Check that a filename is a basestring instance

Instead of only checking one or another type of string-like object that
we accept, let's be able to check both. Previously, we only checked if
the filename was an instance of the native str type which on Python 2
excluded unicode filenames and bytes-like filenames on Python 3.

Fixes #2411

requests/compat.py

@@ -99,7 +99,6 @@ if is_py2:
     basestring = basestring
     numeric_types = (int, long, float)
 
-
 elif is_py3:
     from urllib.parse import urlparse, urlunparse, urljoin, urlsplit, urlencode, quote, unquote, quote_plus, unquote_plus, urldefrag
     from urllib.request import parse_http_list, getproxies, proxy_bypass

requests/utils.py

@@ -25,7 +25,8 @@ from . import __version__
 from . import certs
 from .compat import parse_http_list as _parse_list_header
 from .compat import (quote, urlparse, bytes, str, OrderedDict, unquote, is_py2,
-                     builtin_str, getproxies, proxy_bypass, urlunparse)
+                     builtin_str, getproxies, proxy_bypass, urlunparse,
+                     basestring)
 from .cookies import RequestsCookieJar, cookiejar_from_dict
 from .structures import CaseInsensitiveDict
 from .exceptions import InvalidURL
@@ -115,7 +116,8 @@ def get_netrc_auth(url):
 def guess_filename(obj):
     """Tries to guess the filename of the given object."""
     name = getattr(obj, 'name', None)
-    if name and isinstance(name, builtin_str) and name[0] != '<' and name[-1] != '>':
+    if (name and isinstance(name, basestring) and name[0] != '<' and
+            name[-1] != '>'):
         return os.path.basename(name)
 
 

test_requests.py

@@ -1265,6 +1265,32 @@ class UtilsTestCase(unittest.TestCase):
             'http://localhost.localdomain:5000/v1.0/') == {}
         assert get_environ_proxies('http://www.requests.com/') != {}
 
+    def test_guess_filename_when_int(self):
+        from requests.utils import guess_filename
+        assert None is guess_filename(1)
+
+    def test_guess_filename_when_filename_is_an_int(self):
+        from requests.utils import guess_filename
+        fake = type('Fake', (object,), {'name': 1})()
+        assert None is guess_filename(fake)
+
+    def test_guess_filename_with_file_like_obj(self):
+        from requests.utils import guess_filename
+        from requests import compat
+        fake = type('Fake', (object,), {'name': b'value'})()
+        guessed_name = guess_filename(fake)
+        assert b'value' == guessed_name
+        assert isinstance(guessed_name, compat.bytes)
+
+    def test_guess_filename_with_unicode_name(self):
+        from requests.utils import guess_filename
+        from requests import compat
+        filename = b'value'.decode('utf-8')
+        fake = type('Fake', (object,), {'name': filename})()
+        guessed_name = guess_filename(fake)
+        assert filename == guessed_name
+        assert isinstance(guessed_name, compat.str)
+
     def test_is_ipv4_address(self):
         from requests.utils import is_ipv4_address
         assert is_ipv4_address('8.8.8.8')