fix(pacmak): Generate Relative Module Imports in Python

packages/jsii-pacmak/lib/targets/python.ts

@@ -25,6 +25,7 @@ import {
   PythonImports,
   mergePythonImports,
   toPackageName,
+  toPythonFqn,
 } from './python/type-name';
 import { die, toPythonIdentifier } from './python/util';
 import { toPythonVersionRange, toReleaseVersion } from './version-utils';
@@ -1673,7 +1674,26 @@ class PythonModule implements PythonType {
       for (const module of this.modules.sort((l, r) =>
         l.pythonName.localeCompare(r.pythonName),
       )) {
-        code.line(`import ${module.pythonName}`);
+        // Rather than generating an absolute import like
+        // "import jsii_calc.submodule.nested_submodule.deeply_nested"
+        // this builds a relative import like
+        // "from .submodule.nested_submodule import deeply_nested"
+        // This enables distributing python packages and using the
+        // generated modules in the same codebase.
+        const assemblyName = toPythonFqn(
+          module.assembly.name,
+          module.assembly,
+        ).pythonFqn;
+
+        const submodule = module.pythonName
+          .replace(`${assemblyName}.`, '')
+          .split('.');
+
+        const submodulePath = submodule
+          .slice(0, submodule.length - 1)
+          .join('.');
+        const submoduleName = submodule[submodule.length - 1];
+        code.line(`from .${submodulePath} import ${submoduleName}`);
       }
     }
   }

packages/jsii-pacmak/lib/targets/python/type-name.ts

@@ -373,7 +373,7 @@ class UserType implements TypeName {
   }
 }
 
-function toPythonFqn(fqn: string, rootAssm: Assembly) {
+export function toPythonFqn(fqn: string, rootAssm: Assembly) {
   const { assemblyName, packageName, tail } = getPackageName(fqn, rootAssm);
   const fqnParts: string[] = [packageName];