AP: Use Py7.

[skip travis] [skip appveyor]

azure-pipelines.yml

@@ -19,6 +19,11 @@ jobs:
         TEST_TOOLSET: gcc
         CXX: g++-8
   steps:
+  - task: UsePythonVersion@0
+    inputs:
+      versionSpec: '2.7'
+      architecture: 'x64'
+      addToPath: true
   - bash: |
         set -e
         uname -a
@@ -51,6 +56,11 @@ jobs:
         TOOLSET: vc141
         TEST_TOOLSET: msvc
   steps:
+  - task: UsePythonVersion@0
+    inputs:
+      versionSpec: '2.7'
+      architecture: 'x64'
+      addToPath: true
   - powershell: |
         cd src/engine
         $env:path += ';' + $env:CXX_PATH