MAINT: Clean up code

Fix small issues identified by ruff
Improve typing

Author: bashtage

examples/iv_basic-examples.ipynb

@@ -32,9 +32,11 @@
    "outputs": [],
    "source": [
     "import numpy as np\n",
-    "from linearmodels.datasets import mroz\n",
+    "import pandas as pd\n",
     "from statsmodels.api import add_constant\n",
     "\n",
+    "from linearmodels.datasets import mroz\n",
+    "\n",
     "print(mroz.DESCR)\n",
     "data = mroz.load()\n",
     "data = data.dropna()\n",
@@ -573,7 +575,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "import pandas as pd\n",
+    "v = IV2SLS(data[endog], data[exog + instr], None, None).fit().resids\n",
     "\n",
     "v = IV2SLS(data[endog], data[exog + instr], None, None).fit().resids\n",
     "\n",

examples/panel_examples.ipynb

@@ -29,6 +29,7 @@
    "outputs": [],
    "source": [
     "import pandas as pd\n",
+    "\n",
     "from linearmodels.datasets import wage_panel\n",
     "\n",
     "data = wage_panel.load()\n",
@@ -54,6 +55,7 @@
    "outputs": [],
    "source": [
     "import statsmodels.api as sm\n",
+    "\n",
     "from linearmodels.panel import PooledOLS\n",
     "\n",
     "exog_vars = [\"black\", \"hisp\", \"exper\", \"expersq\", \"married\", \"educ\", \"union\", \"year\"]\n",

examples/system_examples.ipynb

@@ -41,6 +41,7 @@
     "# Common libraries\n",
     "import numpy as np\n",
     "import pandas as pd\n",
+    "import seaborn as sns\n",
     "import statsmodels.api as sm"
    ]
   },
@@ -180,7 +181,6 @@
    "outputs": [],
    "source": [
     "import matplotlib.pyplot as plt\n",
-    "import seaborn as sns\n",
     "\n",
     "cov = res.sigma\n",
     "std = np.sqrt(np.diag(res.sigma)[:, None])\n",

requirements-dev.txt

@@ -6,6 +6,7 @@ isort>=5.12
 ipython
 matplotlib
 ruff
+jupyterlab-code-formatter
 flake8
 jupyter
 nbconvert