Fall back to sys.getdefaultencoding in auto_decode (#4430)

* Test auto_decode when getpreferredencoding is None

* Fall back to sys.getdefaultencoding in auto_decode

* Add a news file fragment for 4184

Author: dmtucker

news/4184.bugfix

@@ -0,0 +1 @@
+Fall back to sys.getdefaultencoding() if locale.getpreferredencoding() returns None in `pip.utils.encoding.auto_decode`.

pip/utils/encoding.py

@@ -1,6 +1,7 @@
 import codecs
 import locale
 import re
+import sys
 
 BOMS = [
     (codecs.BOM_UTF8, 'utf8'),
@@ -27,4 +28,6 @@ def auto_decode(data):
         if line[0:1] == b'#' and ENCODING_RE.search(line):
             encoding = ENCODING_RE.search(line).groups()[0].decode('ascii')
             return data.decode(encoding)
-    return data.decode(locale.getpreferredencoding(False))
+    return data.decode(
+        locale.getpreferredencoding(False) or sys.getdefaultencoding(),
+    )

tests/unit/test_utils.py

@@ -464,6 +464,16 @@ def test_auto_decode_pep263_headers(self):
         latin1_req = u'# coding=latin1\n# Pas trop de café'
         assert auto_decode(latin1_req.encode('latin1')) == latin1_req
 
+    def test_auto_decode_no_preferred_encoding(self):
+        om, em = Mock(), Mock()
+        om.return_value = 'ascii'
+        em.return_value = None
+        data = u'data'
+        with patch('sys.getdefaultencoding', om):
+            with patch('locale.getpreferredencoding', em):
+                ret = auto_decode(data.encode(sys.getdefaultencoding()))
+        assert ret == data
+
 
 class TestTempDirectory(object):