intro-python.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Defensive programming"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This should fail due to the assertion that the inputs be positive values"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "ename": "AssertionError",
     "evalue": "Data should only contain positive values",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
      "Cell \u001b[0;32mIn[1], line 4\u001b[0m\n\u001b[1;32m      2\u001b[0m total \u001b[38;5;241m=\u001b[39m \u001b[38;5;241m0.0\u001b[39m\n\u001b[1;32m      3\u001b[0m \u001b[38;5;28;01mfor\u001b[39;00m num \u001b[38;5;129;01min\u001b[39;00m numbers:\n\u001b[0;32m----> 4\u001b[0m     \u001b[38;5;28;01massert\u001b[39;00m num \u001b[38;5;241m>\u001b[39m \u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mData should only contain positive values\u001b[39m\u001b[38;5;124m'\u001b[39m\n\u001b[1;32m      5\u001b[0m     total \u001b[38;5;241m+\u001b[39m\u001b[38;5;241m=\u001b[39m num\n\u001b[1;32m      6\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[38;5;124m'\u001b[39m\u001b[38;5;124mtotal is:\u001b[39m\u001b[38;5;124m'\u001b[39m, total)\n",
      "\u001b[0;31mAssertionError\u001b[0m: Data should only contain positive values"
     ]
    }
   ],
   "source": [
    "numbers = [1.5, 2.3, 0.7, -0.001, 4.4]\n",
    "total = 0.0\n",
    "for num in numbers:\n",
    "    assert num > 0.0, 'Data should only contain positive values'\n",
    "    total += num\n",
    "print('total is:', total)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Trying different kinds of assertions:\n",
    "- precondition\n",
    "    - must be true at start of function\n",
    "- postcondition\n",
    "    - something that must be true when the function finishes\n",
    "- invariant\n",
    "    - something that is always true at that particular point in the code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def normalize_rectangle(rect):\n",
    "    \"\"\"Normalizes a rectangle so that it is at the origin and 1.0 units long on its longest axis.\n",
    "    Input should be of the format (x0, y0, x1, y1).\n",
    "    (x0, y0) and (x1, y1) define the lower left and upper right corners\n",
    "    of the rectangle, respectively.\"\"\"\n",
    "    assert len(rect) == 4, 'Rectangles must contain 4 coordinates' # precondition\n",
    "    x0, y0, x1, y1 = rect\n",
    "    assert x0 < x1, 'Invalid X coordinates' # precondition\n",
    "    assert y0 < y1, 'Invalid Y coordinates' # precondition\n",
    "\n",
    "    dx = x1 - x0\n",
    "    dy = y1 - y0\n",
    "    if dx > dy:\n",
    "        scaled = dx / dy\n",
    "        upper_x, upper_y = 1.0, scaled\n",
    "    else:\n",
    "        scaled = dx / dy\n",
    "        upper_x, upper_y = scaled, 1.0\n",
    "\n",
    "    assert 0 < upper_x <= 1.0, 'Calculated upper X coordinate invalid' # postcondition\n",
    "    assert 0 < upper_y <= 1.0, 'Calculated upper Y coordinate invalid' # postcondition\n",
    "\n",
    "    return (0, 0, upper_x, upper_y)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Testing the preconditions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [
    {
     "ename": "AssertionError",
     "evalue": "Rectangles must contain 4 coordinates",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
      "Cell \u001b[0;32mIn[2], line 1\u001b[0m\n\u001b[0;32m----> 1\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[43mnormalize_rectangle\u001b[49m\u001b[43m(\u001b[49m\u001b[43m \u001b[49m\u001b[43m(\u001b[49m\u001b[38;5;241;43m0.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m1.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[38;5;241;43m2.0\u001b[39;49m\u001b[43m)\u001b[49m\u001b[43m)\u001b[49m) \u001b[38;5;66;03m# should fail precondition on line 6\u001b[39;00m\n",
      "Cell \u001b[0;32mIn[1], line 6\u001b[0m, in \u001b[0;36mnormalize_rectangle\u001b[0;34m(rect)\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[38;5;28;01mdef\u001b[39;00m \u001b[38;5;21mnormalize_rectangle\u001b[39m(rect):\n\u001b[1;32m      2\u001b[0m \u001b[38;5;250m    \u001b[39m\u001b[38;5;124;03m\"\"\"Normalizes a rectangle so that it is at the origin and 1.0 units long on its longest axis.\u001b[39;00m\n\u001b[1;32m      3\u001b[0m \u001b[38;5;124;03m    Input should be of the format (x0, y0, x1, y1).\u001b[39;00m\n\u001b[1;32m      4\u001b[0m \u001b[38;5;124;03m    (x0, y0) and (x1, y1) define the lower left and upper right corners\u001b[39;00m\n\u001b[1;32m      5\u001b[0m \u001b[38;5;124;03m    of the rectangle, respectively.\"\"\"\u001b[39;00m\n\u001b[0;32m----> 6\u001b[0m     \u001b[38;5;28;01massert\u001b[39;00m \u001b[38;5;28mlen\u001b[39m(rect) \u001b[38;5;241m==\u001b[39m \u001b[38;5;241m4\u001b[39m, \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mRectangles must contain 4 coordinates\u001b[39m\u001b[38;5;124m'\u001b[39m \u001b[38;5;66;03m# precondition\u001b[39;00m\n\u001b[1;32m      7\u001b[0m     x0, y0, x1, y1 \u001b[38;5;241m=\u001b[39m rect\n\u001b[1;32m      8\u001b[0m     \u001b[38;5;28;01massert\u001b[39;00m x0 \u001b[38;5;241m<\u001b[39m x1, \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mInvalid X coordinates\u001b[39m\u001b[38;5;124m'\u001b[39m \u001b[38;5;66;03m# precondition\u001b[39;00m\n",
      "\u001b[0;31mAssertionError\u001b[0m: Rectangles must contain 4 coordinates"
     ]
    }
   ],
   "source": [
    "print(normalize_rectangle( (0.0, 1.0,2.0))) # should fail precondition on line 6"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [
    {
     "ename": "AssertionError",
     "evalue": "Invalid X coordinates",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
      "Cell \u001b[0;32mIn[3], line 1\u001b[0m\n\u001b[0;32m----> 1\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[43mnormalize_rectangle\u001b[49m\u001b[43m(\u001b[49m\u001b[43m \u001b[49m\u001b[43m(\u001b[49m\u001b[38;5;241;43m4.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m2.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m1.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m5.0\u001b[39;49m\u001b[43m)\u001b[49m\u001b[43m \u001b[49m\u001b[43m)\u001b[49m) \u001b[38;5;66;03m# should fail precondition on line 8\u001b[39;00m\n",
      "Cell \u001b[0;32mIn[1], line 8\u001b[0m, in \u001b[0;36mnormalize_rectangle\u001b[0;34m(rect)\u001b[0m\n\u001b[1;32m      6\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m \u001b[38;5;28mlen\u001b[39m(rect) \u001b[38;5;241m==\u001b[39m \u001b[38;5;241m4\u001b[39m, \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mRectangles must contain 4 coordinates\u001b[39m\u001b[38;5;124m'\u001b[39m \u001b[38;5;66;03m# precondition\u001b[39;00m\n\u001b[1;32m      7\u001b[0m x0, y0, x1, y1 \u001b[38;5;241m=\u001b[39m rect\n\u001b[0;32m----> 8\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m x0 \u001b[38;5;241m<\u001b[39m x1, \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mInvalid X coordinates\u001b[39m\u001b[38;5;124m'\u001b[39m \u001b[38;5;66;03m# precondition\u001b[39;00m\n\u001b[1;32m      9\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m y0 \u001b[38;5;241m<\u001b[39m y1, \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mInvalid Y coordinates\u001b[39m\u001b[38;5;124m'\u001b[39m \u001b[38;5;66;03m# precondition\u001b[39;00m\n\u001b[1;32m     11\u001b[0m dx \u001b[38;5;241m=\u001b[39m x1 \u001b[38;5;241m-\u001b[39m x0\n",
      "\u001b[0;31mAssertionError\u001b[0m: Invalid X coordinates"
     ]
    }
   ],
   "source": [
    "print(normalize_rectangle( (4.0, 2.0, 1.0, 5.0) )) # should fail precondition on line 8"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [
    {
     "ename": "AssertionError",
     "evalue": "Invalid Y coordinates",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
      "Cell \u001b[0;32mIn[4], line 1\u001b[0m\n\u001b[0;32m----> 1\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[43mnormalize_rectangle\u001b[49m\u001b[43m(\u001b[49m\u001b[43m \u001b[49m\u001b[43m(\u001b[49m\u001b[38;5;241;43m0.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m1.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m2.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m1.0\u001b[39;49m\u001b[43m)\u001b[49m\u001b[43m)\u001b[49m) \u001b[38;5;66;03m# should fail precondition on line 9\u001b[39;00m\n",
      "Cell \u001b[0;32mIn[1], line 9\u001b[0m, in \u001b[0;36mnormalize_rectangle\u001b[0;34m(rect)\u001b[0m\n\u001b[1;32m      7\u001b[0m x0, y0, x1, y1 \u001b[38;5;241m=\u001b[39m rect\n\u001b[1;32m      8\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m x0 \u001b[38;5;241m<\u001b[39m x1, \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mInvalid X coordinates\u001b[39m\u001b[38;5;124m'\u001b[39m \u001b[38;5;66;03m# precondition\u001b[39;00m\n\u001b[0;32m----> 9\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m y0 \u001b[38;5;241m<\u001b[39m y1, \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mInvalid Y coordinates\u001b[39m\u001b[38;5;124m'\u001b[39m \u001b[38;5;66;03m# precondition\u001b[39;00m\n\u001b[1;32m     11\u001b[0m dx \u001b[38;5;241m=\u001b[39m x1 \u001b[38;5;241m-\u001b[39m x0\n\u001b[1;32m     12\u001b[0m dy \u001b[38;5;241m=\u001b[39m y1 \u001b[38;5;241m-\u001b[39m y0\n",
      "\u001b[0;31mAssertionError\u001b[0m: Invalid Y coordinates"
     ]
    }
   ],
   "source": [
    "print(normalize_rectangle( (0.0, 1.0, 2.0, 1.0))) # should fail precondition on line 9"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Testing postconditions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(0, 0, 0.2, 1.0)\n"
     ]
    }
   ],
   "source": [
    "print(normalize_rectangle( (0.0, 0.0, 1.0, 5.0))) # should pass postcondition because the rectangle is taller than it is wide"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [
    {
     "ename": "AssertionError",
     "evalue": "Calculated upper Y coordinate invalid",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
      "Cell \u001b[0;32mIn[6], line 1\u001b[0m\n\u001b[0;32m----> 1\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[43mnormalize_rectangle\u001b[49m\u001b[43m(\u001b[49m\u001b[43m \u001b[49m\u001b[43m(\u001b[49m\u001b[38;5;241;43m0.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m0.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m5.0\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m1.0\u001b[39;49m\u001b[43m)\u001b[49m\u001b[43m)\u001b[49m) \u001b[38;5;66;03m# should fail postcondition because the rectangle is wider than it is tall\u001b[39;00m\n",
      "Cell \u001b[0;32mIn[1], line 21\u001b[0m, in \u001b[0;36mnormalize_rectangle\u001b[0;34m(rect)\u001b[0m\n\u001b[1;32m     18\u001b[0m     upper_x, upper_y \u001b[38;5;241m=\u001b[39m scaled, \u001b[38;5;241m1.0\u001b[39m\n\u001b[1;32m     20\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m \u001b[38;5;241m0\u001b[39m \u001b[38;5;241m<\u001b[39m upper_x \u001b[38;5;241m<\u001b[39m\u001b[38;5;241m=\u001b[39m \u001b[38;5;241m1.0\u001b[39m, \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mCalculated upper X coordinate invalid\u001b[39m\u001b[38;5;124m'\u001b[39m\n\u001b[0;32m---> 21\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m \u001b[38;5;241m0\u001b[39m \u001b[38;5;241m<\u001b[39m upper_y \u001b[38;5;241m<\u001b[39m\u001b[38;5;241m=\u001b[39m \u001b[38;5;241m1.0\u001b[39m, \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mCalculated upper Y coordinate invalid\u001b[39m\u001b[38;5;124m'\u001b[39m\n\u001b[1;32m     23\u001b[0m \u001b[38;5;28;01mreturn\u001b[39;00m (\u001b[38;5;241m0\u001b[39m, \u001b[38;5;241m0\u001b[39m, upper_x, upper_y)\n",
      "\u001b[0;31mAssertionError\u001b[0m: Calculated upper Y coordinate invalid"
     ]
    }
   ],
   "source": [
    "print(normalize_rectangle( (0.0, 0.0, 5.0, 1.0))) # should fail postcondition on line 21 because the rectangle is wider than it is tall"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This tells us that there is something wrong with our calculations, so it's an assertion more to help the developer than the user. We can fix this error by correcting line 14 to divide dy by dx instead of dx by dy."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def normalize_rectangle(rect):\n",
    "    \"\"\"Normalizes a rectangle so that it is at the origin and 1.0 units long on its longest axis.\n",
    "    Input should be of the format (x0, y0, x1, y1).\n",
    "    (x0, y0) and (x1, y1) define the lower left and upper right corners\n",
    "    of the rectangle, respectively.\"\"\"\n",
    "    assert len(rect) == 4, 'Rectangles must contain 4 coordinates'\n",
    "    x0, y0, x1, y1 = rect\n",
    "    assert x0 < x1, 'Invalid X coordinates'\n",
    "    assert y0 < y1, 'Invalid Y coordinates'\n",
    "\n",
    "    dx = x1 - x0\n",
    "    dy = y1 - y0\n",
    "    if dx > dy:\n",
    "        scaled = dy / dx\n",
    "        upper_x, upper_y = 1.0, scaled\n",
    "    else:\n",
    "        scaled = dx / dy\n",
    "        upper_x, upper_y = scaled, 1.0\n",
    "\n",
    "    assert 0 < upper_x <= 1.0, 'Calculated upper X coordinate invalid'\n",
    "    assert 0 < upper_y <= 1.0, 'Calculated upper Y coordinate invalid'\n",
    "\n",
    "    return (0, 0, upper_x, upper_y)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(0, 0, 1.0, 0.2)\n"
     ]
    }
   ],
   "source": [
    "print(normalize_rectangle( (0.0, 0.0, 5.0, 1.0))) # now that we corrected our function this test passes too"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Test-driven development of range overlap function\n",
    "\n",
    "1. write function for each test\n",
    "2. write a `range_overlap` function that should pass tests\n",
    "3. if `range_overlap` produces any wrong answers, fix it and rerun test functions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def range_overlap(ranges): # define empty function\n",
    "    pass"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now we can establish some tests. For now, these should fail because `range_overlap` doesn't do anything"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [
    {
     "ename": "AssertionError",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
      "Cell \u001b[0;32mIn[10], line 2\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[38;5;66;03m# test statements\u001b[39;00m\n\u001b[0;32m----> 2\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m range_overlap([ (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m) ]) \u001b[38;5;241m==\u001b[39m (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m) \u001b[38;5;66;03m# test 1\u001b[39;00m\n\u001b[1;32m      3\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m range_overlap([ (\u001b[38;5;241m2.0\u001b[39m, \u001b[38;5;241m3.0\u001b[39m), (\u001b[38;5;241m2.0\u001b[39m, \u001b[38;5;241m4.0\u001b[39m)]) \u001b[38;5;241m==\u001b[39m (\u001b[38;5;241m2.0\u001b[39m, \u001b[38;5;241m3.0\u001b[39m) \u001b[38;5;66;03m# test 2\u001b[39;00m\n\u001b[1;32m      4\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m range_overlap([ (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m), (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m2.0\u001b[39m), (\u001b[38;5;241m-\u001b[39m\u001b[38;5;241m1.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m)]) \u001b[38;5;241m==\u001b[39m (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m) \u001b[38;5;66;03m# test 3\u001b[39;00m\n",
      "\u001b[0;31mAssertionError\u001b[0m: "
     ]
    }
   ],
   "source": [
    "# test statements\n",
    "assert range_overlap([ (0.0, 1.0) ]) == (0.0, 1.0) # test 1\n",
    "assert range_overlap([ (2.0, 3.0), (2.0, 4.0)]) == (2.0, 3.0) # test 2\n",
    "assert range_overlap([ (0.0, 1.0), (0.0, 2.0), (-1.0, 1.0)]) == (0.0, 1.0) # test 3"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "All of the tests above are cases where the inputs are valid and check that `range_overlap` does what we want. But what about if the inputs don't overlap?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "assert range_overlap([ (0.0, 1.0), (5.0, 6.0) ]) == None # no overlap\n",
    "assert range_overlap([ (0.0, 1.0), (1.0, 2.0)]) == None # touching but not overlapping"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The tutorial thinks these should fail still because `range_overlap` is still empty, but that isn't happening for me."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "range_overlap([(0.0, 1.0), (1.0, 2.0)])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Oh well, moving on.\n",
    "\n",
    "Let's actually make this function."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def range_overlap(ranges):\n",
    "    \"\"\"Return common overlap among a set of [left, right] ranges.\"\"\"\n",
    "    max_left = 0.0\n",
    "    min_right = 1.0\n",
    "    for (left, right) in ranges:\n",
    "        max_left = max(max_left, left)\n",
    "        min_right = min(min_right, right)\n",
    "    return (max_left, min_right)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "And let's make a test function so we don't have to run each assertion separately"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def test_range_overlap():\n",
    "    assert range_overlap([ (0.0, 1.0) ]) == (0.0, 1.0) # test 1\n",
    "    assert range_overlap([ (2.0, 3.0), (2.0, 4.0)]) == (2.0, 3.0) # test 2\n",
    "    assert range_overlap([ (0.0, 1.0), (0.0, 2.0), (-1.0, 1.0)]) == (0.0, 1.0) # test 3\n",
    "    assert range_overlap([ (0.0, 1.0), (5.0, 6.0) ]) == None # no overlap\n",
    "    assert range_overlap([ (0.0, 1.0), (1.0, 2.0)]) == None # touching but not overlapping\n",
    "    assert range_overlap([]) == None"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [
    {
     "ename": "AssertionError",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
      "Cell \u001b[0;32mIn[18], line 1\u001b[0m\n\u001b[0;32m----> 1\u001b[0m \u001b[43mtest_range_overlap\u001b[49m\u001b[43m(\u001b[49m\u001b[43m)\u001b[49m\n",
      "Cell \u001b[0;32mIn[16], line 3\u001b[0m, in \u001b[0;36mtest_range_overlap\u001b[0;34m()\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[38;5;28;01mdef\u001b[39;00m \u001b[38;5;21mtest_range_overlap\u001b[39m():\n\u001b[1;32m      2\u001b[0m     \u001b[38;5;28;01massert\u001b[39;00m range_overlap([ (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m) ]) \u001b[38;5;241m==\u001b[39m (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m) \u001b[38;5;66;03m# test 1\u001b[39;00m\n\u001b[0;32m----> 3\u001b[0m     \u001b[38;5;28;01massert\u001b[39;00m range_overlap([ (\u001b[38;5;241m2.0\u001b[39m, \u001b[38;5;241m3.0\u001b[39m), (\u001b[38;5;241m2.0\u001b[39m, \u001b[38;5;241m4.0\u001b[39m)]) \u001b[38;5;241m==\u001b[39m (\u001b[38;5;241m2.0\u001b[39m, \u001b[38;5;241m3.0\u001b[39m) \u001b[38;5;66;03m# test 2\u001b[39;00m\n\u001b[1;32m      4\u001b[0m     \u001b[38;5;28;01massert\u001b[39;00m range_overlap([ (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m), (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m2.0\u001b[39m), (\u001b[38;5;241m-\u001b[39m\u001b[38;5;241m1.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m)]) \u001b[38;5;241m==\u001b[39m (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m) \u001b[38;5;66;03m# test 3\u001b[39;00m\n\u001b[1;32m      5\u001b[0m     \u001b[38;5;28;01massert\u001b[39;00m range_overlap([ (\u001b[38;5;241m0.0\u001b[39m, \u001b[38;5;241m1.0\u001b[39m), (\u001b[38;5;241m5.0\u001b[39m, \u001b[38;5;241m6.0\u001b[39m) ]) \u001b[38;5;241m==\u001b[39m \u001b[38;5;28;01mNone\u001b[39;00m \u001b[38;5;66;03m# no overlap\u001b[39;00m\n",
      "\u001b[0;31mAssertionError\u001b[0m: "
     ]
    }
   ],
   "source": [
    "test_range_overlap()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "So we know we fail the second test, but we don't know if any of the tests after this fail, but at least we can go and solve this problem.\n",
    "\n",
    "We are definitely causing an issue because we are initializing with values that aren't related to the data! **Always initialize from data**"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Debugging\n",
    "\n",
    "Well I did type up thoughts as I worked on it, but then I forgot to save it before committing."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Command-line programs\n",
    "\n",
    "Again with the not saving...\n",
    "\n",
    "Since I didn't both with the data for the tutorial, I'm just going to put the code for this here rather than a code chunk.\n",
    "\n",
    "We can set up a script to run as a program, let's say it's called `code.py`\n",
    "```\n",
    "import sys\n",
    "import numpy\n",
    "\n",
    "def main():\n",
    "    script = sys.argv[0]\n",
    "    filename = sys.argv[1]\n",
    "    data = numpy.loadtxt(filename, delimiter=',')\n",
    "    for row_mean in numpy.mean(data, axis=1):\n",
    "        print(row_mean)\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    main()\n",
    "```\n",
    "\n",
    "Now we can run this from the terminal with `python code.py test.csv` to get the row means from the `test.csv` file.\n",
    "\n",
    "The `if __name__ == '__main__': main()` portion of the script allows us to distinguish between a file being imported (in which case `__name__` is the file name) and running the file as a script (in which case `__name__` is set to `__main__`).\n",
    "\n",
    "### Handling multiple files\n",
    "\n",
    "We can loop over multiple input files with a loop over `sys.argv[1:]`\n",
    "\n",
    "```\n",
    "import sys\n",
    "import numpy\n",
    "\n",
    "def main():\n",
    "    script = sys.argv[0]\n",
    "    for filename in sys.argv[1:]:\n",
    "        data = numpy.loadtxt(filename, delimiter = ',')\n",
    "        for row_mean in numpy.mean(data, axis = 1):\n",
    "            print(row_mean)\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    main()\n",
    "```\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "\n",
    "### Handling command-line flags\n",
    "Now we can add flags:\n",
    "\n",
    "```\n",
    "import sys\n",
    "import numpy\n",
    "\n",
    "def main():\n",
    "    script = sys.argv[0]\n",
    "    action = sys.argv[1]\n",
    "    filenames = sys.argv[2:]\n",
    "\n",
    "    for filename in filenames:\n",
    "        data = numpy.loadtxt(filename, delimiter = ',')\n",
    "\n",
    "        if action == '--min':\n",
    "            values = numpy.amin(data, axis = 1)\n",
    "        elif action == '--mean':\n",
    "            values = numpy.mean(data, axis = 1)\n",
    "        elif action == '--max':\n",
    "            values = numpy.amax(data, axis = 1)\n",
    "        \n",
    "        for val in values:\n",
    "            print(val)\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    main()\n",
    "```\n",
    "\n",
    "Now we can run commands like: `python code.py --max test.csv` to get the maximum values of each row of `test.csv`.\n",
    "\n",
    "But there are some issues that this set up causes. We are passing arguments with an assumption about how many flags and in what order various inputs are provided. Also the `main()` function is long and not very readable and there is no way to check that the action flag will actually result in an output.\n",
    "\n",
    "```\n",
    "import sys\n",
    "import numpy\n",
    "\n",
    "def main():\n",
    "    script = sys.argv[0]\n",
    "    action = sys.argv[1]\n",
    "    filenames = sys.argv[2:]\n",
    "\n",
    "    assert action in ['--min', '--mean', '--max'], \\\n",
    "        'Action is not one of --min, --mean, or --max: ' + action\n",
    "    \n",
    "    for filename in filenames:\n",
    "        process(filename, action)\n",
    "\n",
    "def process(filename, action):\n",
    "    data = numpy.loadtxt(filename, delimiter = ',')\n",
    "\n",
    "    if action == '--min':\n",
    "        values = numpy.amin(data, axis = 1)\n",
    "    elif action == '--mean':\n",
    "        values = numpy.mean(data, axis = 1)\n",
    "    elif action == '--max':\n",
    "        values = numpy.amax(data, axis = 1)\n",
    "    \n",
    "    for val in values:\n",
    "        print(val)\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    main()\n",
    "```\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Handling standard input\n",
    "Now let's use standard input so that this can be used in a pipeline with inputs redirected to it.\n",
    "\n",
    "For this we will use a new script `count_stdin.py`\n",
    "```\n",
    "import sys\n",
    "\n",
    "count = 0\n",
    "for line in sys.stdin:\n",
    "    count += 1\n",
    "\n",
    "print(count, 'lines in standard input')\n",
    "```\n",
    "\n",
    "We will use this a little differently: `python count_stdin.py < test.csv` rather than `python count_stdin.py test.csv`. The `<` redirects the file to standard input.\n",
    "\n",
    "Now we can rewrite our previous program so that it will load in data from `sys.stdin` if there isn't a filename provided. We don't need to make any changes to the `process()` function, we just need to tell the `main()` function how to handle a lack of filenames.\n",
    "\n",
    "```\n",
    "import sys\n",
    "import numpy\n",
    "\n",
    "def main():\n",
    "    script = sys.argv[0]\n",
    "    action = sys.argv[1]\n",
    "    filenames = sys.argv[2:]\n",
    "    assert action in ['--min', '--mean', '--max'], \\\n",
    "           'Action is not one of --min, --mean, or --max: ' + action\n",
    "    if len(filenames) == 0:\n",
    "        process(sys.stdin, action)\n",
    "    else:\n",
    "        for filename in filenames:\n",
    "            process(filename, action)\n",
    "\n",
    "def process(filename, action):\n",
    "    data = numpy.loadtxt(filename, delimiter = ',')\n",
    "\n",
    "    if action == '--min':\n",
    "        values = numpy.amin(data, axis=1)\n",
    "    elif action == '--mean':\n",
    "        values = numpy.mean(data, axis=1)\n",
    "    elif action == '--max':\n",
    "        values = numpy.amax(data, axis=1)\n",
    "\n",
    "    for val in values:\n",
    "        print(val)\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    main()\n",
    "```"
   ]
  }
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