fix: restore pre-3.1 behaviour converting fields to named tuples attributes

Let more valid identifiers through _as_python_identifier(). Also 2.5x faster if no change is needed

Close #386

diff --git a/psycopg/psycopg/_encodings.py b/psycopg/psycopg/_encodings.py
index d293949e34d13835608b8214d02f7d1e6f4dfe5d..b1b21267c5c25a4c4bd6706bbfd60f1036c2c0db 100644 (file)
--- a/psycopg/psycopg/_encodings.py
+++ b/psycopg/psycopg/_encodings.py
@@ -146,10 +146,13 @@ def _as_python_identifier(s: str, prefix: str = "f") -> str:
     Replace all non-valid chars with '_' and prefix the value with *prefix* if
     the first letter is an '_'.
     """
-    s = _re_clean.sub("_", s)
-    # Python identifier cannot start with numbers, namedtuple fields
-    # cannot start with underscore. So...
-    if s[0] == "_" or "0" <= s[0] <= "9":
+    if not s.isidentifier():
+        if s[0] in "1234567890":
+            s = prefix + s
+        if not s.isidentifier():
+            s = _re_clean.sub("_", s)
+    # namedtuple fields cannot start with underscore. So...
+    if s[0] == "_":
         s = prefix + s
     return s