Add global flag

Author: pablogsal

Include/cpython/initconfig.h

@@ -190,6 +190,7 @@ typedef struct PyConfig {
     int enable_gil;
     int tlbc_enabled;
 #endif
+    int lazy_imports;
 
     /* --- Path configuration inputs ------------ */
     int pathconfig_warnings;

Python/initconfig.c

@@ -111,6 +111,7 @@ static const PyConfigSpec PYCONFIG_SPEC[] = {
     SPEC(base_prefix, WSTR_OPT, PUBLIC, SYS_ATTR("base_prefix")),
     SPEC(bytes_warning, UINT, PUBLIC, SYS_FLAG(9)),
     SPEC(cpu_count, INT, PUBLIC, NO_SYS),
+    SPEC(lazy_imports, INT, PUBLIC, NO_SYS),
     SPEC(exec_prefix, WSTR_OPT, PUBLIC, SYS_ATTR("exec_prefix")),
     SPEC(executable, WSTR_OPT, PUBLIC, SYS_ATTR("executable")),
     SPEC(inspect, BOOL, PUBLIC, SYS_FLAG(1)),
@@ -317,6 +318,8 @@ The following implementation-specific options are available:\n\
 "\
 -X importtime[=2]: show how long each import takes; use -X importtime=2 to\n\
          log imports of already-loaded modules; also PYTHONPROFILEIMPORTTIME\n\
+-X lazy_imports=[on|off|default]: control global lazy imports; default is auto;\n\
+         also PYTHON_LAZY_IMPORTS\n\
 -X int_max_str_digits=N: limit the size of int<->str conversions;\n\
          0 disables the limit; also PYTHONINTMAXSTRDIGITS\n\
 -X no_debug_ranges: don't include extra location information in code objects;\n\
@@ -431,6 +434,7 @@ static const char usage_envvars[] =
 "PYTHON_PRESITE: import this module before site (-X presite)\n"
 #endif
 "PYTHONPROFILEIMPORTTIME: show how long each import takes (-X importtime)\n"
+"PYTHON_LAZY_IMPORTS: control global lazy imports (-X lazy_imports)\n"
 "PYTHONPYCACHEPREFIX: root directory for bytecode cache (pyc) files\n"
 "                  (-X pycache_prefix)\n"
 "PYTHONSAFEPATH  : don't prepend a potentially unsafe path to sys.path.\n"
@@ -939,6 +943,8 @@ config_check_consistency(const PyConfig *config)
     assert(config->int_max_str_digits >= 0);
     // cpu_count can be -1 if the user doesn't override it.
     assert(config->cpu_count != 0);
+    // lazy_imports can be -1 (default), 0 (off), or 1 (on).
+    assert(config->lazy_imports >= -1 && config->lazy_imports <= 1);
     // config->use_frozen_modules is initialized later
     // by _PyConfig_InitImportConfig().
     assert(config->thread_inherit_context >= 0);
@@ -1050,6 +1056,7 @@ _PyConfig_InitCompatConfig(PyConfig *config)
     config->_is_python_build = 0;
     config->code_debug_ranges = 1;
     config->cpu_count = -1;
+    config->lazy_imports = -1;
 #ifdef Py_GIL_DISABLED
     config->thread_inherit_context = 1;
     config->context_aware_warnings = 1;
@@ -2284,6 +2291,49 @@ config_init_import_time(PyConfig *config)
     return _PyStatus_OK();
 }
 
+static PyStatus
+config_init_lazy_imports(PyConfig *config)
+{
+    int lazy_imports = -1;
+
+    const char *env = config_get_env(config, "PYTHON_LAZY_IMPORTS");
+    if (env) {
+        if (strcmp(env, "on") == 0) {
+            lazy_imports = 1;
+        }
+        else if (strcmp(env, "off") == 0) {
+            lazy_imports = 0;
+        }
+        else if (strcmp(env, "default") == 0) {
+            lazy_imports = -1;
+        }
+        else {
+            return _PyStatus_ERR("PYTHON_LAZY_IMPORTS: invalid value; "
+                                 "expected 'on', 'off', or 'default'");
+        }
+        config->lazy_imports = lazy_imports;
+    }
+
+    const wchar_t *x_value = config_get_xoption_value(config, L"lazy_imports");
+    if (x_value) {
+        if (wcscmp(x_value, L"on") == 0) {
+            lazy_imports = 1;
+        }
+        else if (wcscmp(x_value, L"off") == 0) {
+            lazy_imports = 0;
+        }
+        else if (wcscmp(x_value, L"default") == 0) {
+            lazy_imports = -1;
+        }
+        else {
+            return _PyStatus_ERR("-X lazy_imports: invalid value; "
+                                 "expected 'on', 'off', or 'default'");
+        }
+        config->lazy_imports = lazy_imports;
+    }
+    return _PyStatus_OK();
+}
+
 static PyStatus
 config_read_complex_options(PyConfig *config)
 {
@@ -2307,6 +2357,13 @@ config_read_complex_options(PyConfig *config)
         }
     }
 
+    if (config->lazy_imports < 0) {
+        status = config_init_lazy_imports(config);
+        if (_PyStatus_EXCEPTION(status)) {
+            return status;
+        }
+    }
+
     if (config->tracemalloc < 0) {
         status = config_init_tracemalloc(config);
         if (_PyStatus_EXCEPTION(status)) {
@@ -2696,6 +2753,9 @@ config_read(PyConfig *config, int compute_path_config)
     if (config->tracemalloc < 0) {
         config->tracemalloc = 0;
     }
+    if (config->lazy_imports < 0) {
+        config->lazy_imports = -1;  // Default is auto/unset
+    }
     if (config->perf_profiling < 0) {
         config->perf_profiling = 0;
     }

Python/pylifecycle.c

@@ -1316,6 +1316,21 @@ init_interp_main(PyThreadState *tstate)
         }
     }
 
+    // Initialize lazy imports based on configuration
+    // Do this after site module is imported to avoid circular imports during startup
+    if (config->lazy_imports != -1) {
+        PyImport_LazyImportsMode lazy_mode;
+        if (config->lazy_imports == 1) {
+            lazy_mode = PyLazyImportsMode_ForcedOn;
+        } else {
+            lazy_mode = PyLazyImportsMode_ForcedOff;
+        }
+        if (PyImport_SetLazyImports(lazy_mode, NULL) < 0) {
+            return _PyStatus_ERR("failed to set lazy imports mode");
+        }
+    }
+    // If config->lazy_imports == -1, use the default mode (no change needed)
+
     if (is_main_interp) {
 #ifndef MS_WINDOWS
         emit_stderr_warning_for_legacy_locale(interp->runtime);

Python/sysmodule.c

@@ -3361,6 +3361,7 @@ static PyStructSequence_Field flags_fields[] = {
     {"gil",                     "-X gil"},
     {"thread_inherit_context",  "-X thread_inherit_context"},
     {"context_aware_warnings",    "-X context_aware_warnings"},
+    {"lazy_imports",            "-X lazy_imports"},
     {0}
 };
 
@@ -3370,7 +3371,7 @@ static PyStructSequence_Desc flags_desc = {
     "sys.flags",        /* name */
     flags__doc__,       /* doc */
     flags_fields,       /* fields */
-    18
+    19
 };
 
 static void
@@ -3463,6 +3464,7 @@ set_flags_from_config(PyInterpreterState *interp, PyObject *flags)
 #endif
     SetFlag(config->thread_inherit_context);
     SetFlag(config->context_aware_warnings);
+    SetFlag(config->lazy_imports);
 #undef SetFlagObj
 #undef SetFlag
     return 0;