Improve type checker performance (#13094)

* conditional declare `TOKENIZER_MAPPING_NAMES` within a `if TYPE_CHECKING` block so that type checkers dont need to evaluate the RHS of the assignment.

this improves performance of the pylance/pyright type checkers

* Update src/transformers/models/auto/tokenization_auto.py
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* adding missing import

* format
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

src/transformers/models/auto/tokenization_auto.py

@@ -18,7 +18,7 @@ import importlib
 import json
 import os
 from collections import OrderedDict
-from typing import Dict, Optional, Union
+from typing import TYPE_CHECKING, Dict, Optional, Tuple, Union
 
 from ...configuration_utils import PretrainedConfig
 from ...file_utils import (
@@ -43,8 +43,12 @@ from .configuration_auto import (
 
 logger = logging.get_logger(__name__)
 
-
-TOKENIZER_MAPPING_NAMES = OrderedDict(
+if TYPE_CHECKING:
+    # This significantly improves completion suggestion performance when
+    # the transformers package is used with Microsoft's Pylance language server.
+    TOKENIZER_MAPPING_NAMES: OrderedDict[str, Tuple[Optional[str], Optional[str]]] = OrderedDict()
+else:
+    TOKENIZER_MAPPING_NAMES = OrderedDict(
         [
             ("retribert", ("RetriBertTokenizer", "RetriBertTokenizerFast" if is_tokenizers_available() else None)),
             ("roformer", ("RoFormerTokenizer", "RoFormerTokenizerFast" if is_tokenizers_available() else None)),
@@ -118,9 +122,15 @@ TOKENIZER_MAPPING_NAMES = OrderedDict(
             ("layoutlm", ("LayoutLMTokenizer", "LayoutLMTokenizerFast" if is_tokenizers_available() else None)),
             (
                 "dpr",
-            ("DPRQuestionEncoderTokenizer", "DPRQuestionEncoderTokenizerFast" if is_tokenizers_available() else None),
+                (
+                    "DPRQuestionEncoderTokenizer",
+                    "DPRQuestionEncoderTokenizerFast" if is_tokenizers_available() else None,
+                ),
+            ),
+            (
+                "squeezebert",
+                ("SqueezeBertTokenizer", "SqueezeBertTokenizerFast" if is_tokenizers_available() else None),
             ),
-        ("squeezebert", ("SqueezeBertTokenizer", "SqueezeBertTokenizerFast" if is_tokenizers_available() else None)),
             ("bert", ("BertTokenizer", "BertTokenizerFast" if is_tokenizers_available() else None)),
             ("openai-gpt", ("OpenAIGPTTokenizer", "OpenAIGPTTokenizerFast" if is_tokenizers_available() else None)),
             ("gpt2", ("GPT2Tokenizer", "GPT2TokenizerFast" if is_tokenizers_available() else None)),
@@ -189,7 +199,7 @@ TOKENIZER_MAPPING_NAMES = OrderedDict(
                 ),
             ),
         ]
-)
+    )
 
 TOKENIZER_MAPPING = _LazyAutoMapping(CONFIG_MAPPING_NAMES, TOKENIZER_MAPPING_NAMES)