Reviewing Namespaces - Global Namespace.ipynb

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   "source": [
    "# Reviewing Namespaces: The Global Namespace\n",
    "\n",
    "What is a \"namespace\"? It is a collection of names that map to objects (variables, functions, etc...) that have been created in our code. Anytime we run a python script (or a jupyter notebook), a global namespace is created. We can print the names that are in the global namespace with the `dir()` function. Let's do that now, in the cell below, as we continue to learn about namespaces.\n",
    "\n",
    "Run the cell below and then notice what is printed out. These are all the names of the objects that are automatically created when you run a jupyter notebook.  We do not need to understand all of these (although, we might look at a one or two in the lecture); the main point here is that the global namespace exits and we can print its contents."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['In', 'Out', '_', '__', '___', '__builtin__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', '_dh', '_i', '_i1', '_ih', '_ii', '_iii', '_oh', 'exit', 'get_ipython', 'quit']\n"
     ]
    }
   ],
   "source": [
    "# use the dir() function to return the list of names in the namespace and use\n",
    "# print() to print that list.\n",
    "print(dir())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Adding our own names to the global namespace\n",
    "\n",
    "We can add our own names very easily, all we need to do is create a new object.  Everything in python is an object, so if we create a variable or a function or a instance of a class (we will cover classes later in the course) it will be added to the global namespace. Let's create a variable and then print the global namespace again and we will see the variable name is now in the global namespace."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['In', 'Out', '_', '__', '___', '__builtin__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', '_dh', '_i', '_i1', '_i2', '_ih', '_ii', '_iii', '_oh', 'exit', 'get_ipython', 'my_var', 'quit']\n"
     ]
    }
   ],
   "source": [
    "my_var = \"Will\"\n",
    "print(dir())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Names in a namespace are unique - you can not have duplicates\n",
    "\n",
    "If we assign the variable name `my_var` another value, we will not be able to use `my_var` to access the previous value. In other words, you can not have two variables named `my_var` in the same namespace. You can not have two objects with the same name in the same namespace. "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Let's now create a function and see that added to the global namespace"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['In', 'Out', '_', '__', '___', '__builtin__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', '_dh', '_i', '_i1', '_i2', '_i3', '_ih', '_ii', '_iii', '_oh', 'exit', 'get_ipython', 'my_var', 'quit', 'reverse_string']\n"
     ]
    }
   ],
   "source": [
    "def reverse_string(string):\n",
    "    '''Return the reverse of a string\n",
    "    '''\n",
    "    reverse_string = string[::-1]\n",
    "    return reverse_string\n",
    "\n",
    "print(dir())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "olleH\n"
     ]
    }
   ],
   "source": [
    "my_string = 'Hello'\n",
    "my_string_reversed = reverse_string(my_string)\n",
    "print(my_string_reversed)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['In', 'Out', '_', '__', '___', '__builtin__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', '_dh', '_i', '_i1', '_i2', '_i3', '_i4', '_i5', '_ih', '_ii', '_iii', '_oh', 'exit', 'get_ipython', 'my_string', 'my_string_reversed', 'my_var', 'quit', 'reverse_string']\n"
     ]
    }
   ],
   "source": [
    "print(dir())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Let's import a package and see that added to our namespace:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [],
   "source": [
    "import pandas"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['In', 'Out', '_', '__', '___', '__builtin__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', '_dh', '_i', '_i1', '_i2', '_i3', '_i4', '_i5', '_i6', '_i7', '_ih', '_ii', '_iii', '_oh', 'exit', 'get_ipython', 'my_string', 'my_string_reversed', 'my_var', 'pandas', 'quit', 'reverse_string']\n"
     ]
    }
   ],
   "source": [
    "print(dir())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Each package/module also has its own global namespace.\n",
    "This is important to understand. Each python module (a module is simply a .py file\n",
    "that contains functions, classes, and variables) has their own global namespace."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
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   "source": [
    "dir(pandas)"
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   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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