Python wrapper API has changed; python examples are not working

[jake-low]

The python examples in the repository aren't working. As an example, here's me running read_way.py.

$ python python/examples/read_way.py washington.osmx 761811137
Traceback (most recent call last):
  File "/Users/jake/Code/FOSS/protomaps/OSMExpress/python/examples/read_way.py", line 18, in <module>
    for node_id in way.nodes:
                   ^^^^^^^^^
AttributeError: '_GeneratorContextManager' object has no attribute 'nodes'

The augmented_diff.py script fails similarly:

python python/examples/augmented_diff.py washington.osmx 155421965.osc 155421965.adiff
No old loc found for tagless node 5694096597
Traceback (most recent call last):
  File "/Users/jake/Code/FOSS/protomaps/OSMExpress/python/examples/augmented_diff.py", line 138, in <module>
    set_old_metadata(prev_version)
  File "/Users/jake/Code/FOSS/protomaps/OSMExpress/python/examples/augmented_diff.py", line 74, in set_old_metadata
    elem.set('version',str(o.metadata.version))
                           ^^^^^^^^^^
AttributeError: '_GeneratorContextManager' object has no attribute 'metadata'

The root cause is that pycapnp from_bytes() now returns a context manager, requiring callers to change from this:

way = messages_capnp.Way.from_bytes(msg)
# do stuff with way

...to this:

with messages_capnp.Way.from_bytes(msg) as way:
    # do stuff with way

This change was introduced in pycapnp 1.1.1. It looks like the Python examples were developed against an older version of OSMX that used pycapnp 0.6.4, but #46 bumped the pycapnp version to 2.0.0. This effectively changed the API of nodes.get(), ways.get(), etc by making them return context managers rather than return nodes/ways/etc directly, but I assume this wasn't noticed at the time and the examples weren't updated to match.

I think there are two possible fixes: either downgrade the Python osmx wrapper to use pycapnp <= 1.1.0, or change the Python examples to use with. I'm not sure which is more appropriate. It's worth noting that if pycapnp ~= 2.0.0 is kept, the next release of osmx will be a breaking API change for any users of the Python wrapper.

EDIT: Actually it looks like a version with the new context-manager API has already been published, though as a 0.0.x release I think most users would know not to expect a stable API 😉

I might be able to work on a PR for this at some point soon, but wanted to open this issue for now in case I don't end up having time to.

[bdon]

maybe it was this that wasn't merged yet: https://github.com/protomaps/OSMExpress/commits/python-api-enhancements/