = len(s) … print(f"{size=} {len(s)=}") … s.add(i) …
Why sum function is slower if the 'start' argument is an instance of custom class? Question: I was playing around with sum function and observed the following behaviour. case 1: source = """ class A: def __init__(self, a): self.a = a def __add__(self, other): return self.a + other; sum([*range(10000)], start=A(10)) """ import timeit print(timeit.timeit(stmt=source)) As …
