05-Conditionals.ipynb

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    "**Course Announcements**\n",
    "\n",
    "**Due Dates**\n",
    "- A1 due Monday (11:59 PM)\n",
    "- Submit CL1 & CL2 by end of Saturday if not already submitted\n",
    "\n",
    "**Survey (N=262)** \n",
    "- Time zones: 81% in PDT (UTC -7/8); 10% in Eastern Asia (UTC +8)\n",
    "- 68% have never programmed before\n",
    "- Hobbies: Gaming, hang with friends, baking/cooking, reading, music, beach, family\n",
    "- Futures: psychologist, researcher, grad school, engineer, undecided, happy, successful"
   ]
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    "**Q&A**\n",
    "\n",
    "Q: The \"slay the dragon\" example was confusing/too difficult.  \n",
    "A: That sounds really normal! Take time to think about new problems, attend Coding Lab & office hours and ask questions, and realize that knowledge comes mostly from *practice.*  \n",
    "\n",
    "Q: What is the purpose of Boolean logic? What can we use it for?  \n",
    "A: One place where we will use Booleans is with conditionals - covered in this lecture. You will see more uses for comparisons and Boolean logic as your code becomes more complex.  "
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   "source": [
    "# Conditionals\n",
    "\n",
    "- `if`\n",
    "- `elif`\n",
    "- `else`"
   ]
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   "source": [
    "## Conditionals: `if`"
   ]
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   "source": [
    "<div class=\"alert alert-success\">\n",
    "Conditionals are statements that check for a condition, using the <code>if</code> statement, and then only execute a set of code if the condition evaluates as <code>True</code>.\n",
    "</div>"
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    "condition = True\n",
    "\n",
    "if condition:\n",
    "    print('This code executes if the condition evaluates as True.')"
   ]
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   "source": [
    "# equivalent to above\n",
    "if condition == True:\n",
    "    print('This code executes if the condition evaluates as True.')"
   ]
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   "source": [
    "#### Poll Question #1\n",
    "\n",
    "Replace `---` below with something that will print 'True'\n",
    "\n",
    "- A) I did it!\n",
    "- B) I think I did it!\n",
    "- C) I tried but am stuck.\n",
    "- D) I'm unsure where to start"
   ]
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   "source": [
    "math = ---\n",
    "\n",
    "if math:\n",
    "    print('True')"
   ]
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   "source": [
    "## Conditional: `else`"
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   "source": [
    "<div class=\"alert alert-success\">\n",
    "After an <code>if</code>, you can use an <code>else</code> that will run if the conditional(s) above have not run.\n",
    "</div>"
   ]
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    "condition = False\n",
    "\n",
    "if condition:\n",
    "    print('This code executes if the condition evaluates as True.')\n",
    "else: \n",
    "    print('This code executes if the condition evaluates as False')"
   ]
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   "source": [
    "#### Poll Question #2\n",
    "\n",
    "Replace `---` below with something that will print 'False'.\n",
    "\n",
    "- A) I did it!\n",
    "- B) I think I did it!\n",
    "- C) I tried but am stuck.\n",
    "- D) I'm unsure where to start"
   ]
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   "source": [
    "my_value = ---\n",
    "\n",
    "if my_value:\n",
    "    print('True')\n",
    "else: \n",
    "    print('False')"
   ]
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   "source": [
    "## Conditional: `elif`"
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   "source": [
    "<div class=\"alert alert-success\">\n",
    "After an <code>if</code> statement, you can have any number of <code>elif</code>`s (meaning 'else if') to check other conditions.\n",
    "</div>"
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    "condition_1 = False\n",
    "condition_2 = True\n",
    "\n",
    "if condition_1:\n",
    "    print('This code executes if condition_1 evaluates as True.')\n",
    "elif condition_2:\n",
    "    print('This code executes if condition_1 did not evaluate as True, but condition_2 does.')\n",
    "else: \n",
    "    print('This code executes if both condition_1 and condition_2 evaluate as False')"
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   "source": [
    "### `elif` without an `else`\n",
    "\n",
    "An else statement is not required, but if both the `if` and the `elif` condtions are not met (both evaluate as `False`), then nothing is returned."
   ]
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    "condition_1 = False\n",
    "condition_2 = False\n",
    "\n",
    "if condition_1:\n",
    "    print('This code executes if condition_1 evaluates as True.')\n",
    "elif condition_2:\n",
    "    print('This code executes if condition_1 did not evaluate as True, but condition_2 does.')"
   ]
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   "source": [
    "### `elif` *after* an `else` does not make sense\n",
    "\n",
    "The order will always be `if`-`elif`-`else`...with only the `if` being required. If the `elif` is at the end...it will never be tested, as the `else` will have already returned a value once reached (and thus Python will throw an error)."
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    "## THIS CODE WILL PRODUCE AN ERROR\n",
    "condition_1 = False\n",
    "condition_2 = False\n",
    "\n",
    "if condition_1:\n",
    "    print('This code executes if condition_1 evaluates as True.')\n",
    "else: \n",
    "    print('This code executes if both condition_1 and condition_2 evaluate as False')\n",
    "elif condition_2:\n",
    "    print('This code executes if condition_1 did not evaluate as True, but condition_2 does.')"
   ]
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   "source": [
    "## Conditionals With Value Comparisons"
   ]
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   "source": [
    "<div class=\"alert alert-success\">\n",
    "Any expression that can be evaluated as a boolean, such as value comparisons, can be used with conditionals.\n",
    "</div>"
   ]
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    "language = \"s\"\n",
    "\n",
    "if language == \"Python\" or language == \"R\":\n",
    "    print(\"Yay!\")\n",
    "elif language == \"Perl\":\n",
    "    print(\"Hmmmmmmm\")\n",
    "else:\n",
    "    print(\"Get yourself a programming language!\")"
   ]
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    "# Exploring conditionals\n",
    "number = 4\n",
    "\n",
    "print('Before Conditional')\n",
    " \n",
    "if number < 5:\n",
    "    print('    if statement execution')\n",
    "elif number > 5:\n",
    "    print('    elif statement execution')\n",
    "\n",
    "print('After Conditional')"
   ]
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   "source": [
    "#### Poll Question #3\n",
    "\n",
    "What will the following code snippet print out?"
   ]
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    "condition = False\n",
    "\n",
    "if condition:\n",
    "    print(\"John\")\n",
    "elif not condition:\n",
    "    print(\"Paul\")\n",
    "elif not condition:\n",
    "    print(\"George\")\n",
    "else:\n",
    "    print(\"Ringo\")"
   ]
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   "source": [
    "- A) John \n",
    "- B) Paul, George, Ringo \n",
    "- C) Paul \n",
    "- D) Paul, George \n",
    "- E) Ringo"
   ]
  },
  {
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   "source": [
    "#### Poll Question #4\n",
    "\n",
    "What will the following code snippet print out?"
   ]
  },
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   "source": [
    "if 1 + 1 == 2:\n",
    "    print(\"I did Math\")\n",
    "elif 1/0:\n",
    "    print(\"I broke Math\")\n",
    "else:\n",
    "    print(\"I didn't do math\")"
   ]
  },
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   "source": [
    "- A) I did Math \n",
    "- B) I broke Math\n",
    "- C) I didn't do math\n",
    "- D) This code won't execute"
   ]
  },
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   },
   "source": [
    "#### Poll Question #5\n",
    "\n",
    "What will the following code snippet print out:"
   ]
  },
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    "conditional = False\n",
    "python = \"great\"\n",
    "\n",
    "if conditional:\n",
    "    if python == \"great\":\n",
    "        print(\"Yay Python!\")\n",
    "    else:\n",
    "        print(\"Oh no.\")\n",
    "else:\n",
    "    print(\"I'm here.\")"
   ]
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   "source": [
    "- A) Yay Python!\n",
    "- B) Oh no.\n",
    "- C) I'm here.\n",
    "- D) This code won't execute"
   ]
  },
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   "source": [
    "## Properties of conditionals\n",
    "\n",
    "- All conditionals start with an `if`, can have an optional and variable number of `elif`'s and an optional `else` statement\n",
    "- Conditionals can take any expression that can be evaluated as `True` or `False`. \n",
    "- At most one component (`if` / `elif` / `else`) of a conditional will run\n",
    "- The order of conditional blocks is always `if` then `elif`(s) then `else`\n",
    "- Code is only ever executed if the condition is met"
   ]
  }
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