subprocess_fixed: Gracefully handle platforms without subprocess.Popen.

mgiuca-google · mgiuca-google · commit b29c93c1c5cf · 2013-03-20T10:37:49.000+11:00
If subprocess.Popen is missing (for example, on Google App Engine), replaces it
with a dummy version that raises OSError. In these environments, calls to
subprocess will be handled properly as if the called app could not be found,
instead of raising AttributeError.
diff --git a/lib/matplotlib/subprocess_fixed.py b/lib/matplotlib/subprocess_fixed.py
@@ -3,6 +3,8 @@
 work-arounds:
 - Provides the check_output function (which subprocess only provides from Python
   2.7 onwards).
+- Provides a stub implementation of subprocess members on Google App Engine
+  (which are missing in subprocess).
 
 Instead of importing subprocess, other modules should use this as follows:
 
@@ -17,9 +19,19 @@
 
 __all__ = ['Popen', 'PIPE', 'STDOUT', 'check_output']
 
-Popen = subprocess.Popen
-PIPE = subprocess.PIPE
-STDOUT = subprocess.STDOUT
+
+if hasattr(subprocess, 'Popen'):
+    Popen = subprocess.Popen
+    # Assume that it also has the other constants.
+    PIPE = subprocess.PIPE
+    STDOUT = subprocess.STDOUT
+else:
+    # In restricted environments (such as Google App Engine), these are
+    # non-existent. Replace them with dummy versions that always raise OSError.
+    def Popen(*args, **kwargs):
+        raise OSError("subprocess.Popen is not supported")
+    PIPE = -1
+    STDOUT = -2
 
 
 def _check_output(*popenargs, **kwargs):
