feat: classify conditional imports

BACKLOG.md

@@ -20,7 +20,7 @@ This backlog collects product and maintenance ideas from project research.
 
 - Add support for namespace packages that do not contain `__init__.py`.
 - Detect dynamic imports such as `importlib.import_module()` and `__import__()`.
-- Detect conditional imports such as `try/except ImportError`.
+- [x] Detect conditional imports such as `try/except ImportError`.
 - Add better `TYPE_CHECKING` import handling, including options to ignore, include, or report type-only imports separately.
 - Improve external dependency rules so users can express allowed and forbidden third-party packages at module or slice level.
 - Consider a public-interface rule inspired by Tach, where modules may only import through declared package APIs.

README.md

@@ -345,6 +345,15 @@ ArchUnitPython detects string-based dynamic imports such as `importlib.import_mo
 from my_app.adapters.sql import Repository  # archunit: ignore
 ```
 
+### Conditional Imports
+
+Imports inside `try` blocks that handle `ImportError` or
+`ModuleNotFoundError` are marked as conditional dependencies. This helps graph
+reports distinguish optional imports and fallback implementations from regular
+runtime imports. Conditional dependencies remain part of architecture checks;
+relative and dynamic imports also retain their original import kind in graph
+reports.
+
 ### Naming Conventions
 
 ```python

src/archunitpython/common/extraction/extract_graph.py

@@ -43,6 +43,7 @@ class _LocatedImport:
     module_name: str
     import_kind: ImportKind
     line_number: int
+    resolution_kind: ImportKind | None = None
 
 
 @dataclass(frozen=True)
@@ -182,8 +183,9 @@ def _extract_graph_uncached(
                 and import_kind == ImportKind.TYPE_IMPORT
             ):
                 continue
+            resolution_kind = located_import.resolution_kind or import_kind
             resolved, is_external = _resolve_import(
-                module_name, file_path, project_path, import_kind
+                module_name, file_path, project_path, resolution_kind
             )
             if resolved and resolved != _normalize(file_path):
                 # Check if the resolved path is in our project
@@ -195,7 +197,7 @@ def _extract_graph_uncached(
                         source=_normalize(file_path),
                         target=resolved,
                         external=is_external,
-                        import_kinds=(import_kind,),
+                        import_kinds=_edge_import_kinds(located_import),
                     )
                 )
 
@@ -299,32 +301,56 @@ def _extract_located_imports(file_path: str) -> list[_LocatedImport]:
     imports: list[_LocatedImport] = []
     ignore_directives = _find_ignore_directives(source)
     type_checking_ranges = _find_type_checking_ranges(tree)
+    conditional_import_ranges = _find_conditional_import_ranges(tree)
 
     for node in ast.walk(tree):
         if isinstance(node, ast.Import):
-            is_type = _in_type_checking(node, type_checking_ranges)
-            kind = ImportKind.TYPE_IMPORT if is_type else ImportKind.IMPORT
+            syntax_kind = ImportKind.IMPORT
+            kind = _classify_import(
+                node,
+                syntax_kind,
+                type_checking_ranges,
+                conditional_import_ranges,
+            )
             for alias in node.names:
-                imports.append(_LocatedImport(alias.name, kind, node.lineno))
+                imports.append(
+                    _LocatedImport(alias.name, kind, node.lineno, syntax_kind)
+                )
 
         elif isinstance(node, ast.ImportFrom):
-            is_type = _in_type_checking(node, type_checking_ranges)
-            if node.level and node.level > 0:
-                # Relative import
-                kind = ImportKind.TYPE_IMPORT if is_type else ImportKind.RELATIVE_IMPORT
-                module = node.module or ""
-                dots = "." * node.level
-                imports.append(_LocatedImport(f"{dots}{module}", kind, node.lineno))
-            else:
-                kind = ImportKind.TYPE_IMPORT if is_type else ImportKind.FROM_IMPORT
-                if node.module:
-                    imports.append(_LocatedImport(node.module, kind, node.lineno))
+            syntax_kind = (
+                ImportKind.RELATIVE_IMPORT
+                if node.level and node.level > 0
+                else ImportKind.FROM_IMPORT
+            )
+            kind = _classify_import(
+                node,
+                syntax_kind,
+                type_checking_ranges,
+                conditional_import_ranges,
+            )
+            for module_name in _import_from_module_names(node):
+                imports.append(
+                    _LocatedImport(
+                        module_name,
+                        kind,
+                        node.lineno,
+                        syntax_kind,
+                    )
+                )
 
         elif isinstance(node, ast.Call):
-            is_type = _in_type_checking(node, type_checking_ranges)
-            kind = ImportKind.TYPE_IMPORT if is_type else ImportKind.DYNAMIC_IMPORT
+            syntax_kind = ImportKind.DYNAMIC_IMPORT
+            kind = _classify_import(
+                node,
+                syntax_kind,
+                type_checking_ranges,
+                conditional_import_ranges,
+            )
             for module_name in _extract_dynamic_import_names(node):
-                imports.append(_LocatedImport(module_name, kind, node.lineno))
+                imports.append(
+                    _LocatedImport(module_name, kind, node.lineno, syntax_kind)
+                )
 
     return [
         import_
@@ -389,6 +415,43 @@ def _extract_dynamic_import_names(node: ast.Call) -> list[str]:
     return []
 
 
+def _import_from_module_names(node: ast.ImportFrom) -> tuple[str, ...]:
+    """Return resolvable module names for a from-import statement."""
+    dots = "." * (node.level or 0)
+    if node.module:
+        return (f"{dots}{node.module}",)
+
+    aliases = tuple(alias.name for alias in node.names if alias.name != "*")
+    if dots and aliases:
+        return tuple(f"{dots}{alias}" for alias in aliases)
+    return (dots,) if dots else ()
+
+
+def _edge_import_kinds(import_: _LocatedImport) -> tuple[ImportKind, ...]:
+    """Return graph labels without losing syntax for conditional imports."""
+    resolution_kind = import_.resolution_kind or import_.import_kind
+    if (
+        import_.import_kind == ImportKind.CONDITIONAL_IMPORT
+        and resolution_kind != import_.import_kind
+    ):
+        return (resolution_kind, import_.import_kind)
+    return (import_.import_kind,)
+
+
+def _classify_import(
+    node: ast.AST,
+    default_kind: ImportKind,
+    type_checking_ranges: list[tuple[int, int]],
+    conditional_import_ranges: list[tuple[int, int]],
+) -> ImportKind:
+    """Classify an import node by special context before syntax kind."""
+    if _in_type_checking(node, type_checking_ranges):
+        return ImportKind.TYPE_IMPORT
+    if _in_conditional_import(node, conditional_import_ranges):
+        return ImportKind.CONDITIONAL_IMPORT
+    return default_kind
+
+
 def _find_type_checking_ranges(tree: ast.Module) -> list[tuple[int, int]]:
     """Find line ranges of TYPE_CHECKING blocks."""
     ranges: list[tuple[int, int]] = []
@@ -414,6 +477,46 @@ def _find_type_checking_ranges(tree: ast.Module) -> list[tuple[int, int]]:
     return sorted(ranges, key=lambda ele: ele[0])
 
 
+def _find_conditional_import_ranges(tree: ast.Module) -> list[tuple[int, int]]:
+    """Find try/except ImportError ranges that contain optional imports."""
+    ranges: list[tuple[int, int]] = []
+
+    for node in ast.walk(tree):
+        if not isinstance(node, ast.Try):
+            continue
+        if not any(_handles_import_error(handler.type) for handler in node.handlers):
+            continue
+
+        ranges.extend(_statement_ranges(node.body))
+        for handler in node.handlers:
+            if _handles_import_error(handler.type):
+                ranges.extend(_statement_ranges(handler.body))
+
+    return sorted(ranges, key=lambda ele: ele[0])
+
+
+def _handles_import_error(node: ast.expr | None) -> bool:
+    """Return True if an except handler catches import-related errors."""
+    if node is None:
+        return False
+    if isinstance(node, ast.Name):
+        return node.id in {"ImportError", "ModuleNotFoundError"}
+    if isinstance(node, ast.Attribute):
+        return node.attr in {"ImportError", "ModuleNotFoundError"}
+    if isinstance(node, ast.Tuple):
+        return any(_handles_import_error(elt) for elt in node.elts)
+    return False
+
+
+def _statement_ranges(statements: list[ast.stmt]) -> list[tuple[int, int]]:
+    """Return line ranges covered by statement blocks."""
+    if not statements:
+        return []
+    start = statements[0].lineno
+    end = max(getattr(statement, "end_lineno", statement.lineno) for statement in statements)
+    return [(start, end)]
+
+
 def _in_type_checking(node: ast.AST, ranges: list[tuple[int, int]]) -> bool:
     """Check if a node is inside a TYPE_CHECKING block."""
     if not hasattr(node, "lineno"):
@@ -422,6 +525,14 @@ def _in_type_checking(node: ast.AST, ranges: list[tuple[int, int]]) -> bool:
     return any(start <= lineno <= end for start, end in ranges)
 
 
+def _in_conditional_import(node: ast.AST, ranges: list[tuple[int, int]]) -> bool:
+    """Check if a node is inside a try/except ImportError block."""
+    if not hasattr(node, "lineno"):
+        return False
+    lineno = node.lineno
+    return any(start <= lineno <= end for start, end in ranges)
+
+
 def _resolve_import(
     import_name: str,
     source_file: str,
@@ -433,7 +544,15 @@ def _resolve_import(
     Returns (resolved_path, is_external).
     The path is normalized with forward slashes.
     """
-    if kind in (ImportKind.RELATIVE_IMPORT, ImportKind.TYPE_IMPORT) and import_name.startswith("."):
+    if (
+        kind
+        in (
+            ImportKind.RELATIVE_IMPORT,
+            ImportKind.TYPE_IMPORT,
+            ImportKind.CONDITIONAL_IMPORT,
+        )
+        and import_name.startswith(".")
+    ):
         # Relative import
         return _resolve_relative_import(import_name, source_file, project_root)
 

src/archunitpython/common/extraction/graph.py

@@ -14,6 +14,7 @@ class ImportKind(Enum):
     RELATIVE_IMPORT = "relative"  # from . import bar / from ..foo import bar
     DYNAMIC_IMPORT = "dynamic"  # __import__('foo') / importlib.import_module()
     TYPE_IMPORT = "type"  # inside TYPE_CHECKING block
+    CONDITIONAL_IMPORT = "conditional"  # inside try/except ImportError
 
 
 @dataclass(frozen=True)