diff --git a/src/CHANGES.txt b/src/CHANGES.txt
index 9c7e3b1746..94592f597e 100755
--- a/src/CHANGES.txt
+++ b/src/CHANGES.txt
@@ -11,6 +11,10 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
 
     - Whatever John Doe did.
 
+  From Mats Wichmann:
+    - Quiet open file ResourceWarnings on Python >= 3.6 caused by
+      not using a context manager around Popen.stdout
+
 
 RELEASE 3.0.4 - Mon, 20 Jan 2019 22:49:27 +0000
 
diff --git a/src/engine/SCons/Tool/gcc.py b/src/engine/SCons/Tool/gcc.py
index fabcc9697f..79b64f0605 100644
--- a/src/engine/SCons/Tool/gcc.py
+++ b/src/engine/SCons/Tool/gcc.py
@@ -68,32 +68,40 @@ def exists(env):
 
 def detect_version(env, cc):
     """Return the version of the GNU compiler, or None if it is not a GNU compiler."""
+    version = None
     cc = env.subst(cc)
     if not cc:
-        return None
-    version = None
+        return version
+
+    # -dumpversion was added in GCC 3.0.  As long as we're supporting
+    # GCC versions older than that, we should use --version and a
+    # regular expression.
     # pipe = SCons.Action._subproc(env, SCons.Util.CLVar(cc) + ['-dumpversion'],
     pipe = SCons.Action._subproc(env, SCons.Util.CLVar(cc) + ['--version'],
                                  stdin='devnull',
                                  stderr='devnull',
                                  stdout=subprocess.PIPE)
-    # -dumpversion was added in GCC 3.0.  As long as we're supporting
-    # GCC versions older than that, we should use --version and a
-    # regular expression.
-    # line = pipe.stdout.read().strip()
+    if pipe.wait() != 0:
+        return version
+
+    with pipe.stdout:
+        # -dumpversion variant:
+        # line = pipe.stdout.read().strip()
+        # --version variant:
+        line = SCons.Util.to_str(pipe.stdout.readline())
+        # Non-GNU compiler's output (like AIX xlc's) may exceed the stdout buffer:
+        # So continue with reading to let the child process actually terminate.
+        while SCons.Util.to_str(pipe.stdout.readline()):
+            pass
+
+    # -dumpversion variant:
     # if line:
-    #    version = line
-    line = SCons.Util.to_str(pipe.stdout.readline())
+    #     version = line
+    # --version variant:
     match = re.search(r'[0-9]+(\.[0-9]+)+', line)
     if match:
         version = match.group(0)
-    # Non-GNU compiler's output (like AIX xlc's) may exceed the stdout buffer:
-    # So continue with reading to let the child process actually terminate.
-    while SCons.Util.to_str(pipe.stdout.readline()):
-        pass
-    ret = pipe.wait()
-    if ret != 0:
-        return None
+
     return version
 
 # Local Variables:
diff --git a/src/engine/SCons/Tool/swig.py b/src/engine/SCons/Tool/swig.py
index 08881a01bd..77cfe1de41 100644
--- a/src/engine/SCons/Tool/swig.py
+++ b/src/engine/SCons/Tool/swig.py
@@ -135,21 +135,31 @@ def t_from_s(t, p, s, x):
 
 def _get_swig_version(env, swig):
     """Run the SWIG command line tool to get and return the version number"""
+    version = None
     swig = env.subst(swig)
+    if not swig:
+        return version
     pipe = SCons.Action._subproc(env, SCons.Util.CLVar(swig) + ['-version'],
                                  stdin = 'devnull',
                                  stderr = 'devnull',
                                  stdout = subprocess.PIPE)
-    if pipe.wait() != 0: return
+    if pipe.wait() != 0:
+        return version
 
     # MAYBE:   out = SCons.Util.to_str (pipe.stdout.read())
-    out = SCons.Util.to_str(pipe.stdout.read())
+    with pipe.stdout:
+        out = SCons.Util.to_str(pipe.stdout.read())
+
     match = re.search('SWIG Version\s+(\S+).*', out, re.MULTILINE)
     if match:
-        if verbose: print("Version is:%s"%match.group(1))
-        return match.group(1)
+        version = match.group(1)
+        if verbose:
+            print("Version is: %s" % version)
     else:
-        if verbose: print("Unable to detect version: [%s]"%out)
+        if verbose:
+            print("Unable to detect version: [%s]" % out)
+
+    return version
 
 def generate(env):
     """Add Builders and construction variables for swig to an Environment."""