X-Git-Url: http://xvm.mit.edu/gitweb/invirt/packages/invirt-base.git/blobdiff_plain/fa8280e5dab14d66b4a2f5c98151afbd9868f33d..efe0510028323cd64653d5b7195e8c4d4ca1455e:/python/invirt/common.py

diff --git a/python/invirt/common.py b/python/invirt/common.py
index a85d955..57fea45 100644
--- a/python/invirt/common.py
+++ b/python/invirt/common.py
@@ -3,28 +3,35 @@ from __future__ import with_statement
 import unittest
 from fcntl import flock, LOCK_EX, LOCK_SH, LOCK_UN
 import contextlib as clib
+import subprocess
 
 class InvirtConfigError(AttributeError):
     pass
 
-class struct(object):
+class struct(dict):
     'A simple namespace object.'
-    def __init__(self, d = {}, __prefix = None, **kwargs):
-        'd is the dictionary or the items-iterable to update my __dict__ with.'
-        self.__dict__.update(d)
-        self.__dict__.update(kwargs)
+    def __init__(self, d = {}, __prefix = None, __default=None, **kwargs):
+        super(struct, self).__init__(d)
         self.__prefix = __prefix
+        self.__default = __default
+        self.update(kwargs)
     def __getattr__(self, key):
-        # XX ideally these would point a frame higher on the stack.
-        prefix = self.__prefix
-        if prefix is not None:
-            raise InvirtConfigError('missing configuration variable %s%s'
-                                    % (prefix, key))
-        else:
-            raise AttributeError("anonymous struct has no member '%s'"
-                                 % (key,))
+        try:
+            return self[key]
+        except KeyError:
+            if self.__default is None:
+                # XX ideally these would point a frame higher on the stack.
+                prefix = self.__prefix
+                if prefix is not None:
+                    raise InvirtConfigError('missing configuration variable '
+                                            '%s%s' % (prefix, key))
+                else:
+                    raise AttributeError("anonymous struct has no member '%s'"
+                                         % (key,))
+            else:
+                return struct({}, '', self.__default)
 
-def dicts2struct(x, prefix = None):
+def dicts2struct(x, prefix = None, default = None):
     """
     Given a tree of lists/dicts, perform a deep traversal to transform all the
     dicts to structs.
@@ -34,13 +41,15 @@ def dicts2struct(x, prefix = None):
     else:
         def newprefix(k): return prefix
     if type(x) == dict:
-        return struct(((k, dicts2struct(v, newprefix(k)))
+        return struct(((k, dicts2struct(v, newprefix(k), default))
                        for k,v in x.iteritems()),
-                      prefix)
+                      prefix,
+                      default)
     elif type(x) == list:
-        return [dicts2struct(v, newprefix(i)) for i, v in enumerate(x)]
+        return [dicts2struct(v, newprefix(i), default)
+                for i, v in enumerate(x)]
     elif x is None:
-        return struct({}, prefix)
+        return struct({}, prefix, default)
     else:
         return x
 
@@ -57,6 +66,30 @@ def lock_file(path, exclusive = True):
         finally:
             flock(f, LOCK_UN)
 
+def captureOutput(popen_args, stdin_str=None, *args, **kwargs):
+    """Capture stdout from a command.
+
+    This method will proxy the arguments to subprocess.Popen. It
+    returns the output from the command if the call succeeded and
+    raises an exception if the process returns a non-0 value.
+
+    This is intended to be a variant on the subprocess.check_call
+    function that also allows you access to the output from the
+    command.
+    """
+    if 'stdin' not in kwargs:
+        kwargs['stdin'] = subprocess.PIPE
+    if 'stdout' not in kwargs:
+        kwargs['stdout'] = subprocess.PIPE
+    if 'stderr' not in kwargs:
+        kwargs['stderr'] = subprocess.PIPE
+    p = subprocess.Popen(popen_args, *args, **kwargs)
+    out, err = p.communicate(stdin_str)
+    if p.returncode:
+        raise subprocess.CalledProcessError(p.returncode, '%s, stdout: %s, stderr: %s' %
+                                            (popen_args, out, err))
+    return out
+
 #
 # Exceptions.
 #
@@ -94,6 +127,7 @@ class common_tests(unittest.TestCase):
         self.assertEqual(structs.dict.list,   dicts['dict']['list'])
         self.assertEqual(structs.list[0],     dicts['list'][0])
         self.assertEqual(structs.list[1].key, dicts['list'][1]['key'])
+        self.assertEqual(set(structs), set(['atom', 'dict', 'list']))
 
 if __name__ == '__main__':
     unittest.main()