A proc that returns a string seems to be seen as a int in python

[JohnAD]

I've been impressed by this library. It seems to greatly simplify the interface between nim and python.

Unfortunately, I've been having problems with def procs that return strings.

So, to provide a simplified example, a bindings.nim:

import unicode

import genny

import txtdb

proc joe(): string =
    result = "hello"

exportProcs:
  joe

writeFiles("bindings/generated", "txtdb")
include generated/internal

Examining the internal file:

proc txtdb_joe*(): cstring {.raises: [], cdecl, exportc, dynlib.} =
  joe().cstring

And yet, if I call it from python:

test = dll.txtdb_joe().decode("utf8")

I get:

Traceback (most recent call last):
  File "/home/johnd/Projects/pytxtdb/tests/test_load.py", line 16, in <module>
    result = person_table.create(person_c)
  File "/home/johnd/Projects/pytxtdb/src/txtdb.py", line 40, in create
    test = dll.txtdb_joe().decode("utf8")
AttributeError: 'int' object has no attribute 'decode'

Details:

Running on Pop_OS!, an ubuntu variant. So, using libtxtdb.so. Nim is version 1.4.8. Python is

Python 3.9.5 (default, May 11 2021, 08:20:37) 
[GCC 10.3.0] on linux

genny version is genny [0.1.0]

Thanks for any help you can provide!

[guzba]

Interesting issue. Thanks very much for trying genny and for reporting this issue along with great information so we can reproduce it. Will reply back here with an update soon.

[guzba]

Ok this took a bit longer than I expected to get back to but I do have an update. I am not able to reproduce the issue, but I do know we haven't really documented well how to set things up so there could be many issues along the way. Some things:

nim c -f -d:release --app:lib --gc:arc --tlsEmulation:off --out:txtdb bindings.nim or something like this should be the compile command.

From here, the generated python file does need a tweak to work without the pip set up (which is too much for a simple test). An modified output python file would be:

from ctypes import *
import os, sys

dir = os.path.dirname(os.path.abspath(__file__))
if sys.platform == "win32":
  libName = "txtdb.dll"
elif sys.platform == "darwin":
  libName = "libtxtdb.dylib"
else:
  libName = "libtxtdb.so"
dll = cdll.LoadLibrary(os.path.join(dir, libName))

class txtdbError(Exception):
    pass

def joe():
    result = dll.txtdb_joe().decode("utf8")
    return result

dll.txtdb_joe.argtypes = []
dll.txtdb_joe.restype = c_char_p

test = joe()

print(test)

Notice that I added the print at the bottom, call joe() instead of the dll proc, and changed the dir = at the top to work with file paths. It expects the dll / so to be in the same directory as the python file, and the same directory you are running the python script.

For me, then python txtdb.py prints hello as expected.

I hope this helps and thanks for giving genny a try. As you've noticed, it is pretty cool but also quite new and rough. We'll work through it though as we put more time in on genny.

[guzba]

Closing this just for housekeeping. Please re-open if there is an update.