Fix fromjson() to support reading from stdin

Author: yaniv-aknin

petl/io/json.py

@@ -16,7 +16,7 @@
 from petl.util.base import data, Table, dicts as _dicts, iterpeek
 
 
-def fromjson(source, *args, **kwargs):
+def fromjson(source=None, *args, **kwargs):
     """
     Extract data from a JSON file. The file must contain a JSON array as
     the top level object, and each member of the array will be treated as a

petl/test/test_executable.py

@@ -8,3 +8,15 @@ def test_executable():
         petl 'fromcsv().cut("foo").head(1).tocsv()'
     """, shell=True, check=True, capture_output=True)
     assert result.stdout == b'foo\r\na\r\n'
+
+def test_json_stdin():
+    result = subprocess.run("""
+        echo '[{"foo": "a", "bar": "b"}]' |
+        petl 'fromjson().tocsv()'
+    """, shell=True, check=True, capture_output=True)
+    assert result.stdout == b'foo,bar\r\na,b\r\n'
+    result = subprocess.run("""
+        ( echo '{"foo": "a", "bar": "b"}' ; echo '{"foo": "c", "bar": "d"}' ) |
+        petl 'fromjson(lines=True).tocsv()'
+    """, shell=True, check=True, capture_output=True)
+    assert result.stdout == b'foo,bar\r\na,b\r\nc,d\r\n'