wk2/MY470_wk2_class.ipynb

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    "## MY470 Computer Programming\n",
    "# Working with Strings and Lists in Python\n",
    "### Week 2 Lab"
   ]
  },
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   "source": [
    "## Variables\n",
    "\n",
    "Variables associate objects (values) with a name. Objects have types (belong to classes). Here are the rules for naming variables:\n",
    "* Variables must begin with a letter (a - z, A - Z) or underscore (_)\n",
    "* Variables can contain letters, underscore, and numbers"
   ]
  },
  {
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   },
   "source": [
    "* Watch out for reserved words and names of functions!"
   ]
  },
  {
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   "execution_count": 4,
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   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "invalid syntax (<ipython-input-4-3ecf8fb15fb9>, line 7)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  File \u001b[1;32m\"<ipython-input-4-3ecf8fb15fb9>\"\u001b[1;36m, line \u001b[1;32m7\u001b[0m\n\u001b[1;33m    try = 3\u001b[0m\n\u001b[1;37m        ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m invalid syntax\n"
     ]
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   "source": [
    "# List of reserved words in Python: and, as, assert, break, \n",
    "# class, continue, def, del, elif, else, except, exec, \n",
    "# finally, for, from, global, if, import, in, is, lambda, not, \n",
    "# or, pass, print, raise, return, try, while, with, yield\n",
    " \n",
    "trial = 2\n",
    "try = 3\n",
    "\n",
    "# Note that the error below explains what the error is, and where exactly it is located.\n"
   ]
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     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3]\n"
     ]
    },
    {
     "ename": "TypeError",
     "evalue": "'list' object is not callable",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-23-e0cbabb1e82c>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m#list = [1, 2, 3] # Note the color of \"list\" - Python recognizes this but you are redefining it!\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      2\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mlist\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m \u001b[0mlist\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m10\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;36m20\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;36m30\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m \u001b[1;31m# The in-built function will no longer work\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m: 'list' object is not callable"
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    "list = [1, 2, 3] # Note the color of \"list\" - Python recognizes this but you are redefining it!\n",
    "list((10, 20, 30)) # The in-built function will no longer work"
   ]
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   "source": [
    "## Best Practice\n",
    "\n",
    "* 📖 Use **`UPPERCASE_WITH_UNDERSCORES`** for constants, like passwords or secret keys\n",
    "* 📖 Use **`lowercase_with_underscore`** for variable names, functions, and methods\n",
    "* 📖 Use **`UpperCamelCase`** for classes (coming in Week 5!) "
   ]
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   "source": [
    "## Resources\n",
    "\n",
    "In addition to the Python resources online, you can query any object to get help on what methods are available"
   ]
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     "text": [
      "Help on method_descriptor:\n",
      "\n",
      "popitem(self, /)\n",
      "    Remove and return a (key, value) pair as a 2-tuple.\n",
      "    \n",
      "    Pairs are returned in LIFO (last-in, first-out) order.\n",
      "    Raises KeyError if the dict is empty.\n",
      "\n"
     ]
    }
   ],
   "source": [
    "dir(dict)\n",
    "help(dict.popitem)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
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   "source": [
    "# Strings\n",
    "\n",
    "* Ordered sequences of characters\n",
    "* Immutable"
   ]
  },
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   "execution_count": 5,
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   "outputs": [
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     "text": [
      "My string\n",
      "s\n",
      "g\n",
      "My s\n",
      "y strin\n",
      "M tig\n",
      "git M\n"
     ]
    }
   ],
   "source": [
    "x = 'my string'\n",
    "\n",
    "# Capitalises the first character (chr) of the string\n",
    "x = x.capitalize()\n",
    "\n",
    "# prints the string\n",
    "print(x)\n",
    "\n",
    "# prints the chr at index 3\n",
    "print(x[3])\n",
    "\n",
    "# prints the last chr\n",
    "print(x[-1])\n",
    "\n",
    "# print a range \n",
    "# NOTE: not inclusive of the last index, 4 chrs because python starts at 0\n",
    "print(x[0:4])\n",
    "\n",
    "# Index one to the last index\n",
    "# Again, not inclusive\n",
    "print(x[1:-1])\n",
    "\n",
    "# EXTENDED SLICING \n",
    "# Get every other (2) item in the string.\n",
    "print(x[::2])\n",
    "\n",
    "# Reverse steps, every other chr\n",
    "print(x[::-2])\n"
   ]
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   "source": [
    "# Exercise 1: Make three new strings from the first and last, \n",
    "# second and second to last, and third and third to last letters \n",
    "# in the string below. Print the three strings.\n",
    "\n",
    "p = 'redder'\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
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   "source": [
    "# Exercise 2: Make a new string that is the same as string1 but \n",
    "# with the 8th and 22nd characters missing.\n",
    "\n",
    "string1 = 'I cancelled my travelling plans.'"
   ]
  },
  {
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   "source": [
    "## String Methods\n",
    "\n",
    "* `S.upper()`\n",
    "* `S.lower()`\n",
    "* `S.capitalize()`\n",
    "* `S.find(S1)`\n",
    "* `S.replace(S1, S2)`\n",
    "* `S.strip(S1)`\n",
    "* `S.split(S1)`\n",
    "* `S.join(L)`"
   ]
  },
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   "source": [
    "## Methods Can Be \"Stringed\"\n",
    "\n",
    "`sls = s.strip().replace('  ', ' ').upper().split()`\n",
    "\n",
    "However, be aware that this may reduce the clarity of your code. \n",
    "\n",
    "📖 It is largely a question of code legibility. \n",
    "\n",
    "⚡️ Except when you are working with large data — it is then also a question of memory."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
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   "outputs": [],
   "source": [
    "# Exercise 3: Remove the trailing white space in the string below, \n",
    "# replace all double spaces with single space, and format to a sentence \n",
    "# with proper punctuation. Print the resulting string.\n",
    "\n",
    "string1 = '  this  is a very badly.  formatted string -  I would  like to make it cleaner\\n'\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
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   "outputs": [],
   "source": [
    "# Exercise 4: Convert the string below to a list\n",
    "\n",
    "s = \"['apple', 'orange', 'pear', 'cherry']\"\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
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   "source": [
    "# Exercise 5: Reverse the strings below.\n",
    "\n",
    "s1 = 'stressed'\n",
    "s2 = 'drawer'"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
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   "source": [
    "# Lists\n",
    "\n",
    "* Ordered sequence of values\n",
    "* Mutable"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
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    "slideshow": {
     "slide_type": "-"
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4, 5]\n"
     ]
    }
   ],
   "source": [
    "mylist = [1, 2, 3, 4]\n",
    "mylist.append(5)\n",
    "print(mylist)"
   ]
  },
  {
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   "source": [
    "## List Methods\n",
    "\n",
    "* `L.append(e)`\n",
    "* `L.extend(L1)`\n",
    "* `L.insert(i, e)`\n",
    "* `L.remove(e)`\n",
    "* `L.pop(i)`\n",
    "* `L.sort()`\n",
    "* `L.reverse()`"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {
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   "outputs": [],
   "source": [
    "# Exercise 6: Use a list operation to create a list of ten elements, \n",
    "# each of which is '*'\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
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   "outputs": [],
   "source": [
    "# Exercise 7: Assign each of the three elements in the list below \n",
    "# to three variables a, b, c\n",
    "ls = [['dogs', 'cows', 'rabbits', 'cats'], 'eat', {'meat', 'grass'}]\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "# Exercise 8: Replace the last element in ls1 with ls2\n",
    "ls1 = [0, 0, 0, 1]\n",
    "ls2 = [1, 2, 3]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "outputs": [],
   "source": [
    "# Exercise 9: Create a new list that contains only unique elements from list x\n",
    "\n",
    "x = [1, 5, 4, 5, 6, 2, 3, 2, 9, 9, 9, 0, 2, 5, 7]\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "# Exercise 10: Print the elements that occur both in list a and list b\n",
    "\n",
    "a = ['red', 'orange', 'brown', 'blue', 'purple', 'green']\n",
    "b = ['blue', 'cyan', 'green', 'pink', 'red', 'yellow']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "# Exercise 11: Print the second smallest and the second largest numbers \n",
    "# in this list of unique numbers\n",
    "\n",
    "x = [2, 5, 0.7, 0.2, 0.1, 6, 7, 3, 1, 0, 0.3]\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "# Exercise 12: Create a new list c that contains the elements of \n",
    "# list a and b. Watch out for aliasing - you need to avoid it here.\n",
    "\n",
    "a = [1, 2, 3, 4, 5]\n",
    "b = ['a', 'b', 'c', 'd']\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
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   },
   "source": [
    "## Week 2 Assignment (SUMMATIVE)\n",
    "\n",
    "* Practice string and list manipulations\n",
    "* Practice working with data"
   ]
  }
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