Re: "undefined behavior"?

On 15/06/2024 06:45, DFS wrote:

On 6/14/2024 11:56 PM, Keith Thompson wrote:

DFS <nospam@dfs.com> writes:

On 6/14/2024 9:39 PM, Keith Thompson wrote:

DFS <nospam@dfs.com> writes:
[...]

During conversion, I got a Python error I don't remember seeing in the past:
>
"TypeError: list indices must be integers or slices, not float"
>
because division returns a float, and some of the array addressing was
like this: nums[i/2].

[...]
C's "/" operator yields a result with the type of the operands
(after
promotion to a common type).
Python's "/" operator yields a floating-point result.  For C-style
integer division, Python uses "//".  (Python 2 is more C-like.)

>
I was surprised python did that, since every division used in the
array addressing results in an integer.
>
After casting i to an int before any array addressing, // works.

>
I'm surprised you needed to convert i to an int.  I would think that

 > just replacing nums[i/2] by nums[i//2] would do the trick,
 > as long> as i always has an int value (note Python's dynamic typing).   If i

is acquiring a float value, that's probably a bug, given the name.

 I spotted the issue.  Just prior to using i for array addressing I said:
i = N/2.
 The fix is set i = int(N/2)
  

But if you want help with your Python code, comp.lang.python is the
place to ask.

 Thanks for your help, but David Brown is a Python developer and I'll ask him python questions here whenever I care to.
 

I consider myself more of a C developer than a Python developer, but I use Python regularly.  I would say that my knowledge of the C language and standard, while not as deep as some others here, covers a far higher proportion of the language than my knowledge of Python covers of Python.   But I think you can make good use of Python while knowing a smaller fraction of the language and library than for C.

In the recent past you were involved in discussions on perl, Fortran and awk, among other off-topics.
 Rules for thee but not for me?
 

If occasional questions or discussions about other languages pop up here, people will often answer them.  But for more in-depth discussions or questions, this is not the newsgroup - comp.lang.python is the place for Python questions.  (You'll also probably get better answers there than I can give.)
The rules are for everyone, but they are a bit fuzzy.  (And different posters have different levels of fuzziness.)