Homework1-PythonUnitConverter.ipynb

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    "# Python-Powered Unit Converter\n",
    "Adapted from [original assignment](https://selfpaced.bitbucket.io/#/python/assignment/python-powered-unit-converter) by Dan Garcia\n",
    "\n",
    "## Background\n",
    "\n",
    "Let's take a trip back in time. Imagine you're a high-paid engineer for NASA, and the date is late September, 1999. The entire agency is all abuzz with the prospect of the Mars Climate Orbiter, launched more than nine months ago, reaching a stable orbit around our neighboring red planet and sending back important weather data. \n",
    "    \n",
    "![Mars Climate Orbiter](https://www.jpl.nasa.gov/missions/web/mars_climate_orbiter.jpg)\n",
    "\n",
    "<center>Figure 1. Illustration of the Mars Climate Orbiter</center>\n",
    "\n",
    "On September 23, 1999, your team loses the signal to this multi-million dollar orbiter. In November, after a lengthy investigation, you inform the press of the reasons for the crash: data in a software file for calculating trajectory forces was in English units of pound-seconds (lbf-s), but the thruster was expecting the data to be in metric units of Newton-seconds (N-s).\n",
    "\n",
    "History records the experience as one of the most egregious and expensive bugs of all time. Engineers and computer scientists the world over vow to be diligent to check, double-check and triple-check the units in their calculations.\n",
    "\n",
    "## Your Task\n",
    "\n",
    "For this project, you'll write a Python program to do unit conversion—provide the translation of a quantity specified by a certain amount in one source unit (convert from) and a destination unit (convert to). That is, your program should be able to answer the common question (and many more like it): How many meters in 10 miles? (answer: 10 miles = 16,093.44 m)\n",
    "\n",
    "To make the input easy, you can use the `ipywidgets` below, which constrain the user input to be in the form of one float, a starting unit to convert from, and a unit to convert to. Three categories of units are included in the input options: distances, weights, and volumes.\n",
    "\n",
    "## Requirements\n",
    "\n",
    "- 1) **Welcome text for your program** Above the provided widgets, add a welcome message and instructions for the user. You can use triple quotes to create and then print a multi-line string. This is the only thing you need to add to the starter code in the next cell. Everything else can be implemented in a new cell below that. \n",
    "\n",
    "    - Instructions should include a list of the supported categories and units within that category so the user knows what to do. You can use the options given to the input widgets for reference.\n",
    "\n",
    "- 2) The input widets currently allow `convertFrom.value` and `convertTo.value` to be from mismatching categories (e.g., convert distance to weight). **Check if the categories match** if so, great, your program can move on. Otherwise, display a friendly, helpful message to the user with instructions on how to try again.\n",
    "\n",
    "    - `convertFrom.value` and `convertTo.value` are only evaluated when the code cell is executed initially, not while the cell is running. You may include instructions in your message to the user to gracefully exit (not by pressing stop), double-check that their units match, and run the cell containing your program again\n",
    "    - It's okay to ask a user to run a code cell. Your program should _not_ result in any errors or require the user to stop and restart a cell.\n",
    "\n",
    "- 3) Write your program to **calculate the unit conversion**. \n",
    "    - To get the values of the input widgets, you can use `value.value`, `convertFrom.value`, and `convertTo.value` because the widgets are named value, convertFrom, and convertTo respectively and they have a property called value that is updated each time a user interacts with that widget. Again, the value is update in real time, but a code cell that is currently running while the widget is updated will not register the update. \n",
    "    - I highly recommend designing a game plan for how you _will_ write your code before you start programming. See Potential Approaches below for more advice.\n",
    "- 4) Each portion of your code that satisfies an above requirement should be documented with comments.\n",
    "\n",
    "## Where to find the conversion constants\n",
    "\n",
    "There are many websites and books with conversion constants listed, so feel free to get this data any way you wish. One great source is Google. You can use Google to find out how many source units are in a destination unit by typing \"1 source_unit in destination_unit\" and build structures into your program to store these answers. See the Hints section below to see how we suggest you approach the internal details of storing the information.\n",
    "\n",
    "At this point, you might wonder why we're doing all this work if Google can do it for us. First, we don't always have access to the Internet. Second, it's a valuable beginning programming activity. \n",
    "\n",
    "## Potential Approaches\n",
    "\n",
    "How should you store all of the multiplying factors between units? There's the hard way and the easy way to think about it. The particular Python data type you should use is something you should consider on your own.\n",
    "\n",
    "### The Hard Way\n",
    "\n",
    "The hard way is to build an internal two-dimensional table structure of the conversion of every unit to every other unit for every category. This is really painful. Imagine how many translators the United Nations would need if they had 1,000 people speaking different languages and they used this model...a million people!\n",
    "\n",
    "### The Easy Way\n",
    "\n",
    "The easy way is to find a common, base unit (e.g., meters for distances) and then just store the constant (e.g., 1000 for kilometers) that is used to convert from the base unit to that unit. To convert from two units in the same category (neither of which are the base unit), you simply convert from your convertFrom unit to the base unit, then from that to the convertTo unit. Using the previous analogy you'd only need to hire 1,000 translators at the UN -- as long as each could translate to and from their language to a common language, like one of the click languages.\n",
    "\n",
    "### Checklist\n",
    "\n",
    "Make sure your program accounts for all of the following to get full credit.\n",
    "\n",
    "- Use of functions—your program must be broken down into one or more functions—it cannot be one big long script.\n",
    "- Each function has a docstring that summarizes its purpose and provides a description of its inputs and outputs.\n",
    "- All functions and variables have meaningful names.\n",
    "- Do not use excessive if statements where you could leverage a dictionary.\n",
    "- Preserved output showing the program produces correct translations among all the units of a category, i.e., call your function multiple times from different cells and don't restart the kernel before saving and submitting your notebook.\n",
    "- All of the features listed in the Requirements section above."
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    "# First, run this cell to generate input widgets\n",
    "\n",
    "import ipywidgets as widgets\n",
    "\n",
    "value = widgets.FloatText(\n",
    "    value=10.0,\n",
    "    description='Convert: ',\n",
    "    disabled=False\n",
    ")\n",
    "\n",
    "convertFrom = widgets.Dropdown(\n",
    "    options=['ft', 'cm', 'mm', 'mi', 'm', 'yd', 'km', 'in', #distances\n",
    "             'lb', 'mg','kg', 'oz', 'g', #weights\n",
    "             'floz', 'qt', 'cup', 'mL', 'L', 'gal', 'pint'],#volumes\n",
    "    value='mi',\n",
    "    description='',\n",
    "    disabled=False,\n",
    ")\n",
    "\n",
    "convertTo = widgets.Dropdown(\n",
    "    options=['ft', 'cm', 'mm', 'mi', 'm', 'yd', 'km', 'in', #distances\n",
    "             'lb', 'mg','kg', 'oz', 'g', #weights\n",
    "             'floz', 'qt', 'cup', 'mL', 'L', 'gal', 'pint'],#volumes\n",
    "    value='m',\n",
    "    description='to ',\n",
    "    disabled=False,\n",
    ")\n",
    "\n",
    "# Welcome message here\n",
    "...\n",
    "\n",
    "items = [value, convertFrom, convertTo]\n",
    "left_box = widgets.VBox([items[0], items[2]])\n",
    "right_box = widgets.VBox([items[1]])\n",
    "widgets.HBox([left_box, right_box])"
   ]
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