Add a SQL agent for interacting with SQL Databases and JSON Agent for interacting with large JSON blobs (#1150)

This PR adds 

* `ZeroShotAgent.as_sql_agent`, which returns an agent for interacting
with a sql database. This builds off of `SQLDatabaseChain`. The main
advantages are 1) answering general questions about the db, 2) access to
a tool for double checking queries, and 3) recovering from errors
* `ZeroShotAgent.as_json_agent` which returns an agent for interacting
with json blobs.
* Several examples in notebooks

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

tests/unit_tests/test_python.py

@@ -9,11 +9,13 @@ def test_python_repl() -> None:
 
     # Run a simple initial command.
     repl.run("foo = 1")
-    assert repl._locals["foo"] == 1
+    assert repl.locals is not None
+    assert repl.locals["foo"] == 1
 
     # Now run a command that accesses `foo` to make sure it still has it.
     repl.run("bar = foo * 2")
-    assert repl._locals["bar"] == 2
+    assert repl.locals is not None
+    assert repl.locals["bar"] == 2
 
 
 def test_python_repl_no_previous_variables() -> None:
@@ -29,7 +31,8 @@ def test_python_repl_pass_in_locals() -> None:
     _locals = {"foo": 4}
     repl = PythonREPL(_locals=_locals)
     repl.run("bar = foo * 2")
-    assert repl._locals["bar"] == 8
+    assert repl.locals is not None
+    assert repl.locals["bar"] == 8
 
 
 def test_functionality() -> None:
@@ -38,3 +41,15 @@ def test_functionality() -> None:
     code = "print(1 + 1)"
     output = chain.run(code)
     assert output == "2\n"
+
+
+def test_function() -> None:
+    """Test correct functionality."""
+    chain = PythonREPL()
+    code = "def add(a, b): " "    return a + b"
+    output = chain.run(code)
+    assert output == ""
+
+    code = "print(add(1, 2))"
+    output = chain.run(code)
+    assert output == "3\n"