1 files changed, 8 insertions, 7 deletions
diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index aec7009fed..40d438c45c 100755
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -1405,10 +1405,11 @@ class TarFile(object):
            can be determined, `mode' is overridden by `fileobj's mode.
            `fileobj' is not closed, when TarFile is closed.
         """
-        if len(mode) > 1 or mode not in "raw":
+        modes = {"r": "rb", "a": "r+b", "w": "wb"}
+        if mode not in modes:
             raise ValueError("mode must be 'r', 'a' or 'w'")
         self.mode = mode
-        self._mode = {"r": "rb", "a": "r+b", "w": "wb"}[mode]
+        self._mode = modes[mode]
 
         if not fileobj:
             if self.mode == "a" and not os.path.exists(name):
@@ -1564,7 +1565,7 @@ class TarFile(object):
             filemode = filemode or "r"
             comptype = comptype or "tar"
 
-            if filemode not in "rw":
+            if filemode not in ("r", "w"):
                 raise ValueError("mode must be 'r' or 'w'")
 
             stream = _Stream(name, filemode, comptype, fileobj, bufsize)
@@ -1576,7 +1577,7 @@ class TarFile(object):
             t._extfileobj = False
             return t
 
-        elif mode in "aw":
+        elif mode in ("a", "w"):
             return cls.taropen(name, mode, fileobj, **kwargs)
 
         raise ValueError("undiscernible mode")
@@ -1585,7 +1586,7 @@ class TarFile(object):
     def taropen(cls, name, mode="r", fileobj=None, **kwargs):
         """Open uncompressed tar archive name for reading or writing.
         """
-        if len(mode) > 1 or mode not in "raw":
+        if mode not in ("r", "a", "w"):
             raise ValueError("mode must be 'r', 'a' or 'w'")
         return cls(name, mode, fileobj, **kwargs)
 
@@ -1594,7 +1595,7 @@ class TarFile(object):
         """Open gzip compressed tar archive name for reading or writing.
            Appending is not allowed.
         """
-        if len(mode) > 1 or mode not in "rw":
+        if mode not in ("r", "w"):
             raise ValueError("mode must be 'r' or 'w'")
 
         try:
@@ -1625,7 +1626,7 @@ class TarFile(object):
         """Open bzip2 compressed tar archive name for reading or writing.
            Appending is not allowed.
         """
-        if len(mode) > 1 or mode not in "rw":
+        if mode not in ("r", "w"):
             raise ValueError("mode must be 'r' or 'w'.")
 
         try: