core.py

Pablo Galindo and Łukasz Langa
  • 5.0 (17)
  • TECH NEWS
  • UPDATED BIWEEKLY

We talk about Python internals, because we work on Python internals. We joke about stuff, because we’re jokers. Episodes between 60 and 90 minutes in length. We’ve done more than a few so far and it doesn’t seem like we’ll be stopping any time soon! Hi Loren!

  1. 3D AGO

    Episode 25: A Python That Never Was

    What if some rejected PEPs were actually accepted? How would Python look today? Let's go through 10 PEPs from the past and imagine an alternative future for the language! ## Timestamps (00:00:00) INTRO (00:01:00) PART 1: What if rejected PEPs were accepted? (00:02:15) PEP 638: Syntactic Macros (00:13:53) PEP 505: None-aware operators (00:37:12) PEP 671: Late-bound function argument defaults (00:44:40) PEP 335: Overloadable Boolean Operators (00:50:53) PEP 3136: Labeled break and continue (00:52:49) PEP 463: Exception-catching expressions (01:00:58) PEP 511: API for code transformers (01:06:30) PEP 340: Anonymous block statements (01:10:30) PEP 276 and PEP 284: Alternative integer iteration (01:17:12) The do: while: loop (01:19:50) The final boss of Python syntax feature requests (01:25:33) PART 2: PR OF THE WEEK (01:36:17) Raw f-string format fixes (01:38:44) PART 3: WHAT'S GOING ON IN CPYTHON (01:40:55) Python 3.14 RC2 and Python 3.13.7 (01:43:20) Welcome to the core team, Emma (01:43:50) Welcome to the release team, Savannah (01:45:56) Free threading changes (01:47:49) Perf improvements (01:52:00) New features (01:57:20) Bugfixes (01:59:15) OUTRO

    2h 1m

  2. JUL 12

    The Megahertz

    Python 3.14? That's old news. Let's talk about the first big feature of Python 3.15 -- a built-in sampling profiler for Linux, macOS, and Windows. We also cover improvements in perf support, discuss memory.python.org, and as usual, recent changes in the codebase. ## Timestamps (00:00:00) INTRO (00:02:43) PART 1: THE SAMPLING PROFILER (00:05:07) Built-in profile is bad, long live cProfile (00:10:54) Out-of-process profiling (00:12:18) Shortcuts Compromise Accuracy, Leading Eventually to Numerous Errors (00:16:07) Selfish Łukasz vs benevolent Pablo (00:23:11) How does a sampling profiler even work? (00:30:42) One meeellion huuurtzzz (00:32:40) Free threading makes it extra spicy (00:41:26) AsyncIO makes it even spicier (00:49:49) You made this? I made this (00:54:06) What if the profiled process changes during sampling? (00:57:33) Coming in October 2026 (01:04:30) PART 2: PR OF THE WEEEEEEK (01:14:14) memory.python.org launched (01:23:15) PART 3: WHAT'S GOING ON IN CPYTHON (01:26:45) Performance updates (01:30:24) Features & Curiosities (01:41:45) OUTRO

    1h 42m

  3. JUN 13

    PyCon US 2025 Recap

    We’ve been gone a while. Here’s our excuse for being silent for a month: PyCon, PyCon, something something security. Come listen to how the conference looked like from our perspective! And whatever you do, DO NOT upgrade to Python 3.13.4. ## Timestamps (00:00:00) INTRO (00:01:06) PART 1: LANGUAGE SUMMIT (00:04:47) A bit about the Summit talks (00:06:19) Is free-threading happening? (00:09:20) Łukasz and his favorite discussion item at the Summit (00:13:38) Find actual competent coverage of the Summit on the PSF blog (00:14:17) PART 2: PYCON TALK HIGHLIGHTS (00:14:33) Cory Doctorow's opening keynote (00:18:17) Brandt Bucher's talk on JIT challenges (00:28:28) Lysandros and Nathan talk about community adoption of free-threading (00:36:23) Lynn Root's keynote (00:37:46) PyXL: Python-oriented chip (00:39:47) Łukasz and his tutorial on WebGL with PyScript (00:47:58) A new bet appears! (00:48:14) Zoom, Enhance the Banana (00:54:11) Watch out, Łukasz is talking about audio again (01:02:42) Ivona and Pablo talk about remote code execution as a service (01:05:44) Core Python sprints after the conference (01:12:48) PART 3: PR OF THE WEEK (01:13:00) tarfile security fixes (01:19:13) Pablo's PR: strncmp considered harmful (01:25:36) PART 4: WHAT'S GOING ON IN CPYTHON (01:26:06) compression.zstd lands (01:28:01) concurrent.futures → asyncio.Future transfer 4X faster (01:29:14) Bugfix: PyCFuncPtr_call no longer uses locks (01:30:13) Some curiosities (01:34:14) OUTRO

    1h 36m

  4. MAY 6

    Beta Frenzy

    Python 3.14 Beta 1 is coming! And that means we reach feature freeze. BUT QUICK, there’s still time to squeeze in one last thing! ## Timestamps (00:00:00) INTRO (00:01:58) PART 1: Template strings (00:07:10) PART 2: Asyncio Introspection (00:29:07) PART 3: Syntax highlighting (00:43:00) PART 4: Color themes (00:50:56) PART 5: Debugging a remote process with pdb (01:01:35) PART 6: Python Installation Manager for Windows (01:05:29) PART 7: Worship (01:08:53) PART 8: What else is happening? (01:16:03) OUTRO

    1h 19m

  5. APR 17

    Episode 21: A Garbage Episode

    We talked about this episode for months now, and it's finally here. Garbage collection in its full glory. Classic and free-threaded. Generational and single-pass. With eager and delayed untracking. We cover it all! Explicitly. ## Timestamps (00:00:00) THE F*****G INTRO (00:02:03) PART 0: SPORTS NEWS (00:03:19) PART 1: GARBAGE COLLECTION (00:03:57) The big problem with refcounting (00:08:35) Solving reference cycles through PyGC_Head (00:11:45) 64 bits ought to be enough for anybody (00:17:30) Why a doubly-linked list? (00:21:15) How reference counting makes finding cycles easier (00:26:25) Roots bloody roots (00:30:17) How are objects in the cycle destroyed? (00:31:58) Object resurrection (00:43:21) Why do you need "generations"? (00:52:26) Delayed untracking (00:54:46) Weak references, strong problems (00:59:19) GC in free threading (01:03:27) Reference counting in free-threading builds (01:10:08) Incremental GC talk is DEFERRED (01:11:00) PART 2: PR OF THE WEEK (01:17:15) Type checking the standard library itself? (01:29:51) PART 3: WHAT'S GOING ON IN CPYTHON? (01:30:15) Free-threading changes (01:32:54) Performance updates (01:36:11) http.server supports HTTPS! (01:37:01) PEP 768 and 758 landed (01:37:34) HACL* (01:38:24) fnmatch.filterfalse() (01:38:54) Bugfixes (01:42:46) Curiosities (01:54:49) OUTRO

    1h 58m

  6. MAR 24

    Episode 20: Remote Code Execution By Design

    In this episode, Pablo's avoiding the topic of garbage collection by talking about his latest PEP, which allows unprecedented interaction with a running Python process. We also resolve the bet about reference counting semantics, mention some notable changes in Python since the last episode, and discuss syntax highlighting in PyREPL and why it's bad, actually. ## Timestamps (00:00:00) INTRO (00:02:16) PART 1: PABLO'S LATEST PEP (00:04:34) gdb is IMPOSSIBLE (00:12:49) Make the process run code for you (00:14:14) This already works on PyPy (00:15:13) How does it work? (00:25:38) Why a file? (00:31:15) What if you don't trust Pablo? (00:32:57) sys.remote_exec() (00:36:09) Less obvious use cases (00:46:56) PART 2: BETS (00:55:44) PART 3: PR OF THE WEEK (00:55:50) Łukasz: syntax highlighting in PyREPL (01:10:14) Pablo's PR: allow the parser to activate future imports on the fly (01:20:11) PART 4: WHAT'S GOING ON IN CPYTHON (01:20:22) Free threading (01:23:30) Performance (01:34:41) PEP 765 implemented (01:36:08) concurrent.futures.Executor.map(buffersize=) (01:36:57) io.Reader and io.Writer (01:38:40) Pabluco's linecache fetching interactive source code (01:41:25) ast.unparse() roundtrip with semicolons (01:41:59) OUTRO

    1h 44m

  7. MAR 8

    Episode 19: Async hacks, unicorns and velociraptors

    In this asynchronous episode we're interviewing a fellow core developer Yury Selivanov to talk about asyncio's past and future, composable design, immutability, and databases you'd actually like using. We also broke the 2-hour episode barrier! ## Timestamps (00:00:00) INTRO (00:01:33) PART 1: INTERVIEW (00:02:27) What drives you? (00:04:47) How do you choose what to work on? (00:08:10) Hyperfocus (00:09:28) Things from Rust that Python could use (00:14:50) Nothing is sacred when you depend on glibc (00:18:47) TypeScript typing is god-tier (00:22:04) Adding async and await to Python (00:34:11) Adding new keywords to the language (00:41:17) Jumping into a new codebase (00:49:22) Any design regrets? (00:58:46) Contextvars (01:10:40) Is the frozenmap PEP happening? (01:19:21) uvloop (01:23:25) What makes Gel lovable? (01:39:57) PART 2: PR OF THE WEEK (01:47:08) Saturday talks at PyCon should be fun (01:50:35) PART 3: WHAT'S GOING ON IN CPYTHON (01:50:47) Ken Jin's tail-call interpreter (01:55:05) Barney Gale's glob.glob() optimization (01:55:43) Brandt's boolean guards to narrow types to values in the JIT (01:56:33) Mark Shannon's stack limits implemented with addresses, not counters (01:58:34) Brandt's removal of _DYNAMIC_EXIT (01:58:53) Mark Shannon's async for branches instrumented (01:59:36) Free-threading changes (01:59:58) Sam Gross' regression tests can now run in --parallel-threads (02:00:34) Tomasz Pytel's thread safety crusade (02:01:01) Xuanteng Huang's __annotations__ race fix (02:01:11) Kumar's per-thread linked lists for tasks (02:02:54) Serhiy's crashes related to PySys_GetObject() fixed (02:03:22) Sam's usage of stack pointers in thread stack traversal (02:03:38) Dino Viehland's lock avoidance during object cleanup (02:04:23) OUTRO

    2h 7m

  8. JAN 24

    Episode 18: Reference Counting

    After we talked about memory allocation in Python back in Episode 16, we're ready to complain, uh, explain reference counting. Or at least throw a bunch of reference counting facts at you. Plus a big assortment of recent Python changes. You ready? ## Timestamps (00:00:00) INTRO (00:04:17) PART 0: SPORTS NEWS (00:06:53) PART 1: REFERENCE COUNTING (00:08:28) New segment of 2025 (00:13:54) C++ is asymptotic Python (00:15:37) Is Rust game yet? (00:18:01) Names (00:20:25) Breaking the law (00:23:08) sys.getrefcount() (00:25:21) Pedantic Pablo (00:26:06) sys.gettotalrefcount() (00:31:24) TraceRefs (00:33:28) Advantages of refcounting (00:36:16) Disadvantages of refcounting (00:38:40) Reference cycles (00:40:39) Multithreading (00:41:25) When refcounting goes wrong (00:44:05) Freeing memory in Python doesn't return it to the OS (00:45:42) Leaks and cycles redux (00:50:29) Double free (00:53:05) Avoiding reference counting (00:54:59) Immortal objects (01:00:40) PART 2: WHAT'S GOING ON IN CPYTHON (01:02:43) New features (01:04:11) Assorted interesting changes (01:15:23) Performance (01:18:09) Free-threading changes galore (01:27:02) AsyncIO (01:34:25) Windows changes (01:36:45) Security (01:37:20) OUTRO

    1h 39m
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Ratings & Reviews

5
out of 5
17 Ratings

About

We talk about Python internals, because we work on Python internals. We joke about stuff, because we’re jokers. Episodes between 60 and 90 minutes in length. We’ve done more than a few so far and it doesn’t seem like we’ll be stopping any time soon! Hi Loren!

Information

  • Creator
    Pablo Galindo and Łukasz Langa
  • Years Active
    2023 - 2025
  • Episodes
    25
  • Rating
    Explicit
  • Copyright
    © Pablo Galindo and Łukasz Langa
  • Show Website
    core.py

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