Libptr by env (#781)

* pass libptr by env var instead

* update changelog

---------

Co-authored-by: Christopher Rowley <github.com/cjdoris>

Author: cjdoris

CHANGELOG.md

@@ -1,8 +1,9 @@
 # Changelog
 
 ## Unreleased
-* Add method `pynext(x, d)` to return a default value `d` if there are no more elements.
 * Add option `lib` to JuliaCall. Setting this will skip the discovery subprocess.
+* Add support for using a system image in `juliacall` that has `PythonCall` baked in.
+* Add method `pynext(x, d)` to return a default value `d` if there are no more elements.
 * Bug fixes.
 
 ## 0.9.34 (2026-05-18)

pysrc/juliacall/__init__.py

@@ -242,6 +242,11 @@ def args_from_config(config):
     jl_parse_opts(c.pointer(argc), c.pointer(argv))
     assert argc.value == 0
 
+    # override some environment variables
+    # we do this here because PythonCall is initialised during jl_init if it is in a sysimg
+    os.environ['JULIA_PYTHONCALL_EXECUTABLE'] = sys.executable or ''
+    os.environ['__JULIA_PYTHONCALL_EMBEDDED_LIBPTR__'] = hex(c.pythonapi._handle)
+
     # initialise julia
     try:
         jl_init = lib.jl_init_with_image__threading
@@ -271,23 +276,22 @@ def jlstr(x):
         return 'raw"' + x + '"'
     script = '''
     try
-        Base.require(Main, :CompilerSupportLibraries_jll)
-        global __PythonCall_libptr = Ptr{{Cvoid}}(UInt({}))
-        ENV["JULIA_PYTHONCALL_EXE"] = {}
+        import CompilerSupportLibraries_jll as _
         using PythonCall
     catch err
         print(stderr, "ERROR: ")
         showerror(stderr, err, catch_backtrace())
         flush(stderr)
         rethrow()
     end
-    '''.format(
-        hex(c.pythonapi._handle),
-        jlstr(sys.executable or ''),
-    )
+    '''
     res = jl_eval(script.encode('utf8'))
     if res is None:
         raise Exception('PythonCall.jl did not start properly')
+    
+    # unset this env var so any other julia processes started do not think they are
+    # embedded in python
+    os.environ.pop('__JULIA_PYTHONCALL_EMBEDDED_LIBPTR__', None)
 
     CONFIG['inited'] = True
 

src/C/context.jl

@@ -105,11 +105,14 @@ on_main_thread
 
 function init_context()
 
-    CTX.is_embedded = hasproperty(Base.Main, :__PythonCall_libptr)
+    CTX.is_embedded = haskey(ENV, "__JULIA_PYTHONCALL_EMBEDDED_LIBPTR__")
 
     if CTX.is_embedded
         # In this case, getting a handle to libpython is easy
-        CTX.lib_ptr = Base.Main.__PythonCall_libptr::Ptr{Cvoid}
+        CTX.lib_ptr = Ptr{Cvoid}(parse(UInt, ENV["__JULIA_PYTHONCALL_EMBEDDED_LIBPTR__"]))
+        # Delete the env var so subprocesses don't think they are embedded
+        delete!(ENV, "__JULIA_PYTHONCALL_EMBEDDED_LIBPTR__")
+        # Initialise pointers from libpython
         init_pointers()
         # Check Python is initialized
         Py_IsInitialized() == 0 && error("Python is not already initialized.")