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What resources did YOU use to learn Python?
Hello! I am new to python. I created a script/bot, and its function is work until closed.
That bot has a main() function that one way or another calls itself after a 1 minute timer.
After some time i noticed that it crashed and closed Tested again but now in Visual Studio Code and after 18 hours it crashed again with fatal error stack overflow.
Went in and created a separate script with a main function calling itself and after 1035 loops it caused stack overflow. Now 1035*1minute is about 18 hours.
How can i create an infinite script without causing stack overflow?
Thanks!
Just wondering what books/resource you use/used to learn Python. Excluding the Documentation, Codecademy, and LPTHW
You can cause a stack overflow quite easily in python, as in any other language, by building an infinately recursive funcion. This is easier in python as it doesn't actually have to do anything at all other than be recursive.
>>> def foo():
... return foo()
...
>>> foo()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
.......
File "<stdin>", line 2, in foo
RuntimeError: maximum recursion depth exceeded
>>>
As for the heap, that is managed by a garbage collector. You can allocate lots of objects and eventually run out of heap space and Python will raise a MemoryError, but it's going to take a fair amount of time. You actually did that with your 'stack overflow' example in the question. You stored a reference to a string on the stack, this string took up all the free memory available to the process. As a rule of thumb, Python stores a reference to a heap structure on the stack for any value that it can't guarantee the size of.
As for how it all works, from the fist example you can see that python has a built-in limit to the depth of the call stack that it will not exceed. The amount of memory available for heap space is defined by the OS however and will depend upon many factors.
These are should be the appropriate parts of the python docs for infomation on the errors themselves:
- http://docs.python.org/release/3.2.3/library/exceptions.html#RuntimeError
- http://docs.python.org/release/3.2.3/library/exceptions.html#MemoryError
please correct me if wrong:
As far as I know, when it comes to actual stack implementation, the python stack (in the default distribution) is actually based in the heap memory (memory allocated with malloc). So you cannot cause the stack overflow, but you can run out of memory. The computer slowdown you seen is because memory is being swapped to disk, very slow procedure.
generally, you have no idea how the interpreted/byte-compiled language implements its stack, but most like it is not implemented in the stack memory, so you cannot cause stack overflow. it is possible to implement Python using alloca, but why?
Cf. CPython - Internally, what is stored on the stack and heap?
Try the same experiment with compiled language, C++, Fortran, etc. which compiles to machine code.
If you need to learn python from scratch - you can start here: http://docs.python.org/tut/tut.html - good begginers guide
If you need to extend your knowledge - continue here http://diveintopython3.ep.io/ - good intermediate level book
If you need perfect skills - complete this http://www.pythonchallenge.com/ - outstanding and interesting challenge
And the perfect source of knowledge is http://docs.python.org/ - collection of all knowledge
If you're a beginner, try my book A Byte of Python.
If you're already experienced in programming, try Dive Into Python.