Problem: pip Python2.7 warning displayed too often

Solution: show it only once

CHANGES.rst

@@ -4,7 +4,9 @@ Change History
 3.0.0a2 (unreleased)
 ====================
 
--  Better patch for ``pkg_resources.Distribution.hashcmp`` performance.
+- Show only once pip warning about python version.
+
+- Better patch for ``pkg_resources.Distribution.hashcmp`` performance.
 
 
 3.0.0a1 (2020-05-17)

src/zc/buildout/easy_install.py

@@ -1659,6 +1659,17 @@ def call_pip_install(spec, dest):
 
     args.append(spec)
 
+    try:
+        from pip._internal.cli.cmdoptions import no_python_version_warning
+        HAS_WARNING_OPTION = True
+    except ImportError:
+        HAS_WARNING_OPTION = False
+    if HAS_WARNING_OPTION:
+        if not hasattr(call_pip_install, 'displayed'):
+            call_pip_install.displayed = True
+        else:
+            args.append('--no-python-version-warning')
+
     if level <= logging.DEBUG:
         logger.debug('Running pip install:\n"%s"\npath=%s\n',
                         '" "'.join(args), path)