python · samtatasurya · Nov 6, 2019 · Nov 9, 2019 · Nov 6, 2019 · Nov 9, 2019
diff --git a/Lib/lib2to3/fixer_util.py b/Lib/lib2to3/fixer_util.py
@@ -150,6 +150,38 @@ def ImportAndCall(node, results, names):
     new.prefix = node.prefix
     return new
 
+def BlankLineOrPass(node):
+    """Returns either a blank line or a pass statement depending on
+    the node's parent's siblings to maintain syntactic correctness
+    within a suite after conversion"""
+    skip = {token.NEWLINE, token.INDENT, token.DEDENT}
+    def has_significant_sibling(node, is_forward):
+        if is_forward:
+            sibling = node.next_sibling
+        else:
+            sibling = node.prev_sibling
+        while sibling:
+            if isinstance(sibling, Node):
+                if sibling.type != syms.simple_stmt:
+                    return True
+                for child in sibling.children:
+                    if child.type not in skip:
+                        return True
+            elif isinstance(sibling, Leaf) and sibling.type not in skip:
+                return True
+            if is_forward:
+                sibling = sibling.next_sibling
+            else:
+                sibling = sibling.prev_sibling
+        return False
+
+    parent = node.parent
+    if parent and parent.parent and parent.parent.type == syms.suite:
+        if (not has_significant_sibling(parent, False)
+            and not has_significant_sibling(parent, True)):
+            return Name("pass")
+    return BlankLine()
+
 
 ###########################################################
 ### Determine whether a node represents a given literal

diff --git a/Lib/lib2to3/fixes/fix_future.py b/Lib/lib2to3/fixes/fix_future.py
@@ -6,7 +6,7 @@
 
 # Local imports
 from .. import fixer_base
-from ..fixer_util import BlankLine
+from ..fixer_util import BlankLineOrPass
 
 class FixFuture(fixer_base.BaseFix):
     BM_compatible = True
@@ -17,6 +17,6 @@ class FixFuture(fixer_base.BaseFix):
     run_order = 10
 
     def transform(self, node, results):
-        new = BlankLine()
+        new = BlankLineOrPass(node)
         new.prefix = node.prefix
         return new
@@ -2,7 +2,7 @@
 
 # Local imports
 from lib2to3 import fixer_base
-from lib2to3.fixer_util import BlankLine, syms, token
+from lib2to3.fixer_util import BlankLineOrPass, syms, token
 
 
 class FixItertoolsImports(fixer_base.BaseFix):
@@ -52,6 +52,6 @@ def transform(self, node, results):
         if (not (imports.children or getattr(imports, 'value', None)) or
             imports.parent is None):
             p = node.prefix
-            node = BlankLine()
+            node = BlankLineOrPass(node)
             node.prefix = p
             return node
diff --git a/Lib/lib2to3/tests/test_fixers.py b/Lib/lib2to3/tests/test_fixers.py
@@ -25,15 +25,16 @@ def setUp(self, fix_list=None, fixer_pkg="lib2to3", options=None):
                            self.refactor.post_order):
             fixer.log = self.fixer_log
 
-    def _check(self, before, after):
-        before = support.reformat(before)
-        after = support.reformat(after)
+    def _check(self, before, after, reformat=True):
+        if reformat:
+            before = support.reformat(before)
+            after = support.reformat(after)
         tree = self.refactor.refactor_string(before, self.filename)
         self.assertEqual(after, str(tree))
         return tree
 
-    def check(self, before, after, ignore_warnings=False):
-        tree = self._check(before, after)
+    def check(self, before, after, ignore_warnings=False, reformat=True):
+        tree = self._check(before, after, reformat=reformat)
         self.assertTrue(tree.was_changed)
         if not ignore_warnings:
             self.assertEqual(self.fixer_log, [])
@@ -3656,9 +3657,130 @@ def test_future(self):
         a = """\n# comment"""
         self.check(b, a)
 
+    def test_suite_try_blank(self):
+        b = (
+        "try:\n"
+        "    from __future__ import with_statement\n"
+        "    from sys import exit\n"
+        "except ImportError:\n"
+        "    pass\n")
+        a =  (
+        "try:\n"
+        "    \n"
+        "    from sys import exit\n"
+        "except ImportError:\n"
+        "    pass\n")
+        self.check(b, a, reformat=False)  # to avoid dedent
+
+    def test_suite_try_pass(self):
+        b = (
+        "try:\n"
+        "    from __future__ import with_statement\n"
+        "except ImportError:\n"
+        "    pass\n")
+        a =  (
+        "try:\n"
+        "    pass\n"
+        "except ImportError:\n"
+        "    pass\n")
+        self.check(b, a)
+
+    def test_suite_if_blank(self):
+        b = (
+        "if sys.version_info < (3, 0):\n"
+        "    from __future__ import with_statement\n"
+        "    from sys import exit\n")
+        a = (
+        "if sys.version_info < (3, 0):\n"
+        "    \n"
+        "    from sys import exit\n")
+        self.check(b, a, reformat=False)  # to avoid dedent
+
+    def test_suite_if_pass(self):
+        b = (
+        "if sys.version_info < (3, 0):\n"
+        "    from __future__ import with_statement\n")
+        a = (
+        "if sys.version_info < (3, 0):\n"
+        "    pass\n")
+        self.check(b, a)  # to avoid dedent
+
+    def test_pass_with_comments(self):
+        b = (
+        "try:\n"
+        "    # this comment\n"
+        "    from __future__ import with_statement  # that comment\n"
+        "except ImportError:\n"
+        "    pass\n")
+        a = (
+        "try:\n"
+        "    # this comment\n"
+        "    pass  # that comment\n"
+        "except ImportError:\n"
+        "    pass\n")
+        self.check(b, a)
+
+    def test_pass_with_newlines(self):
+        b = (
+        "try:\n"
+        "    \n"
+        "    \n"
+        "    from __future__ import with_statement\n"
+        "    \n"
+        "except ImportError:\n"
+        "    pass\n")
+        a = (
+        "try:\n"
+        "    \n"
+        "    \n"
+        "    pass\n"
+        "    \n"
+        "except ImportError:\n"
+        "    pass\n")
+        self.check(b, a)
+
     def test_run_order(self):
         self.assert_runs_after('print')
 
+
+class Test_future_with_itertools_imports(FixerTestCase):
+
+    def setUp(self):
+        fix_list = ["future", "itertools_imports"]
+        super(Test_future_with_itertools_imports, self).setUp(fix_list)
+
+    def test_double_transform(self):
+        """Note the difference between the two conversion results, due to
+        the fact that 'future' fixer runs last"""
+        b = (
+        "try:\n"
+        "    from __future__ import with_statement\n"
+        "    from itertools import imap\n"
+        "except ImportError:\n"
+        "    pass\n")
+        a = (
+        "try:\n"
+        "    pass\n"
+        "    \n"
+        "except ImportError:\n"
+        "    pass\n")
+        self.check(b, a, reformat=False)  # to avoid dedent
+
+        b = (
+        "try:\n"
+        "    from itertools import imap\n"
+        "    from __future__ import with_statement\n"
+        "except ImportError:\n"
+        "    pass\n")
+        a = (
+        "try:\n"
+        "    \n"
+        "    pass\n"
+        "except ImportError:\n"
+        "    pass\n")
+        self.check(b, a, reformat=False)  # to avoid dedent
+
+
 class Test_itertools(FixerTestCase):
     fixer = "itertools"
 
@@ -3784,11 +3906,92 @@ def test_ifilter_and_zip_longest(self):
             a = "from itertools import bar, %s, foo" % (name,)
             self.check(b, a)
 
+    def test_suite_try_blank(self):
+        b = (
+        "try:\n"
+        "    from itertools import imap\n"
+        "    from sys import exit\n"
+        "except ImportError:\n"
+        "    pass\n")
+        a =  (
+        "try:\n"
+        "    \n"
+        "    from sys import exit\n"
+        "except ImportError:\n"
+        "    pass\n")
+        self.check(b, a, reformat=False)  # to avoid dedent
+
+    def test_suite_try_pass(self):
+        b = (
+        "try:\n"
+        "    from itertools import imap\n"
+        "except ImportError:\n"
+        "    pass\n")
+        a =  (
+        "try:\n"
+        "    pass\n"
+        "except ImportError:\n"
+        "    pass\n")
+        self.check(b, a)
+
+    def test_suite_if_blank(self):
+        b = (
+        "if sys.version_info < (3, 0):\n"
+        "    from itertools import imap\n"
+        "    from sys import exit\n")
+        a = (
+        "if sys.version_info < (3, 0):\n"
+        "    \n"
+        "    from sys import exit\n")
+        self.check(b, a, reformat=False)  # to avoid dedent
+
+    def test_suite_if_pass(self):
+        b = (
+        "if sys.version_info < (3, 0):\n"
+        "    from itertools import imap\n")
+        a = (
+        "if sys.version_info < (3, 0):\n"
+        "    pass\n")
+        self.check(b, a)  # to avoid dedent
+
+    def test_pass_with_comments(self):
+        b = (
+        "try:\n"
+        "    # this comment\n"
+        "    from itertools import imap  # that comment\n"
+        "except ImportError:\n"
+        "    pass\n")
+        a = (
+        "try:\n"
+        "    # this comment\n"
+        "    pass  # that comment\n"
+        "except ImportError:\n"
+        "    pass\n")
+        self.check(b, a)
+
+    def test_pass_with_newlines(self):
+        b = (
+        "try:\n"
+        "    \n"
+        "    \n"
+        "    from itertools import imap\n"
+        "    \n"
+        "except ImportError:\n"
+        "    pass\n")
+        a = (
+        "try:\n"
+        "    \n"
+        "    \n"
+        "    pass\n"
+        "    \n"
+        "except ImportError:\n"
+        "    pass\n")
+        self.check(b, a)
+
     def test_import_star(self):
         s = "from itertools import *"
         self.unchanged(s)
 
-
     def test_unchanged(self):
         s = "from itertools import foo"
         self.unchanged(s)

diff --git a/Misc/NEWS.d/next/Library/2019-11-09-06-16-24.bpo-38681.jJobMS.rst b/Misc/NEWS.d/next/Library/2019-11-09-06-16-24.bpo-38681.jJobMS.rst
@@ -0,0 +1,2 @@
+Transformation performed by certain fixers (e.g. future, itertools_imports) that causes a statement to be replaced by a blank line will generate a Python file that contains a syntax error. Enhancement applied checks whether the statement to be replaced has any siblings or not. If no sibling is found, then the statement gets replaced with a "pass" statement instead of a blank line.
+By doing this, Python source files generated by 2to3 are more readily runnable right after the transformation.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Transformation performed by certain fixers (e.g. future, itertools_imports) that causes a statement to be replaced by a blank line will generate a Python file that contains a syntax error. Enhancement applied checks whether the statement to be replaced has any siblings or not. If no sibling is found, then the statement gets replaced with a "pass" statement instead of a blank line.
		By doing this, Python source files generated by 2to3 are more readily runnable right after the transformation.