bpo-29435: Allow is_tarfile to take a filelike obj

Author: woodruffw

Lib/tarfile.py

@@ -2461,9 +2461,14 @@ def __exit__(self, type, value, traceback):
 def is_tarfile(name):
     """Return True if name points to a tar archive that we
        are able to handle, else return False.
+
+       The name argument may be a file or file-like object.
     """
     try:
-        t = open(name)
+        if hasattr(name, "read"):
+            t = open(fileobj=name)
+        else:
+            t = open(name)
         t.close()
         return True
     except TarError:

Misc/NEWS.d/next/Library/2020-01-20-18-48-00.bpo-29435.qqJ2Ax.rst

@@ -0,0 +1,2 @@
+Allow :func:`tarfile.is_tarfile` to be used with file and file-like
+objects, like :func:`zipfile.is_zipfile`. Patch by William Woodruff.