From: Daniele Varrazzo <daniele.varrazzo@gmail.com>
Date: Wed, 2 Mar 2022 00:48:30 +0000 (+0000)
Subject: fix: don't raise error accessing Cursor.description after COPY_OUT
X-Git-Tag: 3.1~175
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=59a1c99aff818a37ba5e53b4adad28670a757bdf;p=thirdparty%2Fpsycopg.git

fix: don't raise error accessing Cursor.description after COPY_OUT

COPY_OUT result advertises the number of columns but not their names (or
types). Use a surrogate name for description (which is more useful than
returning `None`, because at lest it tells how many columns were
emitted).

Close #235.
---

diff --git a/docs/news.rst b/docs/news.rst
index f96a54752..e03f04cfe 100644
--- a/docs/news.rst
+++ b/docs/news.rst
@@ -26,6 +26,8 @@ Psycopg 3.0.10 (unreleased)
 
 - Leave the connection working after interrupting a query with Ctrl-C
   (currently only for sync connections, :ticket:`#231`).
+- Fix `Cursor.description` after a COPY ... TO STDOUT operation
+  (:ticket:`#235`).
 
 
 Current release
diff --git a/psycopg/psycopg/_column.py b/psycopg/psycopg/_column.py
index ab30b4d4f..9e4e7357c 100644
--- a/psycopg/psycopg/_column.py
+++ b/psycopg/psycopg/_column.py
@@ -7,8 +7,6 @@ The Column object in Cursor.description
 from typing import Any, NamedTuple, Optional, Sequence, TYPE_CHECKING
 from operator import attrgetter
 
-from . import errors as e
-
 if TYPE_CHECKING:
     from .cursor import BaseCursor
 
@@ -28,10 +26,11 @@ class Column(Sequence[Any]):
         assert res
 
         fname = res.fname(index)
-        if not fname:
-            raise e.InterfaceError(f"no name available for column {index}")
-
-        self._name = fname.decode(cursor._encoding)
+        if fname:
+            self._name = fname.decode(cursor._encoding)
+        else:
+            # COPY_OUT results have columns but no name
+            self._name = f"column_{index + 1}"
 
         self._data = ColumnData(
             ftype=res.ftype(index),
diff --git a/tests/test_copy.py b/tests/test_copy.py
index af541a256..4cea6646a 100644
--- a/tests/test_copy.py
+++ b/tests/test_copy.py
@@ -533,6 +533,19 @@ def test_str(conn):
     assert "[INTRANS]" in str(copy)
 
 
+def test_description(conn):
+    with conn.cursor() as cur:
+        with cur.copy("copy (select 'This', 'Is', 'Text') to stdout") as copy:
+            len(cur.description) == 3
+            assert cur.description[0].name == "column_1"
+            assert cur.description[2].name == "column_3"
+            list(copy.rows())
+
+        len(cur.description) == 3
+        assert cur.description[0].name == "column_1"
+        assert cur.description[2].name == "column_3"
+
+
 @pytest.mark.parametrize(
     "format, buffer",
     [(Format.TEXT, "sample_text"), (Format.BINARY, "sample_binary")],
diff --git a/tests/test_copy_async.py b/tests/test_copy_async.py
index a5cfd605e..ba025e1a0 100644
--- a/tests/test_copy_async.py
+++ b/tests/test_copy_async.py
@@ -532,6 +532,19 @@ async def test_str(aconn):
     assert "[INTRANS]" in str(copy)
 
 
+async def test_description(aconn):
+    async with aconn.cursor() as cur:
+        async with cur.copy("copy (select 'This', 'Is', 'Text') to stdout") as copy:
+            len(cur.description) == 3
+            assert cur.description[0].name == "column_1"
+            assert cur.description[2].name == "column_3"
+            await alist(copy.rows())
+
+        len(cur.description) == 3
+        assert cur.description[0].name == "column_1"
+        assert cur.description[2].name == "column_3"
+
+
 @pytest.mark.parametrize(
     "format, buffer",
     [(Format.TEXT, "sample_text"), (Format.BINARY, "sample_binary")],