bpo-32110: codecs.StreamReader.read(n) now returns not more than n (#4499)

characters/bytes for non-negative n.  This makes it compatible with
read() methods of other file-like objects.

1 files changed, 5 insertions, 3 deletions

diff --git a/Lib/codecs.py b/Lib/codecs.py
index 44618cbd2c..a70ed20f2b 100644
--- a/Lib/codecs.py
+++ b/Lib/codecs.py
@@ -480,15 +480,17 @@ class StreamReader(Codec):
             self.charbuffer = self._empty_charbuffer.join(self.linebuffer)
             self.linebuffer = None
 
+        if chars < 0:
+            # For compatibility with other read() methods that take a
+            # single argument
+            chars = size
+
         # read until we get the required number of characters (if available)
         while True:
             # can the request be satisfied from the character buffer?
             if chars >= 0:
                 if len(self.charbuffer) >= chars:
                     break
-            elif size >= 0:
-                if len(self.charbuffer) >= size:
-                    break
             # we need more data
             if size < 0:
                 newdata = self.stream.read()