🌐 Mailman 3 September 2024 - Tutor - python.org

Type hint question
by Albert-Jan Roskam Sept. 26, 2024

Sept. 26, 2024

Hi, I just started using type hints and mypy so this is probably a basic question. Why doesn't like mypy the code below? Also, I noticed that mypy seems to favour LBYL (if isinstance) to EAFP (try-except), in the sense that doesn't understand the latter well. Is this true? I'm still learning to use mypy, but sometimes it feels a lot like "pleasing mypy". Then again, it has already helped me find some errors. from typing import TypeVar T = TypeVar("T") def try_int(value: T) -> T: try: return int(value.strip(" ")) except (TypeError, AttributeError, ValueError): return value n = try_int(" 1") I get this message: main.py:7: error: Incompatible return value type (got "int", expected "T") [return-value] main.py:7: error: "T" has no attribute "strip" [attr-defined] Found 2 errors in 1 file (checked 1 source file) Thanks! Albert-Jan

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How to stop a specific thread in Python 2.7?
by marc nicole Sept. 26, 2024

Sept. 26, 2024

Hello guys, I want to know how to kill a specific running thread (say by its id) for now I run and kill a thread like the following: # start thread thread1 = threading.Thread(target= self.some_func(), args=( ...,), ) thread1.start() # kill the thread event_thread1 = threading.Event() event_thread1.set() I know that set() will kill all running threads, but if there was thread2 as well and I want to kill only thread1? Thanks!

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Clarification on .format() Method and Negative Indices in Python
by Xingyuan Shi Sept. 26, 2024

Sept. 26, 2024

Dear Python Tutor Team, I hope you are having a great day. I have been learning more about Python’s string formatting, and I came across an interesting issue regarding the .format() method. Specifically, I was curious as to why negative indices like {-1} are not supported in this method, while negative indexing works perfectly with lists and other sequences in Python. For instance, I attempted to use the following code: print("{-1},{-1},{-1}".format(20, "example", 3.14)) I expected the placeholders {-1} to behave similarly to negative indices in lists, but it resulted in an error. I understand that .format() relies on positional arguments, but I wonder if there was a specific design rationale behind not allowing negative indices here. Could you shed some light on this design choice? Thank you very much for your time and for developing such an incredible language that I thoroughly enjoy learning. Best regards, Stone

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Side effect and return value
by Albert-Jan Roskam Sept. 21, 2024

Sept. 21, 2024

Hi, I've just read "Code that fits into your Brain". The author says a function with a side effect should not have a return value. But how would one write this function in order to do that? This looks totally fine to me: from uuid import UUID from requests import post def create_user(info: dict) -> UUID: resp = post("https://some-thing/user", json=info) resp.raise_for_status() return UUID(resp.json()["id"]) Thanks! AJ

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Getting a Process.start() error pickle.PicklingError: Can't pickle <type 'module'>: it's not found as __builtin__.module with Python 2.7
by marc nicole Sept. 4, 2024

Sept. 4, 2024

Hello, I am using Python 2.7 on Windows 10 and I want to launch a process independently of the rest of the code so that the execution continues while the started process proceeds. I am using Process().start() from Python 2.7 as follows: from multiprocessing import Process def do_something(text): print(text) if __name__ == "__main__": q = Process(target=do_something,args=("somecmd") ) q.start() # following code should execute right after the q.start() call (not until it returns) ..... But getting the error at the call of Process().start(): pickle.PicklingError: Can't pickle <type 'module'>: it's not found as __builtin__.module anybody could provide an alternative to call the function do_something() in a separate thread ?

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