Create Python library `seven` in lldbsuite.support

[zturner]

Summary

The purpose of this file is to fill in the gaps where six is lacking support for some operation that we need.

Initially this just provides a replacement for the commands module which is no longer present in Python 3.

[tfiala]

Just one question on the python 3 return code for non-exceptional exit.

packages/Python/lldbsuite/support/seven.py

12

Is it correct to assume a 0 return code here? Couldn't we have output and have a non-zero status return that ins't a call exception?

[zturner]

packages/Python/lldbsuite/support/seven.py

12

The documentation of check_output says this:

Run command with arguments and return its output as a byte string.

If the return code was non-zero it raises a CalledProcessError. The CalledProcessError object will have the return code in the returncode attribute and any output in the output attribute.

So I think it's correct. Might not hurt to have a comment to that effect though

[tfiala]

OK looks good then.

[tfiala]

I think this went in, right?

packages/Python/lldbsuite/support/seven.py

+import six
+
+if six.PY2:
+    import commands
+    get_command_output = commands.getoutput
+    get_command_status_output = commands.getstatusoutput
+
+else:
+    def get_command_status_output(command):
+        try:
+            import subprocess
+            return (0, subprocess.check_output(command, shell=True))
+        except subprocess.CalledProcessError as e:
+            return (e.returncode, e.output)
+
+    def get_command_output(command):
+        return get_command_status_output(command)[1]