RuntimeWarning: Sequential read of iterator was interrupted. Resetting iterator. This can negatively impact the performance.

The RuntimeWarning does not appear in 1.8.17. I think this is a regression introduced in 1.8.18. Related SO question: https://stackoverflow.com/q/64995369/9778755

_Originally posted by @StefanBrand in https://github.com/Toblerity/Fiona/issues/965#issuecomment-737073718_

[rbuffat]

So what’s going on is that the list() method seems to call len() before it starts iterating over the Iterator. I assume this is to create an efficient data structure for the list. Would be interesting to look at the implementation of list(). We probably should not emit a warning when the iterator was interrupted before an iteration has actually started.

class Iterator:

    def __init__(self):
        print("__init__")
        self.counter = 0
        self.len = 5

    def __iter__(self):
        print("__iter__")
        return self

    def __next__(self):
        self.counter += 1
        if self.counter > self.len:
            raise StopIteration
        print("__next__", self.counter)
        return self.counter

    def __len__(self):
        print("__len__")
        return self.len

it = Iterator()
print(list(it))

Output:

__init__
__len__
__iter__
__len__
__next__ 1
__next__ 2
__next__ 3
__next__ 4
__next__ 5

[Robinlovelace]

Thanks for the explanation @rbuffat, sounds reasonable. Checking here it seems that there are indeed later versions available: https://anaconda.org/conda-forge/fiona

I’m guess it may be because we pin the Python version as follows:

name: geocompy
channels:
  - conda-forge
  - default
dependencies:
  - python=3.9

Plan to set that as

  - python>=3.9

Source: https://github.com/geocompr/py/blob/main/environment.yml