update

module4.ipynb

@@ -152,13 +152,107 @@
     "\n",
     "./parameters.py one two three\n",
     "['./parameters.py', 'one', 'two', 'three']\n",
-    "…cat example \n",
+    "\n",
+    "\n",
+    "wc variables.py\n",
+    "7 19 174 variables.py \t\n",
+    "echo $?\n",
+    "0\n",
+    "\n",
+    "wc notpresent.sh\n",
+    "wc: notpresent.sh: No such file or directory\n",
+    "echo $?\n",
+    "1\n",
+    "\n",
+    "#!/usr/bin/env python3\n",
+    "\n",
+    "import os\n",
+    "import sys\n",
+    "\n",
+    "filename = sys.argv[1]\n",
+    "\n",
+    "if not os.path.exists(filename):\n",
+    "    with open(filename, \"w\") as f:\n",
+    "        f.write(\"New file created\\n\")\n",
+    "else:\n",
+    "    print(\"Error, the file {} already exists!\".format(filename))\n",
+    "    sys.exit(1)\n",
+    "\n",
+    "./create_file.py example\n",
+    "echo $?\n",
+    "0\n",
+    "\n",
+    "cat example \n",
     "New file created\n",
     "./create_file.py example\n",
     "Error, the file example already exists!\n",
     "echo $?\n",
     "1"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Python 2 and Python 3 handle input and raw_input differently.\n",
+    "\n",
+    "In Python 2\n",
+    "\n",
+    "- input(x) is roughly the same as eval(raw_input(x))\n",
+    "- raw_input() is preferred, unless the author wants to support evaluating string expressions.\n",
+    "- eval() is used to evaluate string expressions."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    ">>> my_number = input('Please Enter a Number: \\n')\n",
+    "Please Enter a Number: \n",
+    "123 + 1\n",
+    ">>> print(my_number)\n",
+    "123 + 1\n",
+    ">>> type(my_number)\n",
+    "<class 'str'>\n",
+    "\n",
+    "\n",
+    ">>> my_number = input('Please Enter a Number: \\n')\n",
+    "Please Enter a Number: \n",
+    "123 + 1\n",
+    ">>> print(my_number)\n",
+    "123 + 1\n",
+    ">>> eval(my_number)\n",
+    "124"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Subprocesses"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Running system commands in Python"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import subprocess\n",
+    "subprocess.run([\"date\"])\n",
+    "subprocess.run([\"sleep\", \"2\"])\n",
+    "result = subprocess.run([\"ls\", \"this_file_does_not_exist\"])\n",
+    "print(result.returncode)"
+   ]
   }
  ],
  "metadata": {