Hello, Am 25.07.20 um 23:45 schrieb Philipp Hahn:
Am 27.04.20 um 15:44 schrieb Philipp Hahn:
I'm working on adding PEP 484 type hints <https://www.python.org/dev/peps/pep-0484/> to the Python binding of libvirt. ... I just opened a merge request <https://gitlab.com/libvirt/libvirt-python/-/merge_requests/9> for my code at <https://gitlab.com/pmhahn/libvirt-python/-/tree/typing>.
While working on that I stumbled over some annoyances in the current Python API: There are many methods which return a List[int], for example: virDomainGetInfo virDomainGetState virDomainGetControlInfo virDomainGetBlockInfo virDomainGetJobInfo virStoragePoolGetInfo virStorageVolGetInfo virStorageVolGetInfoFlags There are more function returning similar information as plain List: virNodeGetSecurityModel virNodeGetSecurityModel virDomainGetSecurityLabelList virDomainBlockStats virDomainInterfaceStats virDomainGetVcpus virNodeGetCPUMap The worst offender is `virNodeGetInfo`, which returns `Tuple[str, int*7]`: The problem for type annotation is that `List` is unlimited in the number of elements, that is you cannot specify the number of entries the list must or will contain. Also all elements of a list must have the same (super-)type; for "str" and "int" of "virNodeGetInfo()" that would be "Any", which is not very useful here. A better type for those `List`s would be `Tuple`, which has a fixed length and can have different types for each position. But that would be an API change: In most cases users of those functions should not notice the difference as indexing tuples or lists is the same. It would break code where someone would do something like this: ret = virFunction_returning_list() ret += [1, 2, 3] which breaks if that function would return a `Tuple` in the future:
$ python -c '() + []' Traceback (most recent call last): File "<string>", line 1, in <module> TypeError: can only concatenate tuple (not "list") to tuple
Even better then plain `Tuple`s would be <https://docs.python.org/3/library/collections.html#collections.namedtuple>, which would allow us to use the return value of `virNodeGetInfo()` as this:
from collections import namedtuple import libvirt virNodeInfo = namedtuple("virNodeInfo", ["model", "memory", "cpus", "mhz", "nodes", "sockets", "cores", "threads"]) c = libvirt.open('test:///default') info = virNodeInfo(*c.getInfo()) print(info.model) print(info) # virNodeInfo(model='i686', memory=3072, cpus=16, mhz=1400, nodes=2, sockets=2, cores=2, threads=2)
<https://libvirt.org/html/libvirt-libvirt-host.html#virNodeInfo> This could be improved even more by using <https://mypy.readthedocs.io/en/stable/kinds_of_types.html?highlight=NamedTuple#named-tuples>, which allows to add type information:
from typing import NamedTuple virNodeInfo = NamedTuple("virNodeInfo", [("model", str), ("memory", int), ("cpus", int), ("mhz", int), ("nodes", int), ("sockets", int), ("cores", int), ("threads", int)])
or with Python 3.6 the more readable form
class virNodeInfo(NamedTuple): model: str memory: int cpus: int mhz: int nodes: int sockets: int cores: int threads: int
IMHO that would be a real usability improvement as I have to lookup that information every time I have to use those functions myself. Indexing with `namedtuple` and `NamedTuple` still works, so you can still use `info[0]` above to get the model. What do you think of that? When would be a good time to make such a change? Philipp