Prefer exist_ok=True over explicit os.path.exists(...) checks (#16642)

This PR replaces explicit `os.path.exists(...)` checks with
`os.makedirs(..., exist_ok=True)` where possible.

This removes the need for an extra existence check and slightly
simplifies the code. This can also prevent race conditions like #16630.

Author: lgeiger

mypy/report.py

@@ -99,7 +99,7 @@ class AbstractReporter(metaclass=ABCMeta):
     def __init__(self, reports: Reports, output_dir: str) -> None:
         self.output_dir = output_dir
         if output_dir != "<memory>":
-            stats.ensure_dir_exists(output_dir)
+            os.makedirs(output_dir, exist_ok=True)
 
     @abstractmethod
     def on_file(
@@ -737,7 +737,7 @@ def on_file(
         if path.startswith(".."):
             return
         out_path = os.path.join(self.output_dir, "xml", path + ".xml")
-        stats.ensure_dir_exists(os.path.dirname(out_path))
+        os.makedirs(os.path.dirname(out_path), exist_ok=True)
         last_xml.write(out_path, encoding="utf-8")
 
     def on_finish(self) -> None:
@@ -782,7 +782,7 @@ def on_file(
         if path.startswith(".."):
             return
         out_path = os.path.join(self.output_dir, "html", path + ".html")
-        stats.ensure_dir_exists(os.path.dirname(out_path))
+        os.makedirs(os.path.dirname(out_path), exist_ok=True)
         transformed_html = bytes(self.xslt_html(last_xml, ext=self.param_html))
         with open(out_path, "wb") as out_file:
             out_file.write(transformed_html)

mypy/stats.py

@@ -477,11 +477,6 @@ def is_complex(t: Type) -> bool:
     return is_generic(t) or isinstance(t, (FunctionLike, TupleType, TypeVarType))
 
 
-def ensure_dir_exists(dir: str) -> None:
-    if not os.path.exists(dir):
-        os.makedirs(dir)
-
-
 def is_special_form_any(t: AnyType) -> bool:
     return get_original_any(t).type_of_any == TypeOfAny.special_form
 

mypy/stubgen.py

@@ -1833,8 +1833,7 @@ def parse_options(args: list[str]) -> Options:
         parser.error("Cannot specify both --parse-only/--no-analysis and --inspect-mode")
 
     # Create the output folder if it doesn't already exist.
-    if not os.path.exists(ns.output_dir):
-        os.makedirs(ns.output_dir)
+    os.makedirs(ns.output_dir, exist_ok=True)
 
     return Options(
         pyversion=pyversion,