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SCW-2019/ProgPy_Loops_filled.ipynb deleted 100644 → 0
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{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Repeating Actions with Loops"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"We found some suspicious features in our firs dataset \"inflammation-01.csv\". It is possible that other datasets are also affected by this?? We would like to check... Fast!"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Repeat tasks:"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"We have a lot of data sets and we have to tell the computer how to repeat things.\n",
"<br>\n",
"Let's first do something simpler: Show each character in a string!"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"l\n",
"e\n",
"a\n",
"d\n"
]
}
],
"source": [
"word = 'lead' # From wich number to wich number we had to go? Ask people\n",
"print(word[0])\n",
"print(word[1])\n",
"print(word[2])\n",
"print(word[3])"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Bad approach: tedious and if the string is larger it misses some characters, and if it shorter:"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"t\n",
"i\n",
"n\n"
]
},
{
"ename": "IndexError",
"evalue": "string index out of range",
"output_type": "error",
"traceback": [
"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[0;31mIndexError\u001b[0m Traceback (most recent call last)",
"\u001b[0;32m<ipython-input-2-61757d5ac451>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m 3\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mword\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 4\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mword\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m2\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 5\u001b[0;31m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mword\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m3\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
"\u001b[0;31mIndexError\u001b[0m: string index out of range"
]
}
],
"source": [
"word = 'tin' # Bad approach, if the string is larger it misses characters and if it shorter it fails!\n",
"print(word[0])\n",
"print(word[1])\n",
"print(word[2])\n",
"print(word[3])"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### There is a better approach: Recursion\n",
"Recursion is made by for loops:"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Example 1. A better way:"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"l\n",
"e\n",
"a\n",
"d\n"
]
}
],
"source": [
"word = 'lead'\n",
"for char in word:\n",
" print(char)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"The method supports strings of any lenght:"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"o\n",
"x\n",
"i\n",
"g\n",
"e\n",
"n\n"
]
}
],
"source": [
"word = 'oxigen'\n",
"for char in word:\n",
" print (char)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Let's see it in action:\n",
"<img src=\"https://scw-ss.github.io/python-novice-inflammation-2016-06-27-cfmehu/fig/loops_image.png\">"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### General form of a for-loop:\n"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"<img width=\"800px\" src=\"https://www.safaribooksonline.com/library/view/head-first-python/9781449397524/httpatomoreillycomsourceoreillyimages1368346.png.jpg\">"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"We can choose any name we want for variables. "
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"o\n",
"x\n",
"y\n",
"g\n",
"e\n",
"n\n"
]
}
],
"source": [
"word = 'oxygen'\n",
"for banana in word:\n",
" print(banana)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Example 2. This loop repeatedly updates a variable that acts as counter. It is very usual to find this structure:"
]
},
{
"cell_type": "code",
"execution_count": 8,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"There are 5 vowels\n"
]
}
],
"source": [
"lenght = 0\n",
"for vowel in 'aeiou': # The process details can be explained here\n",
" lenght = lenght + 1 # Explain what happens if lenght is inside\n",
"print('There are ',lenght,'vowels')"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"The for body is executed 5 times\n",
"<ul>\n",
"<li>1st: vowel eqs a; lenght eqs 1\n",
"<li>2st: vowel eqs e; lenght eqs 2\n",
"<li>etc.."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Off-topic tip: Some loops frecuently used are wraped inside very useful methods, such as <code>len</code> which returns the length of the variable. The methods avaiable by default in Python without import a thing are called <em>built-in</em> methods"
]
},
{
"cell_type": "code",
"execution_count": 9,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"5\n"
]
}
],
"source": [
"print(len('aeiou')) # built-in function to get the length of a string (and the length of many other things...). \n",
" # Is faster and much easier to read than a for loop"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Exercises"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### From 1 to N"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Python has a built-in function called range that creates a sequence of numbers. Using range, write a loop that uses range to print the first 3 odd natural numbers. Use the builtin help!"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"1\n",
"3\n",
"5\n"
]
}
],
"source": [
"for num in range(1,6,2):\n",
" print (num)"
]
}
],
"metadata": {
"kernelspec": {
"display_name": "Python 3",
"language": "python",
"name": "python3"
},
"language_info": {
"codemirror_mode": {
"name": "ipython",
"version": 3
},
"file_extension": ".py",
"mimetype": "text/x-python",
"name": "python",
"nbconvert_exporter": "python",
"pygments_lexer": "ipython3",
"version": "3.7.4"
}
},
"nbformat": 4,
"nbformat_minor": 1
}
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