diff --git a/.gitignore b/.gitignore
index ab599fc..d90d325 100644
--- a/.gitignore
+++ b/.gitignore
@@ -22,3 +22,4 @@ dist
 
 .coverage
 .cover/*
+/.venv/
diff --git a/prettytable/__init__.py b/prettytable/__init__.py
index bef5807..0b24e56 100644
--- a/prettytable/__init__.py
+++ b/prettytable/__init__.py
@@ -34,4 +34,4 @@
 
 from .prettytable import PrettyTable
 from .prettytable import ALL, HEADER, MSWORD_FRIENDLY, NONE, PLAIN_COLUMNS
-from .factory import from_csv, from_db_cursor, from_html, from_html_one
+from .factory import from_csv, from_json, from_db_cursor, from_html, from_html_one
diff --git a/prettytable/factory.py b/prettytable/factory.py
index 9e7d742..b8611d9 100644
--- a/prettytable/factory.py
+++ b/prettytable/factory.py
@@ -2,6 +2,7 @@
 Table factories
 """
 import csv
+import json
 from .prettytable import PrettyTable
 from ._compact import py3k, HTMLParser
 
@@ -34,6 +35,28 @@ def from_csv(fp, field_names=None, **kwargs):
     return table
 
 
+def from_json(fp, field_names=None, **kwargs):
+    reader = json.load(fp)
+
+    table = PrettyTable(**kwargs)
+    table_field_names = []
+    if field_names:
+        table_field_names.extend(field_names)
+    else:
+        for row in reader:
+            table_field_names.extend([x for x in row.keys() if x not in table_field_names])
+
+    table.field_names = table_field_names
+
+    for row in reader:
+        d = {k: "" for k in table_field_names}
+        d.update(row)
+        add_row = [x for x in d.values()]
+        table.add_row(add_row)
+
+    return table
+
+
 def from_db_cursor(cursor, **kwargs):
     if cursor.description:
         table = PrettyTable(**kwargs)
diff --git a/prettytable/prettytable.py b/prettytable/prettytable.py
index 02dab66..e0e0f2d 100644
--- a/prettytable/prettytable.py
+++ b/prettytable/prettytable.py
@@ -421,7 +421,7 @@ def align(self):
     def align(self, val):
         if not self._field_names:
             self._align = {}
-        elif val is None or (isinstance(val, dict) and len(val) is 0):
+        elif val is None or (isinstance(val, dict) and len(val) == 0):
             for field in self._field_names:
                 self._align[field] = "c"
         else:
@@ -441,7 +441,7 @@ def valign(self):
     def valign(self, val):
         if not self._field_names:
             self._valign = {}
-        elif val is None or (isinstance(val, dict) and len(val) is 0):
+        elif val is None or (isinstance(val, dict) and len(val) == 0):
             for field in self._field_names:
                 self._valign[field] = "t"
         else:
@@ -459,7 +459,7 @@ def max_width(self):
 
     @max_width.setter
     def max_width(self, val):
-        if val is None or (isinstance(val, dict) and len(val) is 0):
+        if val is None or (isinstance(val, dict) and len(val) == 0):
             self._max_width = {}
         else:
             self._validate_option("max_width", val)
@@ -489,7 +489,7 @@ def min_width(self):
 
     @min_width.setter
     def min_width(self, val):
-        if val is None or (isinstance(val, dict) and len(val) is 0):
+        if val is None or (isinstance(val, dict) and len(val) == 0):
             self._min_width = {}
         else:
             self._validate_option("min_width", val)
@@ -687,7 +687,7 @@ def int_format(self):
 
     @int_format.setter
     def int_format(self, val):
-        if val is None or (isinstance(val, dict) and len(val) is 0):
+        if val is None or (isinstance(val, dict) and len(val) == 0):
             self._int_format = {}
         else:
             self._validate_option("int_format", val)
@@ -704,7 +704,7 @@ def float_format(self):
 
     @float_format.setter
     def float_format(self, val):
-        if val is None or (isinstance(val, dict) and len(val) is 0):
+        if val is None or (isinstance(val, dict) and len(val) == 0):
             self._float_format = {}
         else:
             self._validate_option("float_format", val)
@@ -1295,7 +1295,7 @@ def _stringify_header(self, options):
                 fieldname = field.lower()
             else:
                 fieldname = field
-            bits.append(" " * lpad + self._justify(fieldname, width, self._align[field]) + " " * rpad)
+            bits.append(" " * lpad + self._justify(fieldname, width, self._align.get(field, 'c')) + " " * rpad)
             if options["border"]:
                 if options["vrules"] == ALL:
                     bits.append(options["vertical_char"])
@@ -1343,7 +1343,7 @@ def _stringify_row(self, row, options):
 
         for field, value, width, in zip(self._field_names, row, self._widths):
 
-            valign = self._valign[field]
+            valign = self._valign.get(field, 'm')
             lines = value.split("\n")
             dHeight = row_height - len(lines)
             if dHeight:
@@ -1359,7 +1359,7 @@ def _stringify_row(self, row, options):
                 if options["fields"] and field not in options["fields"]:
                     continue
 
-                bits[y].append(" " * lpad + self._justify(l, width, self._align[field]) + " " * rpad)
+                bits[y].append(" " * lpad + self._justify(l, width, self._align.get(field, 'c')) + " " * rpad)
                 if options["border"]:
                     if options["vrules"] == ALL:
                         bits[y].append(self.vertical_char)
diff --git a/tests/test_prettytable.py b/tests/test_prettytable.py
index 064e2b0..05bd427 100644
--- a/tests/test_prettytable.py
+++ b/tests/test_prettytable.py
@@ -3,7 +3,7 @@
 
 from prettytable import PrettyTable
 from prettytable import ALL, HEADER, MSWORD_FRIENDLY, NONE
-from prettytable import from_csv, from_db_cursor, from_html, from_html_one
+from prettytable import from_csv, from_json, from_db_cursor, from_html, from_html_one
 
 from prettytable._compact import StringIO
 try:
@@ -64,29 +64,28 @@ def testRowMixEquivalenceHTML(self):
         self.assertEqual(self.row.get_html_string(), self.mix.get_html_string())
 
 
-# class FieldnamelessTableTest(unittest.TestCase):
-#
-#    """Make sure that building and stringing a table with no fieldnames works fine"""
-#
-#    def setUp(self):
-#        self.x = PrettyTable()
-#        self.x.add_row(["Adelaide",1295, 1158259, 600.5])
-#        self.x.add_row(["Brisbane",5905, 1857594, 1146.4])
-#        self.x.add_row(["Darwin", 112, 120900, 1714.7])
-#        self.x.add_row(["Hobart", 1357, 205556, 619.5])
-#        self.x.add_row(["Sydney", 2058, 4336374, 1214.8])
-#        self.x.add_row(["Melbourne", 1566, 3806092, 646.9])
-#        self.x.add_row(["Perth", 5386, 1554769, 869.4])
-#
-#    def testCanStringASCII(self):
-#        self.x.get_string()
-#
-#    def testCanStringHTML(self):
-#        self.x.get_html_string()
-#
-#    def testAddFieldnamesLater(self):
-#        self.x.field_names = ["City name", "Area", "Population", "Annual Rainfall"]
-#        self.x.get_string()
+class FieldnamelessTableTest(unittest.TestCase):
+    """Make sure that building and stringing a table with no fieldnames works fine"""
+
+    def setUp(self):
+        self.x = PrettyTable()
+        self.x.add_row(["Adelaide", 1295, 1158259, 600.5])
+        self.x.add_row(["Brisbane", 5905, 1857594, 1146.4])
+        self.x.add_row(["Darwin", 112, 120900, 1714.7])
+        self.x.add_row(["Hobart", 1357, 205556, 619.5])
+        self.x.add_row(["Sydney", 2058, 4336374, 1214.8])
+        self.x.add_row(["Melbourne", 1566, 3806092, 646.9])
+        self.x.add_row(["Perth", 5386, 1554769, 869.4])
+
+    def testCanStringASCII(self):
+        self.x.get_string()
+
+    def testCanStringHTML(self):
+        self.x.get_html_string()
+
+    def testAddFieldnamesLater(self):
+        self.x.field_names = ["City name", "Area", "Population", "Annual Rainfall"]
+        self.x.get_string()
 
 
 class CityDataTest(unittest.TestCase):
@@ -595,6 +594,59 @@ def setUp(self):
         self.x = from_csv(csv_fp)
 
 
+class JsonConstructorTest(BasicTests):
+    def setUp(self):
+        json_string = """[
+  {
+    "City name": "Sydney",
+    "Area": "2058",
+    "Population": "4336374",
+    "Annual Rainfall": "1214.8"
+  },
+  {
+    "City name": "Melbourne",
+    "Area": "1566",
+    "Population": "3806092",
+    "Annual Rainfall": "646.9"
+  },
+  {
+    "City name": "Brisbane",
+    "Area": "5905",
+    "Population": "1857594",
+    "Annual Rainfall": "1146.4"
+  },
+  {
+    "City name": "Perth",
+    "Area": "5386",
+    "Population": "1554769",
+    "Coordinates": "31.9523° S, 115.8613° E",
+    "Annual Rainfall": "869.4"
+  },
+  {
+    "City name": "Adelaide",
+    "Area": "1295",
+    "Population": "1158259",
+    "Annual Rainfall": "600.5"
+  },
+  {
+    "City name": "Hobart",
+    "Area": "1357",
+    "Population": "205556",
+    "Annual Rainfall": "619.5"
+  },
+  {
+    "City name": "Darwin",
+    "Area": "0112",
+    "Population": "120900",
+    "Annual Rainfall": "1714.7"
+  }
+]"""
+        json_fp = StringIO.StringIO(json_string)
+        self.x = from_json(json_fp)
+        print("Generated using json:")
+        print(self.x)
+
+
 if _have_sqlite:
     class DatabaseConstructorTest(BasicTests):
         def setUp(self):