Added a new option to the multiple-statement-per-line warning to allow

if statements with single-line bodies on the same line. The option is off
by default.

ChangeLog

@@ -5,6 +5,9 @@ ChangeLog for Pylint
     * Avoid false used-before-assignment for except handler defined
      identifier used on the same line (#111)
 
+    * Add a new option for the multi-statement warning to
+      allow single-line if statements.
+
     * Add 'bad-context-manager' error, checking that '__exit__'
       special method accepts the right number of arguments.
 

checkers/format.py

@@ -193,6 +193,10 @@ class FormatChecker(BaseTokenChecker):
                  'default': r'^\s*(# )?<?https?://\S+>?$',
                  'help': ('Regexp for a line that is allowed to be longer than '
                           'the limit.')}),
+               ('single-line-if-stmt',
+                 {'default': False, 'type' : 'yn', 'metavar' : '<y_or_n>',
+                  'help' : ('Allow the body of an if to be on the same '
+                            'line as the test if there is no else.')}),
                ('max-module-lines',
                 {'default' : 1000, 'type' : 'int', 'metavar' : '<int>',
                  'help': 'Maximum number of lines in a module'}
@@ -307,16 +311,19 @@ def visit_default(self, node):
         if prev_sibl is not None:
             prev_line = prev_sibl.fromlineno
         else:
-            prev_line = node.parent.statement().fromlineno
+            # The line on which a finally: occurs in a try/finally
+            # is not directly represented in the AST. We infer it
+            # by taking the last line of the body and adding 1, which
+            # should be the line of finally:
+            if (isinstance(node.parent, nodes.TryFinally)
+                and node in node.parent.finalbody):
+                prev_line = node.parent.body[0].tolineno + 1
+            else:
+                prev_line = node.parent.statement().fromlineno
         line = node.fromlineno
         assert line, node
         if prev_line == line and self._visited_lines.get(line) != 2:
-            # py2.5 try: except: finally:
-            if not (isinstance(node, nodes.TryExcept)
-                    and isinstance(node.parent, nodes.TryFinally)
-                    and node.fromlineno == node.parent.fromlineno):
-                self.add_message('C0321', node=node)
-                self._visited_lines[line] = 2
+            self._check_multi_statement_line(node, line)
             return
         if line in self._visited_lines:
             return
@@ -340,6 +347,23 @@ def visit_default(self, node):
             # FIXME: internal error !
             pass
 
+    def _check_multi_statement_line(self, node, line):
+        """Check for lines containing multiple statements."""
+        # Do not warn about multiple nested context managers
+        # in with statements.
+        if isinstance(node, nodes.With):
+            return
+        # For try... except... finally..., the two nodes
+        # appear to be on the same line due to how the AST is built.
+        if (isinstance(node, nodes.TryExcept) and
+            isinstance(node.parent, nodes.TryFinally)):
+            return
+        if (isinstance(node.parent, nodes.If) and not node.parent.orelse
+            and self.config.single_line_if_stmt):
+            return
+        self.add_message('C0321', node=node)
+        self._visited_lines[line] = 2
+
     @check_messages('W0333')
     def visit_backquote(self, node):
         self.add_message('W0333', node=node)

test/input/func_format.py

@@ -85,3 +85,24 @@ def hop(context):
 <img src="images/drapeau_vert.png" alt="Drapeau vert" />\
 <strong>%s</strong></td></tr>' % aaaa
 
+with open('a') as a, open('b') as b:
+    pass
+
+with open('a') as a, open('b') as b: pass  # multiple-statements
+
+# Well-formatted try-except-finally block.
+try:
+    pass
+except IOError, e:
+    print e
+finally:
+    pass
+
+try:
+    pass
+except IOError, e:
+    print e
+finally: pass  # multiple-statements
+
+# This is not allowed by the default configuration.
+if True: print False

test/messages/func_format.txt

@@ -29,3 +29,6 @@ C: 71:_gc_debug: Operator not preceded by a space
 C: 73:_gc_debug: Operator not preceded by a space
             ocount[obj.__class__]=1
                                  ^
+C: 91: More than one statement on a single line
+C:105: More than one statement on a single line
+C:108: More than one statement on a single line

test/test_format.py

@@ -21,10 +21,11 @@
 from os import linesep
 
 from logilab.common.testlib import TestCase, unittest_main
+from astroid import test_utils
 
 from pylint.checkers.format import *
 
-from pylint.testutils import TestReporter
+from pylint.testutils import TestReporter, CheckerTestCase, Message
 
 REPORTER = TestReporter()
 
@@ -164,5 +165,42 @@ def test_known_values_tqstring(self):
     def test_known_values_tastring(self):
         self.assertEqual(check_line("print '''<a='=')\n'''"), None)
 
+
+class MultiStatementLineTest(CheckerTestCase):
+  CHECKER_CLASS = FormatChecker
+
+  def testSingleLineIfStmts(self):
+      stmt = test_utils.extract_node("""
+      if True: pass  #@
+      """)
+      with self.assertAddsMessages(Message('C0321', node=stmt.body[0])):
+          self.checker.process_tokens([])
+          self.checker.visit_default(stmt.body[0])
+      self.checker.config.single_line_if_stmt = True
+      with self.assertNoMessages():
+          self.checker.process_tokens([])
+          self.checker.visit_default(stmt.body[0])
+      stmt = test_utils.extract_node("""
+      if True: pass  #@
+      else:
+        pass
+      """)
+      with self.assertAddsMessages(Message('C0321', node=stmt.body[0])):
+          self.checker.process_tokens([])
+          self.checker.visit_default(stmt.body[0])
+
+  def testTryExceptFinallyNoMultipleStatement(self):
+      tree = test_utils.extract_node("""
+      try:  #@
+        pass
+      except:
+        pass
+      finally:
+        pass""")
+      with self.assertNoMessages():
+          self.checker.process_tokens([])
+          self.checker.visit_default(tree.body[0])
+
+
 if __name__ == '__main__':
     unittest_main()