improve the command-line interface of json.tool (closes #21000)

A patch from Berker Peksag.

2 files changed, 23 insertions, 12 deletions

diff --git a/Lib/json/tool.py b/Lib/json/tool.py
index 7db4528..cd57e4f 100644
--- a/Lib/json/tool.py
+++ b/Lib/json/tool.py
@@ -10,21 +10,24 @@ Usage::
     Expecting property name enclosed in double quotes: line 1 column 3 (char 2)
 
 """
-import sys
+import argparse
 import json
+import sys
+
 
 def main():
-    if len(sys.argv) == 1:
-        infile = sys.stdin
-        outfile = sys.stdout
-    elif len(sys.argv) == 2:
-        infile = open(sys.argv[1], 'r')
-        outfile = sys.stdout
-    elif len(sys.argv) == 3:
-        infile = open(sys.argv[1], 'r')
-        outfile = open(sys.argv[2], 'w')
-    else:
-        raise SystemExit(sys.argv[0] + " [infile [outfile]]")
+    prog = 'python -m json.tool'
+    description = ('A simple command line interface for json module '
+                   'to validate and pretty-print JSON objects.')
+    parser = argparse.ArgumentParser(prog=prog, description=description)
+    parser.add_argument('infile', nargs='?', type=argparse.FileType(),
+                        help='a JSON file to be validated or pretty-printed')
+    parser.add_argument('outfile', nargs='?', type=argparse.FileType('w'),
+                        help='write the output of infile to outfile')
+    options = parser.parse_args()
+
+    infile = options.infile or sys.stdin
+    outfile = options.outfile or sys.stdout
     with infile:
         try:
             obj = json.load(infile)
diff --git a/Lib/test/test_json/test_tool.py b/Lib/test/test_json/test_tool.py
index 0c39e56..5484a8a 100644
--- a/Lib/test/test_json/test_tool.py
+++ b/Lib/test/test_json/test_tool.py
@@ -55,6 +55,7 @@ class TestTool(unittest.TestCase):
     def test_infile_stdout(self):
         infile = self._create_infile()
         rc, out, err = assert_python_ok('-m', 'json.tool', infile)
+        self.assertEqual(rc, 0)
         self.assertEqual(out.splitlines(), self.expect.encode().splitlines())
         self.assertEqual(err, b'')
 
@@ -65,5 +66,12 @@ class TestTool(unittest.TestCase):
         self.addCleanup(os.remove, outfile)
         with open(outfile, "r") as fp:
             self.assertEqual(fp.read(), self.expect)
+        self.assertEqual(rc, 0)
         self.assertEqual(out, b'')
         self.assertEqual(err, b'')
+
+    def test_help_flag(self):
+        rc, out, err = assert_python_ok('-m', 'json.tool', '-h')
+        self.assertEqual(rc, 0)
+        self.assertTrue(out.startswith(b'usage: '))
+        self.assertEqual(err, b'')