3 ms·

You can create a file, example.py: import time value = "foo" def go(): for i in range(10): print("...", i, value) time.sleep(

by ks2048 2y ago

You can create a file, example.py: import time value = "foo" def go(): for i in range(10): print("...", i, value) time.sleep(3) Then, in repl, import example import threading thread = threading.Thread(target=example.go) thread.start() It will slowly print out messages and you can do "example.value = 'bar'" in the REPL and it will change.

behnamoh 2y ago
it's not the same though—In Lisp, when you compile your program, a Lisp run-time is attached to it so you can either run the program normally (like any binary) or you could REPL into the program and see what the values of variables are (these values were set at compile time). This is helpful when you have a large dataset you don't want to load over and over.
- zahlman 2y ago
  Have you tried out the Python standard library debugger (pdb)?
- d0mine 2y ago
  Repl can be attached to a live python process (you don't need to restart anything) https://stackoverflow.com/questions/1395913/how-to-drop-into-repl-read-eval-print-loop-from-python-code https://stackoverflow.com/questions/1395913/how-to-drop-into... You could do it even without cooperation from the python app using approach similar to pyrasite (though it is much easier with cooperation--just add a couple of lines).
  - behnamoh 2y ago
    That only works where you specified (e.g., line 42 where you invoke `code.interact(local=locals()`). Lisp's approach works anywhere (anytime an exception is raised you're thrown in the REPL).
    - d0mine 2y ago
      gc allows to get any [non-leaky] object from anywhere. You can even drop into repl over the network. Debugger can be started on exception if desired e.g., pytest provides `--pdb` arg. Though repl is different--you don't need to interrupt the app itself while you are inspecting it e.g., async repl can be run in the same thread alongside the rest of the app. I can't remember a single case there Python's dynamism weren't enough for the task (most of the times it is the opposite--there could be less dynamism).
Y_Y 2y ago
That's a nice trick! For reference, what I'd normally do if I wanted that is specify launching with the debugger, like python3 -mpdb example.py and then step through. Also `ipdb` is nice if available.
handman 2y ago
This is nothing like the Lisp debugger. It is very hard to convince Pythonistas of the fact: https://news.ycombinator.com/item?id=36888648 https://news.ycombinator.com/item?id=36888648
- ks2048 2y ago
  Interesting thread. I only read some of it, but I did find one answer that tells me how Python and LISP differ: As an example, I suppose that when you’re developing code in Python’s pseudo-REPL you often reimport a file containing class definitions. When you do that, what happens to all the old objects with the old class definition? Nothing, they still belong to the old class. ... In Lisp, it’s different. There is a defined protocol for what happens when a class is redefined. Every single object belonging to the old class gets updated to the new class.
  - behnamoh 2y ago
    > In Lisp, it’s different. There is a defined protocol for what happens when a class is redefined. Every single object belonging to the old class gets updated to the new class. This. Lisp gives you ultimate power but of course, it means it unlocks more ways to shoot yourself in the foot in the process. Most organizations don't want "smart hacky" solution (i.e., they don't want you as the programmer to fix issues in creative ways that Lisp provides to you), instead, they want "standard processes" that can be taught to new hires (i.e., they want you as the programmer to write standard, idiomatic code that everyone understands). The latter comes at the cost of less flexibility (i.e., when your rock solid code crashes, it means you must update the source code instead of fixing it on the go like in Lisp restarts).
  - kazinator 2y ago
    This protocol is in Common Lisp. Common Lisp is not Lisp. Not every Lisp has CLOS. Common Lisp is not the be-all end-all in Lisp. Redefining the classes of objects at run-time is not unilaterally a great idea. It's not obvious how to implement it in such a way that applications which don't use it don't have to pay any extra cost for the support. There being a defined protocol for what happens when a class being redefined does not add up to you automatically having an application that can upgrade itself while it is running, from any version to any version, bug free. You have to test and debug all the combinations, or else support only certain combinations, requiring multiple upgrades. This is something that will add complexity to your upgrade plan. I can see someone like NASA using such a tool for a very specific scenario, which can be replicated on Earth and tested, and then carried out remotely in some space probing vessel.

by ks2048 2y ago

behnamoh 2y ago

it's not the same though—In Lisp, when you compile your program, a Lisp run-time is attached to it so you can either run the program normally (like any binary) or you could REPL into the program and see what the values of variables are (these values were set at compile time). This is helpful when you have a large dataset you don't want to load over and over.

zahlman 2y ago
Have you tried out the Python standard library debugger (pdb)?
d0mine 2y ago
Repl can be attached to a live python process (you don't need to restart anything) https://stackoverflow.com/questions/1395913/how-to-drop-into-repl-read-eval-print-loop-from-python-code https://stackoverflow.com/questions/1395913/how-to-drop-into... You could do it even without cooperation from the python app using approach similar to pyrasite (though it is much easier with cooperation--just add a couple of lines).
- behnamoh 2y ago
  That only works where you specified (e.g., line 42 where you invoke `code.interact(local=locals()`). Lisp's approach works anywhere (anytime an exception is raised you're thrown in the REPL).
  - d0mine 2y ago
    gc allows to get any [non-leaky] object from anywhere. You can even drop into repl over the network. Debugger can be started on exception if desired e.g., pytest provides `--pdb` arg. Though repl is different--you don't need to interrupt the app itself while you are inspecting it e.g., async repl can be run in the same thread alongside the rest of the app. I can't remember a single case there Python's dynamism weren't enough for the task (most of the times it is the opposite--there could be less dynamism).

Y_Y 2y ago

That's a nice trick! For reference, what I'd normally do if I wanted that is specify launching with the debugger, like python3 -mpdb example.py and then step through. Also `ipdb` is nice if available.

handman 2y ago

This is nothing like the Lisp debugger. It is very hard to convince Pythonistas of the fact: https://news.ycombinator.com/item?id=36888648 https://news.ycombinator.com/item?id=36888648

ks2048 2y ago
Interesting thread. I only read some of it, but I did find one answer that tells me how Python and LISP differ: As an example, I suppose that when you’re developing code in Python’s pseudo-REPL you often reimport a file containing class definitions. When you do that, what happens to all the old objects with the old class definition? Nothing, they still belong to the old class. ... In Lisp, it’s different. There is a defined protocol for what happens when a class is redefined. Every single object belonging to the old class gets updated to the new class.
- behnamoh 2y ago
  > In Lisp, it’s different. There is a defined protocol for what happens when a class is redefined. Every single object belonging to the old class gets updated to the new class. This. Lisp gives you ultimate power but of course, it means it unlocks more ways to shoot yourself in the foot in the process. Most organizations don't want "smart hacky" solution (i.e., they don't want you as the programmer to fix issues in creative ways that Lisp provides to you), instead, they want "standard processes" that can be taught to new hires (i.e., they want you as the programmer to write standard, idiomatic code that everyone understands). The latter comes at the cost of less flexibility (i.e., when your rock solid code crashes, it means you must update the source code instead of fixing it on the go like in Lisp restarts).
- kazinator 2y ago
  This protocol is in Common Lisp. Common Lisp is not Lisp. Not every Lisp has CLOS. Common Lisp is not the be-all end-all in Lisp. Redefining the classes of objects at run-time is not unilaterally a great idea. It's not obvious how to implement it in such a way that applications which don't use it don't have to pay any extra cost for the support. There being a defined protocol for what happens when a class being redefined does not add up to you automatically having an application that can upgrade itself while it is running, from any version to any version, bug free. You have to test and debug all the combinations, or else support only certain combinations, requiring multiple upgrades. This is something that will add complexity to your upgrade plan. I can see someone like NASA using such a tool for a very specific scenario, which can be replicated on Earth and tested, and then carried out remotely in some space probing vessel.