diff --git a/Lib/formatter.py b/Lib/formatter.py
index 75f4718..ccbbdf1 100644
--- a/Lib/formatter.py
+++ b/Lib/formatter.py
@@ -38,7 +38,7 @@
     """
 
     def __init__(self, writer=None):
-        if not writer:
+        if writer is None:
             writer = NullWriter()
         self.writer = writer
     def end_paragraph(self, blankline): pass
@@ -433,7 +433,7 @@
 def test(file = None):
     w = DumbWriter()
     f = AbstractFormatter(w)
-    if file:
+    if file is not None:
         fp = open(file)
     elif sys.argv[1:]:
         fp = open(sys.argv[1])
diff --git a/Lib/ftplib.py b/Lib/ftplib.py
index 21b9e52..4a3d884 100644
--- a/Lib/ftplib.py
+++ b/Lib/ftplib.py
@@ -659,7 +659,7 @@
     __defacct = None
 
     def __init__(self, filename=None):
-        if not filename:
+        if filename is None:
             if os.environ.has_key("HOME"):
                 filename = os.path.join(os.environ["HOME"],
                                         ".netrc")
diff --git a/Lib/gettext.py b/Lib/gettext.py
index 0bea9ed..253b6d8 100644
--- a/Lib/gettext.py
+++ b/Lib/gettext.py
@@ -104,7 +104,7 @@
         self._info = {}
         self._charset = None
         self._fallback = None
-        if fp:
+        if fp is not None:
             self._parse(fp)
 
     def _parse(self, fp):
diff --git a/Lib/hmac.py b/Lib/hmac.py
index c9e4ae8..ba0a63c 100644
--- a/Lib/hmac.py
+++ b/Lib/hmac.py
@@ -46,7 +46,7 @@
         key = key + chr(0) * (blocksize - len(key))
         self.outer.update(_strxor(key, opad))
         self.inner.update(_strxor(key, ipad))
-        if (msg):
+        if msg is not None:
             self.update(msg)
 
 ##    def clear(self):