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chryswoodschryswoods
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I've merged in the notebooks from the last python_and_data workshop
and arranged them into a menu of options
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‎02_lists.ipynb‎

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Lists\n",
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"\n",
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"Lists provide a simple way to hold a collection of values. You create a list using square brackets. For example, here we can create a list that contains the values \"cat\", \"dog\" and \"horse\"\n",
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"\n",
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"```python\n",
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"a =[ \"cat\", \"dog\", \"horse\" ]\n",
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"```"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"a = [\"cat\", \"dog\", \"horse\"]"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"print(a)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"You can access the items in the list by placing the index of the item in square brackets. The first item is at index 0"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"a[0]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"The second item is at index 1, and the third item at index 2."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"a[2]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"What do you think will happen if we access the item at index 3?"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"a[3]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"You can also access the items in the list from the back. What do you think is at index -1?"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"a[-1]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"What about index -2, -3 or -4?"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"a[-3]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"You can add items onto a list by using the `.append` function. You can find this using tab completion and Python help..."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"help(a.append)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"a.append(\"fish\")"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"a"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"a[3]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"You can put whatever you want into a list, including other lists!"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"b = [ 42, 15, a, [7,8,9] ]"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"b[3]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Putting lists inside lists allows for multidimensional lookup, e.g. can you work out why `b[3][2]` equals `9`?"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"b[3][2]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"You can loop over the items in a list using a for loop, e.g."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"for x in a:\n",
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" print(x)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"You can get the number of items in the list using the `len` function."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"len(a)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"You can use this as an alternative way of looping over the elements of a list"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"for i in range(0,len(a)):\n",
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" print(a[i])"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"A string behaves like a list of letters. For example, if we have the string `s = \"Hello World\"`, then `s[0]` is \"H\" and `s[-1]` is d."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"s = \"Hello World\""
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"s[-1]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"You can loop over every letter in a string in the same way that you can loop over every item in a list."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"for letter in s:\n",
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" print(letter)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Exercises\n",
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"\n",
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"## Exercise 1\n",
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"\n",
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"Create two Python lists called `a` and `b`. Put into these lists the values [2, 4, 6, 8], and [10, 20, 30, 40].\n",
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"Check that `a[2]` equals `6` and `b[-1]` equals 40. (note that you will need to use the menu \"Insert | Insert Cell Below\" to insert more cells below to create space for your code)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": []
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Exercise 2\n",
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"\n",
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"Now create a loop that loops over each item in `a` and `b` and that calculates and prints out the product `a[i] * b[i]`."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": []
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Exercise 3\n",
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"\n",
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"Modify your code to create a list called `c`. Use the `.append` function to set `c[i] = a[i] * b[i]`. Check your code by making sure that `c[-1]` equals 320."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": []
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.5.3"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 2
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}

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