diff --git a/api-ref/source/conf.py b/api-ref/source/conf.py
index 0e19482061..e201186672 100644
--- a/api-ref/source/conf.py
+++ b/api-ref/source/conf.py
@@ -171,8 +171,8 @@ pygments_style = 'sphinx'
 git_cmd = ["git", "log", "--pretty=format:'%ad, commit %h'", "--date=local",
            "-n1"]
 try:
-    html_last_updated_fmt = subprocess.Popen(
-        git_cmd, stdout=subprocess.PIPE).communicate()[0]
+    html_last_updated_fmt = subprocess.check_output(
+        git_cmd).decode('utf-8')
 except Exception:
     warnings.warn('Cannot get last updated time from git repository. '
                   'Not setting "html_last_updated_fmt".')
diff --git a/doc/ext/support_matrix.py b/doc/ext/support_matrix.py
index c7e14046cd..c7e53fc13b 100644
--- a/doc/ext/support_matrix.py
+++ b/doc/ext/support_matrix.py
@@ -319,8 +319,7 @@ class SupportMatrixDirective(rst.Directive):
         summaryhead.append(header)
 
         # then one column for each hypervisor driver
-        impls = matrix.targets.keys()
-        impls.sort()
+        impls = sorted(matrix.targets.keys())
         for key in impls:
             target = matrix.targets[key]
             implcol = nodes.entry()
@@ -352,8 +351,7 @@ class SupportMatrixDirective(rst.Directive):
                 classes=["sp_feature_" + feature.status]))
 
             # and then one column for each hypervisor driver
-            impls = matrix.targets.keys()
-            impls.sort()
+            impls = sorted(matrix.targets.keys())
             for key in impls:
                 target = matrix.targets[key]
                 impl = feature.implementations[key]
diff --git a/doc/source/conf.py b/doc/source/conf.py
index 755652e93f..6cf48b5729 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -167,8 +167,8 @@ html_static_path = ['_static']
 git_cmd = ["git", "log", "--pretty=format:'%ad, commit %h'", "--date=local",
            "-n1"]
 try:
-    html_last_updated_fmt = subprocess.Popen(
-        git_cmd, stdout=subprocess.PIPE).communicate()[0]
+    html_last_updated_fmt = subprocess.check_output(
+        git_cmd).decode('utf-8')
 except Exception:
     warnings.warn('Cannot get last updated time from git repository. '
                   'Not setting "html_last_updated_fmt".')