diff --git a/langkit/templates/python_api/module_py.mako b/langkit/templates/python_api/module_py.mako
index 3043d6cc6..56a711d05 100644
--- a/langkit/templates/python_api/module_py.mako
+++ b/langkit/templates/python_api/module_py.mako
@@ -1873,16 +1873,26 @@ class App(object):
         """
         return ""
 
-    def __init__(self):
+    def __init__(self, args=None):
         self.parser = argparse.ArgumentParser(description=self.description)
         self.parser.add_argument('files', nargs='+', help='Files')
         self.add_arguments()
-        self.args = self.parser.parse_args()
+
+        # Parse command line arguments
+        self.args = self.parser.parse_args(args)
+
         self.ctx = AnalysisContext(
             'utf-8', with_trivia=True,
             unit_provider=self.create_unit_provider()
         )
 
+        # Parse files
+        self.units = {}
+        for file_name in self.args.files:
+            self.u = self.ctx.get_from_file(file_name)
+            self.units[file_name] = self.u
+
+
     def add_arguments(self):
         """
         Hook for subclasses to add arguments to self.parser. Default
@@ -1897,23 +1907,26 @@ class App(object):
         """
         return None
 
-    def process_files(self):
+    def main(self):
         """
-        Load units for all source files on the command-line in `self.units`.
-        Put the last one in `self.u`.
+        Default implementation for App.main: just iterates on every units and
+        call ``process_unit`` on it.
         """
-        self.units = {}
-        for file_name in self.args.files:
-            self.u = self.ctx.get_from_file(file_name)
-            self.units[file_name] = self.u
+        for u in sorted(self.units.values(), key=lambda u: u.filename):
+            self.process_unit(u)
+
+    def process_unit(self, unit):
+        """
+        Abstract method that processes one unit. Needs to be subclassed by
+        implementors.
+        """
+        raise NotImplementedError()
 
     @classmethod
-    def run(cls):
+    def run(cls, args=None):
         """
         Instantiate and run this application.
         """
-        instance = cls()
-        instance.process_files()
-        instance.main()
+        cls(args).main()
 
     ${exts.include_extension(ctx.ext('python_api/app_exts'))}
diff --git a/langkit/templates/python_api/module_pyi.mako b/langkit/templates/python_api/module_pyi.mako
index 7e3b66dc4..c506d3889 100644
--- a/langkit/templates/python_api/module_pyi.mako
+++ b/langkit/templates/python_api/module_pyi.mako
@@ -417,12 +417,12 @@ class App(object):
     @property
     def description(self) -> str: ...
 
-    def __init__(self) -> None: ...
+    def __init__(self, args: Opt[List[str]]) -> None: ...
     def add_arguments(self) -> None: ...
     def create_unit_provider(self) -> Opt[UnitProvider]: ...
-    def process_files(self) -> None: ...
+    def process_unit(self, unit: AnalysisUnit) -> None: ...
 
     @classmethod
-    def run(cls) -> None: ...
+    def run(cls, args: Opt[List[str]]=None) -> None: ...
 
     ${exts.include_extension(ctx.ext('python_api', 'mypy_app_exts'))}
diff --git a/testsuite/tests/python_api/python_app/expected_concrete_syntax.lkt b/testsuite/tests/python_api/python_app/expected_concrete_syntax.lkt
new file mode 100644
index 000000000..6a542a954
--- /dev/null
+++ b/testsuite/tests/python_api/python_app/expected_concrete_syntax.lkt
@@ -0,0 +1,12 @@
+import lexer_example
+@with_lexer(foo_lexer)
+grammar foo_grammar {
+    @main_rule main_rule <- Example("example")
+
+}
+
+@abstract class FooNode : Node {
+}
+
+class Example : FooNode implements TokenNode {
+}
diff --git a/testsuite/tests/python_api/python_app/input1 b/testsuite/tests/python_api/python_app/input1
new file mode 100644
index 000000000..7e0df6c35
--- /dev/null
+++ b/testsuite/tests/python_api/python_app/input1
@@ -0,0 +1 @@
+example hello1
diff --git a/testsuite/tests/python_api/python_app/input2 b/testsuite/tests/python_api/python_app/input2
new file mode 100644
index 000000000..c48ed16fb
--- /dev/null
+++ b/testsuite/tests/python_api/python_app/input2
@@ -0,0 +1 @@
+example hello2
diff --git a/testsuite/tests/python_api/python_app/input3 b/testsuite/tests/python_api/python_app/input3
new file mode 100644
index 000000000..42896c274
--- /dev/null
+++ b/testsuite/tests/python_api/python_app/input3
@@ -0,0 +1 @@
+example hello3
diff --git a/testsuite/tests/python_api/python_app/main.py b/testsuite/tests/python_api/python_app/main.py
new file mode 100644
index 000000000..2316408ec
--- /dev/null
+++ b/testsuite/tests/python_api/python_app/main.py
@@ -0,0 +1,10 @@
+import libfoolang as lfl
+
+
+class App(lfl.App):
+    def process_unit(self, unit):
+        unit.root.dump()
+
+
+if __name__ == '__main__':
+    App.run(['input3', 'input1', 'input2'])
diff --git a/testsuite/tests/python_api/python_app/test.out b/testsuite/tests/python_api/python_app/test.out
new file mode 100644
index 000000000..b7be86591
--- /dev/null
+++ b/testsuite/tests/python_api/python_app/test.out
@@ -0,0 +1,4 @@
+Example input1:1:1-1:8: example
+Example input2:1:1-1:8: example
+Example input3:1:1-1:8: example
+Done
diff --git a/testsuite/tests/python_api/python_app/test.py b/testsuite/tests/python_api/python_app/test.py
new file mode 100644
index 000000000..00bef6f86
--- /dev/null
+++ b/testsuite/tests/python_api/python_app/test.py
@@ -0,0 +1,20 @@
+"""
+Test python App class.
+"""
+
+from langkit.dsl import ASTNode
+
+from utils import build_and_run
+
+
+class FooNode(ASTNode):
+    pass
+
+
+class Example(FooNode):
+    token_node = True
+
+
+build_and_run(lkt_file='expected_concrete_syntax.lkt', py_script='main.py',
+              types_from_lkt=True)
+print('Done')
diff --git a/testsuite/tests/python_api/python_app/test.yaml b/testsuite/tests/python_api/python_app/test.yaml
new file mode 100644
index 000000000..30423a038
--- /dev/null
+++ b/testsuite/tests/python_api/python_app/test.yaml
@@ -0,0 +1 @@
+driver: python