1_loops.ipynb

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    "# Loops\n",
    "\n",
    "\n",
    "- prepared by [Katarina Nastou](https://www.cpr.ku.dk/staff/?pure=en/persons/672471)\n",
    "\n",
    "[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/pythontsunami/teaching/blob/intro/1_loops.ipynb)"
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    "\n",
    "## Objectives\n",
    "- Understand what loops are and how they are useful\n",
    "- Learn what an \"iterable object\" is\n",
    "- Use ***for*** and ***while*** loops to iterate over ranges and strings \n",
    "- Learn how to control exiting a loop\n",
    "\n"
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    "Test: Print numbers 1 through 10 using what you already know"
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    "print(1)\n",
    "print(2)\n",
    "print(3)\n",
    "print(4)\n",
    "print(5)\n",
    "print(6)\n",
    "print(7)\n",
    "print(8)\n",
    "print(9)\n",
    "print(10)"
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    "> This notebook is about how to do less tediously."
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    "## **`for`** loops\n",
    "In Python, [**`for`**](https://docs.python.org/3/tutorial/controlflow.html#for-statements) loops are written like this:\n",
    "\n",
    "```python\n",
    "for item in iterable_object:\n",
    "    # do something with item\n",
    "```\n",
    "- An **iterable object** is some kind of collection of items, for instance: a `str`ing of characters, a `range`, a [`list`](1_lists.ipynb) etc.\n",
    "- ***item*** is a new variable that can be called whatever you want\n",
    "- ***item*** references the current position of our ***iterator*** within the iterable. It will iterate over (run through) every item of the collection and then go away when it has visited all items\n",
    "- the body of the loop is **indented** to group statements."
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    "# str(), range(1), list()"
   ]
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    "## ***for*** loops with **ranges**\n",
    "Let's print numbers 1 - 10 using ranges."
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    "for number in range(1, 11):\n",
    "    print(number)"
   ]
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    "## ranges\n",
    "If we just want to print numbers, we can simply iterate over a range.\n",
    "\n",
    "Python ranges come in multiple forms:\n",
    "\n",
    "- `range(8)` gives you integers from 0 through 7 (Count starts at 0 and is exclusive)\n",
    "\n",
    "- `range(2, 9)` will give you integers from 2 to 8 (Two parameters are (start, end))\n",
    "\n",
    "- `range(10, 20, 2)`  will give you odds from 10 to 20\n",
    "\n",
    "- `range(9, 0, -1)`  will give you integers from 9 to 1 (Third parameter is the \"step\", meaning how many to skip. Also, which way to count, up + or down -)\n"
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    "## Quiz\n",
    "- *Question 1*: What numbers does the following range generate?\n",
    "`range(6,12)` \n",
    "\n",
    "- *Question 2*: What numbers does the following range generate?\n",
    "`range(4)` \n",
    "\n",
    "- *Question 3*: What is printed out after the following code?\n",
    "```\n",
    "nums = range(1,5)\n",
    "print(nums)\n",
    "```\n",
    "tip: run the code to check for yourself!\n",
    "\n",
    "- *Question 4*: What numbers does the following range generate: `range(12,0,-3)`"
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    "### Exercise 1\n",
    "Loop through numbers 1-20:\n",
    "- for 4 and 13, print \"x is unlucky\"\n",
    "- for even numbers, print \"x is even\"\n",
    "- for odd numbers, print \"x is odd\"\n",
    "\n",
    "> check [`1_conditionals.ipynb`](1_conditionals.ipynb)"
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    "## ***while*** loops\n",
    "\n",
    "We can also iterate using a **`while`** loop, which has a different format:\n",
    "\n",
    "```python\n",
    "while im_tired:\n",
    "    # drink coffee\n",
    "```\n",
    "while loops continue to execute while a certain condition is True, and will end when it becomes False.\n",
    "\n",
    "```python\n",
    "user_response = \"Something...\"\n",
    "while user_response != \"please\":\n",
    "    user_response = input(\"Ah ah ah, you didn't say the magic word: \")\n",
    "```\n",
    "\n",
    "***while*** loops require more careful setup than ***for*** loops, since you have to specify the termination conditions manually.\n",
    "\n",
    "Be careful! If the condition doesn't become false at some point, your loop will continue ***forever***!\n"
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    "## Quiz\n",
    "\n",
    "**Question 1**: What does the following loop do?\n",
    "```python\n",
    "    i = 1\n",
    "    while i < 5:\n",
    "        i + i\n",
    "        print(i)\n",
    "```\n",
    "    \n",
    "> hint: is the value of i changing?"
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    "**Question 2**: What does the following loop do?\n",
    "```python\n",
    "    i = 0\n",
    "    while i <= 5:\n",
    "        i =+ 1\n",
    "        print(i)\n",
    "```\n",
    "> hint: have you checked for typos here?"
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    "**Question 3**: What can we do to get out of the infinite loop below?\n",
    "```python\n",
    "    # this code runs forever...\n",
    "    x = 0\n",
    "    while x != 11:\n",
    "        x += 2\n",
    "        print(x)\n",
    "```\n",
    "\n",
    "1. change the condition to `x != 10`\n",
    "   \n",
    "2. change the condition to `x < 11`\n",
    "    \n",
    "3. add conditional that says \n",
    "    \n",
    "```python\n",
    "if x == 10:\n",
    "    break\n",
    "```\n",
    "\n",
    "4. press Ctrl + C to kill the program\n",
    "\n",
    "5. all of the above"
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    "## Controlled Exit\n",
    "\n",
    "\n",
    "The keyword [`break`](https://docs.python.org/3/tutorial/controlflow.html#break-and-continue-statements-and-else-clauses-on-loops) gives us the ability to exit out of while loops whenever we want:\n",
    "\n",
    "```python\n",
    "while True:\n",
    "    command = input(\"Type 'exit' to exit: \")\n",
    "    if (command == \"exit\"):\n",
    "        break\n",
    "```\n",
    "\n",
    "We can also use it to end for loops early:\n",
    "\n",
    "```python\n",
    "for x in range(1, 101):\n",
    "    print(x)\n",
    "    if x == 3:\n",
    "        break\n",
    "```"
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    "### Adding a break"
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    "times = int(input(\"Give me a number from 10 to 100 to count to and you can hide: \"))\n",
    "\n",
    "for time in range(times):\n",
    "    print(str(time+1)+\" missisipi\")\n",
    "    if time+1 == 5: \n",
    "        print(\"Hahaha I won't count that far!\")\n",
    "        break"
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    "## Recap\n",
    "\n",
    "- Loops are sections of code that keep repeating\n",
    "- For loops are useful for going through [iterable objects](https://docs.python.org/3/tutorial/classes.html#iterators)\n",
    "- While loops are more versatile but require more set up\n",
    "- Any loop can be short-circuited with the `break` keyword\n",
    "\n",
    "\n",
    "\n"
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    "*Note: This notebook's contents have been adapted from Colt Steele's slides used in [Modern Python 3 Bootcamp Course](https://www.udemy.com/course/the-modern-python3-bootcamp/) on Udemy*"
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