Add file args to input builtin.

This is a change to add support for overriding input, output, and error
files used by the input builtin.

See https://bugs.python.org/issue31603 for more.

Author: Wren Turkal

Lib/test/test_builtin.py

@@ -1628,6 +1628,23 @@ def child(wpipe):
         )
         self.assertSequenceEqual(lines, expected)
 
+    def test_input_override_stdin(self):
+        input_buf = io.StringIO('quux\n')
+        input_received = input(infile=input_buf)
+        self.assertSequenceEqual('quux', input_received)
+
+    def test_input_override_stdout(self):
+        output_buf = io.StringIO()
+        input_buf = io.StringIO('\n')
+        input('blah: ', infile=input_buf, outfile=output_buf)
+        self.assertSequenceEqual('blah: ', output_buf.getvalue())
+
+    def test_input_override_stderr(self):
+        error_buf = io.StringIO()
+        input_buf = io.StringIO('\n')
+        self.assertRaises(RuntimeError, input, 'blah: ', infile=input_buf,
+                          outfile=None, errfile=error_buf)
+
 class TestSorted(unittest.TestCase):
 
     def test_basic(self):

Python/bltinmodule.c

@@ -1842,23 +1842,30 @@ input as builtin_input
 
     prompt: object(c_default="NULL") = None
     /
+    *
+    infile: object(c_default="_PySys_GetObjectId(&PyId_stdin)") = None
+    outfile: object(c_default="_PySys_GetObjectId(&PyId_stdout)") = None
+    errfile: object(c_default="_PySys_GetObjectId(&PyId_stderr)") = None
 
 Read a string from standard input.  The trailing newline is stripped.
 
 The prompt string, if given, is printed to standard output without a
 trailing newline before reading input.
+The defaults for infile, outfile, and errfile if they not provided are equivalent
+to sys.stdin, sys.stdout, and sys.stderr respectively.
 
 If the user hits EOF (*nix: Ctrl-D, Windows: Ctrl-Z+Return), raise EOFError.
 On *nix systems, readline is used if available.
 [clinic start generated code]*/
 
 static PyObject *
-builtin_input_impl(PyObject *module, PyObject *prompt)
-/*[clinic end generated code: output=83db5a191e7a0d60 input=5e8bb70c2908fe3c]*/
+builtin_input_impl(PyObject *module, PyObject *prompt, PyObject *infile,
+                   PyObject *outfile, PyObject *errfile)
+/*[clinic end generated code: output=40acdfd4ce9e4222 input=f7d6c671b75027bc]*/
 {
-    PyObject *fin = _PySys_GetObjectId(&PyId_stdin);
-    PyObject *fout = _PySys_GetObjectId(&PyId_stdout);
-    PyObject *ferr = _PySys_GetObjectId(&PyId_stderr);
+    PyObject *fin = infile;
+    PyObject *fout = outfile;
+    PyObject *ferr = errfile;
     PyObject *tmp;
     long fd;
     int tty;

Python/clinic/bltinmodule.c.h

@@ -528,35 +528,43 @@ builtin_pow(PyObject *module, PyObject **args, Py_ssize_t nargs)
 }
 
 PyDoc_STRVAR(builtin_input__doc__,
-"input($module, prompt=None, /)\n"
+"input($module, prompt=None, /, *, infile=None, outfile=None,\n"
+"      errfile=None)\n"
 "--\n"
 "\n"
 "Read a string from standard input.  The trailing newline is stripped.\n"
 "\n"
 "The prompt string, if given, is printed to standard output without a\n"
 "trailing newline before reading input.\n"
+"The defaults for infile, outfile, and errfile if they not provided are equivalent\n"
+"to sys.stdin, sys.stdout, and sys.stderr respectively.\n"
 "\n"
 "If the user hits EOF (*nix: Ctrl-D, Windows: Ctrl-Z+Return), raise EOFError.\n"
 "On *nix systems, readline is used if available.");
 
 #define BUILTIN_INPUT_METHODDEF    \
-    {"input", (PyCFunction)builtin_input, METH_FASTCALL, builtin_input__doc__},
+    {"input", (PyCFunction)builtin_input, METH_FASTCALL|METH_KEYWORDS, builtin_input__doc__},
 
 static PyObject *
-builtin_input_impl(PyObject *module, PyObject *prompt);
+builtin_input_impl(PyObject *module, PyObject *prompt, PyObject *infile,
+                   PyObject *outfile, PyObject *errfile);
 
 static PyObject *
-builtin_input(PyObject *module, PyObject **args, Py_ssize_t nargs)
+builtin_input(PyObject *module, PyObject **args, Py_ssize_t nargs, PyObject *kwnames)
 {
     PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"", "infile", "outfile", "errfile", NULL};
+    static _PyArg_Parser _parser = {"|O$OOO:input", _keywords, 0};
     PyObject *prompt = NULL;
+    PyObject *infile = _PySys_GetObjectId(&PyId_stdin);
+    PyObject *outfile = _PySys_GetObjectId(&PyId_stdout);
+    PyObject *errfile = _PySys_GetObjectId(&PyId_stderr);
 
-    if (!_PyArg_UnpackStack(args, nargs, "input",
-        0, 1,
-        &prompt)) {
+    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
+        &prompt, &infile, &outfile, &errfile)) {
         goto exit;
     }
-    return_value = builtin_input_impl(module, prompt);
+    return_value = builtin_input_impl(module, prompt, infile, outfile, errfile);
 
 exit:
     return return_value;
@@ -676,4 +684,4 @@ builtin_issubclass(PyObject *module, PyObject **args, Py_ssize_t nargs)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=09752daa8cdd6ec7 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=4ca8e7840e9e74f3 input=a9049054013a1b77]*/