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‎.ipynb_checkpoints/Booleans-checkpoint.ipynb

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‎.ipynb_checkpoints/Files-checkpoint.ipynb

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{
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"cells": [],
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"metadata": {},
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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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"# Files\n",
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"\n",
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"Python uses file objects to interact with external files on your computer. These file objects can be any sort of file you have on your computer, whether it be an audio file, a text file, emails, Excel documents, etc. Note: You will probably need to install certain libraries or modules to interact with those various file types, but they are easily available. (We will cover downloading modules later on in the course).\n",
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"\n",
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"Python has a built-in open function that allows us to open and play with basic file types. First we will need a file though. We're going to use some iPython magic to create a text file!\n",
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"\n",
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"## iPython Writing a File"
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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": 6,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Overwriting test.txt\n"
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]
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}
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],
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"source": [
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"%%writefile test.txt\n",
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"Hello, this is a quick test file"
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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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"## Python Opening a file\n",
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"\n",
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"We can open a file with the open() function. The open function also takes in arguments (also called parameters). Lets see how this is used:"
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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": 14,
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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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"# Open the text.txt we made earlier\n",
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"my_file = open('test.txt')"
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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": 15,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"'Hello, this is a quick test file'"
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]
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},
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"execution_count": 15,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"# We can now read the file\n",
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"my_file.read()"
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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": 16,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"''"
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]
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},
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"execution_count": 16,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"# But what happens if we try to read it again?\n",
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"my_file.read()"
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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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"This happens because you can imagine the reading \"cursor\" is at the end of the file after having read it. So there is nothing left to read. We can reset the \"cursor\" like this:"
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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": 42,
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"metadata": {
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"collapsed": false
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},
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"outputs": [],
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"source": [
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"# Seek to the start of file (index 0)\n",
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"my_file.seek(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": 19,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"'Hello, this is a quick test file'"
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]
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},
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"execution_count": 19,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"# Now read again\n",
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"my_file.read()"
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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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"In order to not have to reset every time, we can also use the readlines method. Use this with caution ofr large files, since everything will be held in memory. We will learn how to iterate over large files later in the course."
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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": 26,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"['Hello, this is a quick test file']"
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]
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},
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"execution_count": 26,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"# Readlines returns a list of the lines in the file.\n",
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"my_file.readlines()"
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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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"## Writing to a File\n",
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"\n",
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"By default, using the open() function will only allow us to read the file, we need to pass the argument 'w' to write over the file. For example:"
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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": 39,
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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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"# Add a second argument to the function, 'w' which stands for write\n",
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"my_file = open('test.txt','w+')"
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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": 40,
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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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"# Write to the file\n",
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"my_file.write('This is a new line')"
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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": 43,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"'This is a new line'"
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]
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},
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"execution_count": 43,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"# Read the file\n",
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"my_file.read()"
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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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"## Iterating through a File\n",
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"\n",
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"Lets get a quick preview of a for loop by iterating over a text file. First let's make a new text file with some iPython Magic:"
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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": 44,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Overwriting test.txt\n"
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]
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}
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],
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"source": [
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"%%writefile test.txt\n",
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"First Line\n",
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"Second Line"
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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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"Now we can use a little bit of flow to tell the program to for through every line of the file and do something:"
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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": 45,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"First Line\n",
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"\n",
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"Second Line\n"
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]
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}
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],
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"source": [
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"for line in open('test.txt'):\n",
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" print line"
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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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"Don't worry about fully understanding this yet, for loops are coming up soon. But we'll break down what we did above. We said that for every line in this text file, go ahead and print that line. Its important to note a few things here:\n",
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"\n",
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" 1.) We could have called the 'line' object anything (see example below).\n",
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" 2.) By not calling .read() on the file, the whole text file was not stored in memory.\n",
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" 3.) Notice the indent on the second line for print. This whitespace is required in Python.\n",
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"\n",
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"We'll learn a lot more about this later, but up next: Sets and Booleans!"
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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": 46,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"First Line\n",
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"\n",
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"Second Line\n"
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]
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}
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],
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"source": [
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"# Pertaining to the first point above\n",
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"for asdf in open('test.txt'):\n",
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" print asdf"
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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 2",
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"language": "python",
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"name": "python2"
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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": 2
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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": "ipython2",
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"version": "2.7.10"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 0
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}

‎.ipynb_checkpoints/Set-checkpoint.ipynb

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