Drafting infer_fieldnames_from_function_return_type

minet/scrape/classes/function.py

@@ -1,16 +1,40 @@
-from typing import Optional, Callable, Any, cast, Dict
+from typing import Union, Optional, Callable, Any, cast, Dict, List
 
 import inspect
+
 from casanova import RowWrapper
 from bs4 import SoupStrainer
 
+from minet.types import get_type_hints, get_origin, get_args
 from minet.scrape.classes.base import ScraperBase
 from minet.scrape.soup import WonderfulSoup
 from minet.scrape.straining import strainer_from_css
 from minet.scrape.utils import ensure_soup
 from minet.scrape.types import AnyScrapableTarget
 
 
+def infer_fieldnames_from_function_return_type(fn: Callable) -> Optional[List[str]]:
+    if not callable(fn):
+        raise TypeError
+
+    return_type = get_type_hints(fn)["return"]
+
+    origin = get_origin(return_type)
+
+    if origin is Union:
+        args = get_args(return_type)
+
+        # Optionals
+        if len(args) == 2:
+            if args[1] is type(None):
+                return_type = args[0]
+
+    if return_type in (str, int, float, bool, type(None)):
+        return ["value"]
+
+    return None
+
+
 class FunctionScraper(ScraperBase):
     fn: Callable[[RowWrapper, WonderfulSoup], Any]
     fieldnames = None

test/scraper_test.py

@@ -1,6 +1,8 @@
 # =============================================================================
 # Minet Scrape Unit Tests
 # =============================================================================
+from typing import Optional
+
 import pytest
 from bs4 import BeautifulSoup, Tag, SoupStrainer
 from textwrap import dedent
@@ -31,6 +33,7 @@
     ScraperValidationMixedConcernError,
     ScraperValidationUnknownKeyError,
 )
+from minet.scrape.classes.function import infer_fieldnames_from_function_return_type
 
 BASIC_HTML = """
     <ul>
@@ -160,7 +163,7 @@
 """
 
 
-class TestDefinitionScraper(object):
+class TestDefinitionScraper:
     def test_basics(self):
         result = scrape({"iterator": "li"}, BASIC_HTML)
 
@@ -1055,3 +1058,31 @@ def clean(t):
         text = get_display_text(elements)
 
         assert text == "L'internationale."
+
+
+class TestFunctionScraper:
+    def test_infer_fieldnames_from_function_return_type(self):
+        def basic_string() -> str:
+            return "ok"
+
+        def basic_int() -> int:
+            return 4
+
+        def basic_float() -> float:
+            return 4.0
+
+        def basic_bool() -> bool:
+            return True
+
+        def basic_void() -> None:
+            return
+
+        def basic_optional_scalar() -> Optional[str]:
+            return
+
+        assert infer_fieldnames_from_function_return_type(basic_string) == ["value"]
+        assert infer_fieldnames_from_function_return_type(basic_int) == ["value"]
+        assert infer_fieldnames_from_function_return_type(basic_float) == ["value"]
+        assert infer_fieldnames_from_function_return_type(basic_bool) == ["value"]
+        assert infer_fieldnames_from_function_return_type(basic_void) == ["value"]
+        assert infer_fieldnames_from_function_return_type(basic_optional_scalar) == ["value"]