Issue #4756: zipfile.is_zipfile() now supports file-like objects.

Patch by Gabriel Genellina.

2 files changed, 53 insertions, 12 deletions

diff --git a/Lib/test/test_zipfile.py b/Lib/test/test_zipfile.py
index 5e99382..9cc5860 100644
--- a/Lib/test/test_zipfile.py
+++ b/Lib/test/test_zipfile.py
@@ -634,20 +634,49 @@ class OtherTests(unittest.TestCase):
     def testIsZipErroneousFile(self):
         # This test checks that the is_zipfile function correctly identifies
         # a file that is not a zip file
-        fp = open(TESTFN, "w")
-        fp.write("this is not a legal zip file\n")
-        fp.close()
+
+        # - passing a filename
+        with open(TESTFN, "w") as fp:
+            fp.write("this is not a legal zip file\n")
         chk = zipfile.is_zipfile(TESTFN)
-        self.assert_(chk is False)
+        self.assert_(not chk)
+        # - passing a file object
+        with open(TESTFN, "rb") as fp:
+            chk = zipfile.is_zipfile(fp)
+            self.assert_(not chk)
+        # - passing a file-like object
+        fp = StringIO()
+        fp.write("this is not a legal zip file\n")
+        chk = zipfile.is_zipfile(fp)
+        self.assert_(not chk)
+        fp.seek(0,0)
+        chk = zipfile.is_zipfile(fp)
+        self.assert_(not chk)
 
     def testIsZipValidFile(self):
         # This test checks that the is_zipfile function correctly identifies
         # a file that is a zip file
+
+        # - passing a filename
         zipf = zipfile.ZipFile(TESTFN, mode="w")
         zipf.writestr("foo.txt", "O, for a Muse of Fire!")
         zipf.close()
         chk = zipfile.is_zipfile(TESTFN)
-        self.assert_(chk is True)
+        self.assert_(chk)
+        # - passing a file object
+        with open(TESTFN, "rb") as fp:
+            chk = zipfile.is_zipfile(fp)
+            self.assert_(chk)
+            fp.seek(0,0)
+            zip_contents = fp.read()
+        # - passing a file-like object
+        fp = StringIO()
+        fp.write(zip_contents)
+        chk = zipfile.is_zipfile(fp)
+        self.assert_(chk)
+        fp.seek(0,0)
+        chk = zipfile.is_zipfile(fp)
+        self.assert_(chk)
 
     def testNonExistentFileRaisesIOError(self):
         # make sure we don't raise an AttributeError when a partially-constructed
diff --git a/Lib/zipfile.py b/Lib/zipfile.py
index bb8fc53..66fe078 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -128,18 +128,30 @@ _CD64_NUMBER_ENTRIES_TOTAL = 7
 _CD64_DIRECTORY_SIZE = 8
 _CD64_OFFSET_START_CENTDIR = 9
 
-def is_zipfile(filename):
-    """Quickly see if file is a ZIP file by checking the magic number."""
+def _check_zipfile(fp):
     try:
-        fpin = open(filename, "rb")
-        endrec = _EndRecData(fpin)
-        fpin.close()
-        if endrec:
-            return True                 # file has correct magic number
+        if _EndRecData(fp):
+            return True         # file has correct magic number
     except IOError:
         pass
     return False
 
+def is_zipfile(filename):
+    """Quickly see if a file is a ZIP file by checking the magic number.
+
+    The filename argument may be a file or file-like object too.
+    """
+    result = False
+    try:
+        if hasattr(filename, "read"):
+            result = _check_zipfile(fp=filename)
+        else:
+            with open(filename, "rb") as fp:
+                result = _check_zipfile(fp)
+    except IOError:
+        pass
+    return result
+
 def _EndRecData64(fpin, offset, endrec):
     """
     Read the ZIP64 end-of-archive records and use that to update endrec