Apply suggestions from code review

Co-authored-by: Bénédikt Tran <[email protected]>

Author: yihong0618

Lib/base64.py

@@ -602,13 +602,10 @@ def main():
             func(f, sys.stdout.buffer)
     else:
         if sys.stdin.isatty():
-            # gh-gh-138775: read input data at once when reading from stdin
-            # This allows proper handling of EOF (Ctrl+D)
-            input_data = sys.stdin.buffer.read()
-            if input_data:
-                import io
-                input_buffer = io.BytesIO(input_data)
-                func(input_buffer, sys.stdout.buffer)
+            # gh-138775: read input data at once when reading from stdin.
+            import io
+            data = sys.stdin.buffer.read()
+            func(io.BytesIO(data), sys.stdout.buffer)
         else:
             # keep the old behaviour for non-interactive input
             func(sys.stdin.buffer, sys.stdout.buffer)

Misc/NEWS.d/next/Library/2025-09-11-15-03-37.gh-issue-138775.w7rnSx.rst

@@ -1 +1 @@
-Fix: handle "python -m base64" stdin correct with EOF single.
+:mod:`base64`: fix reading from stdin for the command-line interface.