python_2.2_scripts_modules_and_packages.ipynb

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   "source": [
    "# Python: Scripts, modules, and packages"
   ]
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    "By this point, you may have a number of terms swirling in your head - let's work on clarifying the meaning of a number of these. A **script** is typically an executable piece of code - it can contain all of the things we've discussed so far, including functions, and may or may not return a result. A **module** is typically a library of pieces of code (functions, classes, etc.) and is not generally executable. Both scripts and modules are found in files ending in `.py` and Python can run those files. **Packages** are a collection of modules - typically a folder that contains multiple modules.\n",
    "\n",
    "We'll be using a number of packages and modules in this course. NumPy is a package that contains many numerical computation modules. Matplotlib is a package containing many helpful plotting modules. We'll need an understanding of how these work in order to use them effectively.\n",
    "\n",
    "Let's explore this further with a detailed discussion of modules. Let's keep in mind that packages are structured collections of modules that are accessed using similar import methods as discussed below.\n",
    "\n",
    "*The following text is modified from [The Python Tutorial](https://docs.python.org/3/tutorial/modules.html) from the Python Software Foundation.*\n",
    "\n",
    "Let's say you were using the Python interpreter, and you quit and then enter it again. The definitions you have made (functions and variables) are lost. Therefore, if you want to write a somewhat longer program, you are better off using a text editor to prepare the input for the interpreter and running it with that file as input instead. This is known as creating a *script*. As your program gets longer, you may want to split it into several files for easier maintenance. You may also want to use a handy function that you’ve written in several programs without copying its definition into each program.\n",
    "\n",
    "To support this, Python has a way to put definitions in a file and use them in a script or in an interactive instance of the interpreter. Such a file is called a *module*; definitions from a module can be *imported* into other modules or into the *main* module (the collection of variables that you have access to in a script executed at the top level and in calculator mode).\n",
    "\n",
    "A module is a file containing Python definitions and statements. The file name is the module name with the suffix `.py` appended. Within a module, the module’s name (as a string) is available as the value of the global variable `__name__`.\n",
    "\n",
    "Now, go to Spyder. Create a new file in your working directory and call it 'fibo.py'. Open 'fibo.py' in Spyder's text editor (can just double click the file in the file explorer) then copy and paste the code below into 'fibo.py' and save the file.\n",
    "\n",
    "*Note: before going forward, try writing your own function to generate a Fibonacci series - this is important practice*"
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   "source": [
    "# Fibonacci numbers module\n",
    "\n",
    "def fib(n):    # write Fibonacci series up to n\n",
    "    a, b = 0, 1\n",
    "    while b < n:\n",
    "        print(b, end=' ')\n",
    "        a, b = b, a+b\n",
    "    print()\n",
    "\n",
    "def fib2(n):   # return Fibonacci series up to n\n",
    "    result = []\n",
    "    a, b = 0, 1\n",
    "    while b < n:\n",
    "        result.append(b)\n",
    "        a, b = b, a+b\n",
    "    return result"
   ]
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    "Go to Spyder's IPython console and import the module you just created with the following command:"
   ]
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   "source": [
    "import fibo"
   ]
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   "source": [
    "Now, using the module name you can access both of the functions you created in 'fibo.py':"
   ]
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   "execution_count": 21,
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    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 \n"
     ]
    }
   ],
   "source": [
    "fibo.fib(1000)"
   ]
  },
  {
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "[1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]"
      ]
     },
     "execution_count": 22,
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     "output_type": "execute_result"
    }
   ],
   "source": [
    "fibo.fib2(100)"
   ]
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   "source": [
    "If you intend to use a function often you can assign it to a local name:"
   ]
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      "1 1 2 3 5 8 13 21 34 55 89 144 233 377 \n"
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   "source": [
    "fib = fibo.fib\n",
    "fib(500)"
   ]
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   "source": [
    "A module can contain executable statements as well as function definitions. These statements are intended to initialize the module. They are executed only the first time the module name is encountered in an import statement. [1] (They are also run if the file is executed as a script.)\n",
    "\n",
    "Each module has its own private symbol table, which is used as the global symbol table by all functions defined in the module. Thus, the author of a module can use global variables in the module without worrying about accidental clashes with a user’s global variables. On the other hand, if you know what you are doing you can touch a module’s global variables with the same notation used to refer to its functions, modname.itemname.\n",
    "\n",
    "Modules can import other modules. It is customary but not required to place all import statements at the beginning of a module (or script, for that matter). The imported module names are placed in the importing module’s global symbol table.\n",
    "\n",
    "There is a variant of the import statement that imports names from a module directly into the importing module’s symbol table. For example:"
   ]
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      "1 1 2 3 5 8 13 21 34 55 89 144 233 377 \n"
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   ],
   "source": [
    "from fibo import fib, fib2\n",
    "fib(500)"
   ]
  },
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   "source": [
    "This does not introduce the module name from which the imports are taken in the local symbol table (so in the example, `fibo` is not defined).\n",
    "\n",
    "There is even a variant to import all names that a module defines:"
   ]
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   "cell_type": "code",
   "execution_count": 25,
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     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1 1 2 3 5 8 13 21 34 55 89 144 233 377 \n"
     ]
    }
   ],
   "source": [
    "from fibo import *\n",
    "fib(500)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This imports all names except those beginning with an underscore (`_`). In most cases Python programmers do not use this facility since it introduces an unknown set of names into the interpreter, possibly hiding some things you have already defined.\n",
    "\n",
    "Note that in general the practice of importing `*` from a module or package is frowned upon, since it often causes poorly readable code. However, it is okay to use it to save typing in interactive sessions.\n",
    "\n",
    "If the module name is followed by `as`, then the name following `as` is bound directly to the imported module."
   ]
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  {
   "cell_type": "code",
   "execution_count": 26,
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     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1 1 2 3 5 8 13 21 34 55 89 144 233 377 \n"
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   ],
   "source": [
    "import fibo as fib\n",
    "fib.fib(500)"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This is effectively importing the module in the same way that `import fibo` will do, with the only difference of it being available as `fib`.\n",
    "\n",
    "It can also be used when utilizing `from` with similar effects:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
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    {
     "name": "stdout",
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     "text": [
      "1 1 2 3 5 8 13 21 34 55 89 144 233 377 \n"
     ]
    }
   ],
   "source": [
    "from fibo import fib as fibonacci\n",
    "fibonacci(500)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Next\n",
    "With functions, modules, packages, and scripts at our disposal, we only have one more significant category programming construct to discuss: objects and classes. These take some time to figure out and depend on all of the previous material, functions in particular, so make sure that you're feeling comfortable with the existing material before moving forward."
   ]
  }
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