notebooks/3_FlowControl_supplemental.ipynb

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      "source": [
        "# Python basics 3: Flow Control (supplemental)\n",
        "\n",
        "This notebook contains some additional materials for the topics of notebook 3."
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "DvV_db_dbpRh",
        "tags": []
      },
      "source": [
        "## Conditional statements, loops and functions\n"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "dfYI-vqpbpRq"
      },
      "source": [
        "### The Pass Statement\n",
        "\n",
        "Given the importance of indentation for Python, sometimes we may need a placeholder that allows us to write down a condition for an `if-then-else` construct or for a `while` loop without writing any statement (maybe just a comment). This is the case in which the `pass` statement comes in handy. \n",
        "\n",
        "In what follows, **nothing happens**:\n",
        "\n",
        "```python\n",
        "if condition1:\n",
        "    pass\n",
        "else:\n",
        "    pass\n",
        "```\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "id": "9enhPMzkbpRq"
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      "source": [
        "numbers = range(10)\n",
        "\n",
        "# Handy if you're quickly typing a loop\n",
        "# or function (see further on in this notebook)\n",
        "\n",
        "for n in numbers:\n",
        "    if n % 2 == 0:\n",
        "        pass  # TODO\n",
        "    else:\n",
        "        print(\"Odd!\")"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "X5_8X-9hbpRr"
      },
      "source": [
        "### List Comprehensions\n",
        "\n",
        "A list comprehension is a syntactic construct that allows us to create lists by applying a function on another list, in just **one line** of code. \n",
        "\n",
        "Even if the reverse isn't always true, list comprehensions can always be (inefficiently) expressed as loops. We will exploit this family resemblance for introducing this construct."
      ]
    },
    {
      "cell_type": "markdown",
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      "source": [
        "In what follows, we start with a list of numbers and we want to square all of its elements and save our final values in a new list."
      ]
    },
    {
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      "execution_count": null,
      "metadata": {
        "id": "xreE3ubQbpRr"
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      "outputs": [],
      "source": [
        "# Our source list\n",
        "source_list = [1,2,3,4,5,6,7,8,9]"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "id": "k-CrBOsEbpRr"
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      "outputs": [],
      "source": [
        "# We can solve this problem with a for loop...\n",
        "final_list = []\n",
        "\n",
        "for el in source_list:\n",
        "    final_list.append(el ** 2)\n",
        "\n",
        "print(final_list)"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "id": "eipfML2TbpRr"
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      "outputs": [],
      "source": [
        "# But this can also be done in one line\n",
        "final_list = [el ** 2 for el in source_list]\n",
        "\n",
        "print(final_list)"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "Z-2UhsqvbpRr"
      },
      "source": [
        "These list comprehensions cary the form of:\n",
        "    \n",
        "```python\n",
        "[i.method() for i in items]\n",
        "```"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "glykXGT9bpRr"
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      "source": [
        "**Conditional statements may be implemented**\n",
        "\n",
        "In what follows we want to ignore all the odd numbers"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "id": "_diIdh-vbpRs"
      },
      "outputs": [],
      "source": [
        "# We can solve this problem with a for loop...\n",
        "final_list = []\n",
        "\n",
        "for el in source_list:\n",
        "    if el % 2 == 0:\n",
        "        final_list.append(el ** 2)\n",
        "\n",
        "print(final_list)"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "id": "5xKe9qP7bpRs"
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      "outputs": [],
      "source": [
        "# ... or by using list comprehension\n",
        "final_list = [el ** 2 for el in source_list if el % 2 == 0]\n",
        "\n",
        "print(final_list)"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "g8zffkMybpRs"
      },
      "source": [
        "**If you want to implement an else clause the syntax changes slightly**\n",
        "\n",
        "In what follows we want to leave the odd numbers unchanged"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "id": "OXheeO4mbpRs"
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      "outputs": [],
      "source": [
        "# we can solve this problem with a for loop...\n",
        "final_list = []\n",
        "\n",
        "for el in source_list:\n",
        "    if el % 2 == 0:\n",
        "        final_list.append(el ** 2)\n",
        "    else:\n",
        "        final_list.append(el)\n",
        "\n",
        "print(final_list)"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "id": "RDwqq-yabpRs"
      },
      "outputs": [],
      "source": [
        "# ... or by using list comprehension\n",
        "final_list = [el ** 2 if el % 2 == 0 else el for el in source_list]\n",
        "\n",
        "print(final_list)"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "8E5dOz8KbpRs"
      },
      "source": [
        "### Quiz\n",
        "\n",
        "The following list contains 100 random extractions (with replacement) of numbers between 1 and 15. \n",
        "\n",
        "Find the number that has never been extracted"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "id": "Cv2ZrsaSbpRt"
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      "outputs": [],
      "source": [
        "random_numbers = [1, 2, 1, 1, 9, 13, 15, 5, 9, 8, 12, 14, 3, 2, 8, 10, 3, 12, 15, 13, 5, 3, 7, 5, 2, 13, 12, 8, 10, 5, 15, 8, 2, 8, 5, 12, 9, 2, 3, 5, 1, 4, 5, 9, 13, 2, 12, 5, 10, 8, 1, 15, 15, 6, 12, 3, 1, 3, 7, 14, 15, 10, 15, 7, 10, 12, 1, 2, 13, 7, 9, 6, 6, 7, 4, 12, 10, 8, 8, 3, 8, 4, 6, 14, 10, 5, 2, 3, 15, 4, 9, 3, 7, 7, 2, 4, 4, 1, 7, 15]"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "id": "XPH0Li2CbpRt"
      },
      "outputs": [],
      "source": [
        "# Your code here\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "kPgRBM5fbpRt"
      },
      "source": [
        "---"
      ]
    }
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