Reduce import time by removing string and tomli._types imports

pyproject.toml

@@ -102,6 +102,12 @@ commands = [
     ["python", "benchmark/run.py"],
 ]
 
+[tool.tox.env."benchmark-import"]
+description = "Measure module import times. Tox sends Python output to stderr, so to filter use e.g. `tox -e benchmark-import 2> >(grep tomli)`."
+commands = [
+    ["python", "-X", "importtime", "-c", "import tomli"],
+]
+
 [tool.tox.env."fuzz"]
 description = 'run the fuzzer against a local Tomli version (needs "apt install clang")'
 deps = [

src/tomli/_parser.py

@@ -4,12 +4,9 @@
 
 from __future__ import annotations
 
-from collections.abc import Iterable
-import string
 import sys
 from types import MappingProxyType
-from typing import IO, Any, Final, NamedTuple
-import warnings
+from typing import IO, TYPE_CHECKING, Any, Final, NamedTuple
 
 from ._re import (
     RE_DATETIME,
@@ -19,7 +16,11 @@
     match_to_localtime,
     match_to_number,
 )
-from ._types import Key, ParseFloat, Pos
+
+if TYPE_CHECKING:
+    from collections.abc import Iterable
+
+    from ._types import Key, ParseFloat, Pos
 
 # Inline tables/arrays are implemented using recursion. Pathologically
 # nested documents cause pure Python to raise RecursionError (which is OK),
@@ -46,9 +47,11 @@
 
 TOML_WS: Final = frozenset(" \t")
 TOML_WS_AND_NEWLINE: Final = TOML_WS | frozenset("\n")
-BARE_KEY_CHARS: Final = frozenset(string.ascii_letters + string.digits + "-_")
+BARE_KEY_CHARS: Final = frozenset(
+    "abcdefghijklmnopqrstuvwxyz" "ABCDEFGHIJKLMNOPQRSTUVWXYZ" "0123456789" "-_"
+)
 KEY_INITIAL_CHARS: Final = BARE_KEY_CHARS | frozenset("\"'")
-HEXDIGIT_CHARS: Final = frozenset(string.hexdigits)
+HEXDIGIT_CHARS: Final = frozenset("abcdef" "ABCDEF" "0123456789")
 
 BASIC_STR_ESCAPE_REPLACEMENTS: Final = MappingProxyType(
     {
@@ -92,6 +95,8 @@ def __init__(
             or not isinstance(doc, str)
             or not isinstance(pos, int)
         ):
+            import warnings
+
             warnings.warn(
                 "Free-form arguments for TOMLDecodeError are deprecated. "
                 "Please set 'msg' (str), 'doc' (str) and 'pos' (int) arguments only.",

src/tomli/_re.py

@@ -7,9 +7,10 @@
 from datetime import date, datetime, time, timedelta, timezone, tzinfo
 from functools import lru_cache
 import re
-from typing import Any, Final
+from typing import TYPE_CHECKING, Any, Final
 
-from ._types import ParseFloat
+if TYPE_CHECKING:
+    from ._types import ParseFloat
 
 # E.g.
 # - 00:32:00.999999

tests/test_misc.py

@@ -5,6 +5,7 @@
 import copy
 import datetime
 from decimal import Decimal as D
+import importlib
 from pathlib import Path
 import sys
 import tempfile
@@ -128,3 +129,11 @@ def test_inline_table_recursion_limit(self):
             r"TOML inline arrays/tables are nested more than the allowed [0-9]+ levels",
         ):
             tomllib.loads(recursive_table_toml)
+
+    def test_types_import(self):
+        """Test that `_types` module runs.
+
+        The module is for type annotations only, so it is otherwise
+        never imported by tests.
+        """
+        importlib.import_module(f"{tomllib.__name__}._types")