bpo-33563: Fileinput(bufsize=0) does not emit deprecation warning.

Lib/fileinput.py

@@ -80,7 +80,9 @@
 
 _state = None
 
-def input(files=None, inplace=False, backup="", bufsize=0,
+_sentinel = object()
+
+def input(files=None, inplace=False, backup="", bufsize=_sentinel,
           mode="r", openhook=None):
     """Return an instance of the FileInput class, which can be iterated.
 
@@ -91,7 +93,13 @@ def input(files=None, inplace=False, backup="", bufsize=0,
     global _state
     if _state and _state._file:
         raise RuntimeError("input() already active")
-    _state = FileInput(files, inplace, backup, bufsize, mode, openhook)
+    if bufsize is not _sentinel:
+        import warnings
+        warnings.warn('bufsize is deprecated and ignored since Python 3.6'
+                      ' and will be removed in 3.8',
+                      DeprecationWarning, stacklevel=2)
+
+    _state = FileInput(files, inplace, backup, mode=mode, openhook=openhook)
     return _state
 
 def close():
@@ -185,7 +193,7 @@ class FileInput:
     sequential order; random access and readline() cannot be mixed.
     """
 
-    def __init__(self, files=None, inplace=False, backup="", bufsize=0,
+    def __init__(self, files=None, inplace=False, backup="", bufsize=_sentinel,
                  mode="r", openhook=None):
         if isinstance(files, str):
             files = (files,)
@@ -201,9 +209,10 @@ def __init__(self, files=None, inplace=False, backup="", bufsize=0,
         self._files = files
         self._inplace = inplace
         self._backup = backup
-        if bufsize:
+        if bufsize is not _sentinel:
             import warnings
-            warnings.warn('bufsize is deprecated and ignored',
+            warnings.warn('bufsize is deprecated and ignored since Python 3.6'
+                          ' and will be removed in 3.8',
                           DeprecationWarning, stacklevel=2)
         self._savestdout = None
         self._output = None

Lib/test/test_fileinput.py

@@ -83,12 +83,13 @@ def close(self):
 class BufferSizesTests(BaseTests, unittest.TestCase):
     def test_buffer_sizes(self):
         # First, run the tests with default and teeny buffer size.
-        for round, bs in (0, 0), (1, 30):
+        from fileinput import _sentinel
+        for round, bs in (0, 0), (1, 30), (2, _sentinel):
             t1 = self.writeTmp(''.join("Line %s of file 1\n" % (i+1) for i in range(15)))
             t2 = self.writeTmp(''.join("Line %s of file 2\n" % (i+1) for i in range(10)))
             t3 = self.writeTmp(''.join("Line %s of file 3\n" % (i+1) for i in range(5)))
             t4 = self.writeTmp(''.join("Line %s of file 4\n" % (i+1) for i in range(1)))
-            if bs:
+            if bs is  not _sentinel:
                 with self.assertWarns(DeprecationWarning):
                     self.buffer_size_test(t1, t2, t3, t4, bs, round)
             else:
@@ -646,9 +647,10 @@ def do_test_call_input(self):
         openhook = object()
 
         # call fileinput.input() with different values for each argument
-        result = fileinput.input(files=files, inplace=inplace, backup=backup,
-                                 bufsize=bufsize,
-            mode=mode, openhook=openhook)
+        with self.assertWarns(DeprecationWarning):
+            result = fileinput.input(files=files, inplace=inplace, backup=backup,
+                                    bufsize=bufsize,
+                mode=mode, openhook=openhook)
 
         # ensure fileinput._state was set to the returned object
         self.assertIs(result, fileinput._state, "fileinput._state")
@@ -658,10 +660,13 @@ def do_test_call_input(self):
         self.assertIs(files, result.files, "files")
         self.assertIs(inplace, result.inplace, "inplace")
         self.assertIs(backup, result.backup, "backup")
-        self.assertIs(bufsize, result.bufsize, "bufsize")
         self.assertIs(mode, result.mode, "mode")
         self.assertIs(openhook, result.openhook, "openhook")
 
+        # FileInput(bufsize=..) is deprecated, check that fileinut.input will
+        # _not_ its value to the MockFileInput
+        self.assertIsNot(bufsize, result.bufsize, "bufsize")
+
 class Test_fileinput_close(BaseFileInputGlobalMethodsTest):
     """Unit tests for fileinput.close()"""
 

Misc/NEWS.d/next/Library/2018-05-17-14-47-55.bpo-33563.y5rVPT.rst

@@ -0,0 +1,2 @@
+Improve fileinput's DeprecationWarning and emit them when bufsize=0 is
+passed.