Support requirements on standard input

Allow a --file parameter of "-" to indicate the package list is read
on standard input, to support use in a traditional command pipeline.

Change-Id: Ic6e54af185e4b07825fcde3ef991f53de0a9ecfa

README.rst

@@ -18,6 +18,10 @@ dependencies. Users without `bindep` installed can consult the
 ``other-requirements.txt`` file by hand if they choose, or install `bindep`
 first and then use it.
 
+If you need to maintain multiple requirements list files you can pass a
+specific filename with the -f/--file command line option. If you want to read
+the list from standard input in a pipeline instead, use a filename of "-".
+
 Profiles
 --------
 

bindep/main.py

@@ -40,12 +40,15 @@ def main(depends=None):
         help="List the platform and configuration profiles.")
     opts, args = parser.parse_args()
     if depends is None:
-        try:
-            content = open(opts.filename, 'rt').read()
-        except IOError:
-            logging.error('No %s file found.' % opts.filename)
-            return 1
-        depends = bindep.depends.Depends(content)
+        if opts.filename == "-":
+            fd = sys.stdin
+        else:
+            try:
+                fd = open(opts.filename, 'rt')
+            except IOError:
+                logging.error('No %s file found.' % opts.filename)
+                return 1
+        depends = bindep.depends.Depends(fd.read())
     if opts.profiles:
         logging.info("Platform profiles:")
         for profile in depends.platform_profiles():

bindep/tests/test_main.py

@@ -100,6 +100,12 @@ class TestMain(TestCase):
             'No alternative-requirements.txt file found.\n',
             fixture.logger.output)
 
+    def test_stdin_requirements_file(self):
+        fixture = self.useFixture(MainFixture())
+        self.useFixture(MonkeyPatch('sys.argv', ['bindep', '--file', '-']))
+        self.assertEqual(0, main())
+        self.assertEqual('', fixture.logger.output)
+
     def test_specific_profile(self):
         logger = self.useFixture(FakeLogger())
         self.useFixture(MonkeyPatch('sys.argv', ['bindep', 'myprofile']))