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--- python [2025/05/08 10:51] – created carl
+++ python [2026/01/12 10:13] (current) – carl
@@ Line 8: / Line 8: @@
-  * Typesafety is complex.  Static checkers are okay, but the runtime type system is pretty weak.  There is no equivalent of type capture in Java (e.g. ''static <T> List<T> makeList(T item) {...}''
+==== Typesafety is complex. ====
+Static checkers are okay, but the runtime type system is pretty weak.  There is no equivalent of type capture in Java (e.g. ''static <T> List<T> makeList(T item) {...}''
+==== ''isinstance()'' ====
+[[https://www.reddit.com/r/learnpython/comments/1dz56ep/isinstancex_listlistint_doesnt_work/|throws]] if the second arg is a generic type.  For example ''isinstance(var, dict[str, Any])''.   This is annoying because you only find out at runtime that it's broken.
+==== Lack of Queue implementations ====
+Trying to implement Java's ThreadPoolExecutor needs more diverse Queue implementations.
+  * ''queue.Queue'' throws exceptions when the queue is empty, rather than returning None
+  * ''queue.Queue'' calls can't be interrupted.
+  * No way to have a handoff, similar to ''SynchronousQueue'' in Java.  This class is the key to a cached [[java:threadpoolexecutor|ThreadPoolExecutor]].
+  * ''queue.SimpleQueue'' timeout doesn't work.  The task-tracking part of Queue and the timeout handling come as a package deal, meaning you get both or neither.
+==== Problems with Multiprocessing ====
+Caching comes in many forms, but one surprising way that it shows up is in connection caching (a.k.a. pooling).  Without special handling, connections cannot be shared between processes.   When a Python program spawns another process, the new process does not inherit the file descriptors (fds) and thus has to re create them itself.  This has many problems:
+  * For socket fds, reconnecting is slow. for the caller
+  * For socket fds, re-establing an SSL connection is very slow and CPU intensive
+  * For socket fds, reconnecting causes the remote endpoint to burn resources as well.
+  * For file fds, its not possible to synchronize access to them.  (if Python had better shared memory support and the correct atomics to modify the memory, this may be possible).
+Multiprocessing skips the ''atexit'' hooks, meaning it's not possible to do process-wide cleanup work.  They are silently skipped.
+==== Problems with Descriptors ====
+Evaluation order matters.  For example:
+<code python>
+a: Descriptor
+b: Descriptor
+foo(a, b)
+</code>
+In this, if a or b have side-effects on evaluation, like throwing an exception, the order in which a and b are invoked matters.
+==== Futures ====
+  * Futures don't have a getstate() method.  This means trying to find out the running/finished/cancel/pending states of a future are racy.   The lock (condition) on the future is also private, so it's not safe to lock and query each of the state methods.