From 8ff5dd251f4d29bd19f15dab6a731ddfe4ffb4bd Mon Sep 17 00:00:00 2001
From: Semyon Proshev <Semyon.Proshev@jetbrains.com>
Date: Thu, 8 Nov 2018 17:04:14 +0300
Subject: [PATCH] Result of `in` operation is always `bool` (PY-31956)

---
 .../python/psi/impl/PyBinaryExpressionImpl.java        |  3 +++
 python/testSrc/com/jetbrains/python/PyTypeTest.java    | 10 ++++++++++
 2 files changed, 13 insertions(+)

diff --git a/python/src/com/jetbrains/python/psi/impl/PyBinaryExpressionImpl.java b/python/src/com/jetbrains/python/psi/impl/PyBinaryExpressionImpl.java
index 6475201e2885..8a40a586c14d 100644
--- a/python/src/com/jetbrains/python/psi/impl/PyBinaryExpressionImpl.java
+++ b/python/src/com/jetbrains/python/psi/impl/PyBinaryExpressionImpl.java
@@ -136,6 +136,9 @@ public class PyBinaryExpressionImpl extends PyElementImpl implements PyBinaryExp
       }
       return PyUnionType.union(leftType, rightType);
     }
+
+    if (PyNames.CONTAINS.equals(getReferencedName())) return PyBuiltinCache.getInstance(this).getBoolType();
+
     final List<PyCallExpression.PyArgumentsMapping> results =
       PyCallExpressionHelper.mapArguments(this, PyResolveContext.noImplicits().withTypeEvalContext(context));
     if (!results.isEmpty()) {
diff --git a/python/testSrc/com/jetbrains/python/PyTypeTest.java b/python/testSrc/com/jetbrains/python/PyTypeTest.java
index 4e70b0e2d825..062ca6820333 100644
--- a/python/testSrc/com/jetbrains/python/PyTypeTest.java
+++ b/python/testSrc/com/jetbrains/python/PyTypeTest.java
@@ -3305,6 +3305,16 @@ public class PyTypeTest extends PyTestCase {
            "   expr = a");
   }
 
+  // PY-31956
+  public void testInAndNotBoolContains() {
+    doTest("bool",
+                   "class MyClass:\n" +
+                   "    def __contains__(self):\n" +
+                   "        return 42\n" +
+                   "\n" +
+                   "expr = 1 in MyClass()");
+  }
+
   // PY-32533
   public void testSuperWithAnotherType() {
     runWithLanguageLevel(