pythongh-87901: os.popen: Make encoding keyword only

Author: methane

Doc/library/os.rst

@@ -3916,7 +3916,7 @@ written in Python, such as a mail server's external command delivery program.
    .. availability:: Unix.
 
 
-.. function:: popen(cmd, mode='r', buffering=-1, encoding=None)
+.. function:: popen(cmd, mode='r', buffering=-1, *, encoding=None)
 
    Open a pipe to or from command *cmd*.
    The return value is an open file object

Lib/os.py

@@ -974,7 +974,7 @@ def spawnlpe(mode, file, *args):
 # command in a shell can't be supported.
 if sys.platform != 'vxworks':
     # Supply os.popen()
-    def popen(cmd, mode="r", buffering=-1, encoding=None):
+    def popen(cmd, mode="r", buffering=-1, *, encoding=None):
         if not isinstance(cmd, str):
             raise TypeError("invalid cmd type (%s, expected string)" % type(cmd))
         if mode not in ("r", "w"):