Performance: remove __missing__() from production, it did repr(self)

Anytime there was a missing dict key (including all fields without "auth"),
__missing__() was called and did an repr(self.data) for developer assistance.
That happend more then 800 times per request.

Author: vdboor

src/schematools/types.py

@@ -7,6 +7,7 @@
 import json
 import logging
 import re
+import sys
 import typing
 import warnings
 from collections import UserDict
@@ -51,6 +52,12 @@
 
 logger = logging.getLogger(__name__)
 
+IS_DEBUGGER = (
+    "pytest" in sys.modules
+    or (sys.stdin and sys.stdin.isatty())
+    or (hasattr(sys, "gettrace") and sys.gettrace() is not None)
+)
+
 
 class SemVer(str):
     """Semantic version numbers.
@@ -208,8 +215,15 @@ def __deepcopy__(self, memo):
     def __repr__(self) -> str:
         return f"{self.__class__.__name__}({self.data!r})"
 
-    def __missing__(self, key: str) -> NoReturn:
-        raise KeyError(f"No field named '{key}' exists in {self!r}")
+    if IS_DEBUGGER:
+
+        def __missing__(self, key: str) -> NoReturn:
+            # This method would also be called by self.get("auth") for example,
+            # which makes such fail cases a bit slower than they have to be.
+            raise KeyError(
+                f"No field named '{key}' exists in {self.__class__.__name__},"
+                f" available are: {', '.join(self.keys())}"
+            )
 
 
 class SchemaType(JsonDict):