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Michelle edited this page Jun 6, 2016 · 1 revision

Introduction to Python for Academic Researchers



GCDRI June 7, 2016 #GCDRI

Michelle McSweeney @MMcSweeney7

First Half Lesson Plan:

  • Overview
  • Variables & Types
  • Conditionals

~ Break ~ (approximately)

Second Half Lesson Plan

  • Loops
  • Functions
  • Psuedocode
  • Libraries

Python is a Language that supports many Packages

Packages

  • NLTK (Natural Language Toolkit) for Text Analysis
  • Pandas for Data Analysis and Modeling (DataFrames)
  • Numpy for High Level Mathematical Functions
  • MatPlotLib for Making Graphs and Charts

How do I know which one to use?

The Internet

Stack Overflow

Read the docs

Others doing similar work

Variables and Types

Variables are like a container for holding something

This can be helpful because:

  • sometimes things are long:

    • my_file = open('/Users/michellejohnson/Documents/Spanish_English_BYTs.csv', 'r')

  • sometimes you need a place to put something:

    • love_den = love_words/all_words

  • sometimes you will just need a variable!

Interactive Time!

  • Open Anaconda (green guitar pick)
  • Launch Notebook (will open in browser)
  • New (at top right hand side of page)

To run a cell hit:

'Shift' + 'Enter'

#setting my first variable

x = 8
y = 2
x+y
z = x-y
print(z)

Some rules about variables

  • NO SPACES
  • Must be unique (unless you're overwriting something)
  • Cannot be a command Python already uses, or is already used by a package (we'll come back)
a = 3
b = 4
a = b
print('a is', a)
print('b is', b)

Types

  • Numbers
    • Integers
    • Floats

Types

  • Strings " " or ' ' (this is so you can use apostrophes or quotes inside a string)
    • usually words, always things Python can't "evaluate"
    • 'love'
    • 'Hello GCDI'

Types

  • Lists [ ]
    • just like a shopping list
    • ['apples', 'bananas', 'kiwi']
    • [100, 200, 300]

Types

  • Dictionaries { }
    • key:value pair
    • Keys are always unique - like your house key!
    • Values are not always unique...
    • Useful for counting instances of things
      • Let's say you are counting words:
      • {'a':200, 'the': 500, 'at': 200}

Types

List versus Dictionary

  • List is ordered, Dictionary is not
  • Lists allow look up by an index
  • Dictionaries allow look up by a key More to come

Types

We are not covering these here

  • Sets
    • Tuples(things grouped together, an unchangeable list)
    • Arrays (in Python, just use a list
  • Texts (special (usually package-specific) type for words)
  • DataFrame (specific to Pandas, like a spreadsheet or matrix)

Type Examples

Integers

n = 5
type(n)
int

Type Examples

Floats

m = 5.1
type(m)
float

Type Examples

Strings

str1 = 'Hello'
str2 = 'GCDRI'
print (str1)
print(str1, str2)
str3 = str1 + str2
print(str3)
str4 = str1 + ' ' + str2
print(str4)

Type Examples

Lists

Just like a shopping list

my_list = ['apples', 'spinach', 'tofu']
print(my_list)
my_list.append('rice')
print(my_list)
my_list[1]

Type Examples

Dictionaries

my_dict = {'steak': 2, 'potatoes': 5, 'salad': 6}
print(my_dict)
my_dict.items()
my_dict.keys()
my_dict.values()
my_dict['steak']
my_dict[2]

Why did that break?

Keys are unique

Values are not unique

Can only "call" or add items by their key

my_dict['pie'] = 4
print(my_dict)

Conditionals

aka "If-then statements"

Some style issues: * if item in my_list: * if a == b: * if a > b: * if a >= b:

if students > teachers:
    print('Classroom')
if students < teachers:
    print('Conference')
if teachers == students:
    print('Private School')
students = 60
teachers = 2

Let's check on our original list (my_list should still be an active variable in your program)

print(my_list)
if 'tofu' in my_list:
    print('Dinner time!')
else:
    print('You forgot my tofu!')

Three pieces of vocabulary for conditionals if _______: elif _________: else:

if 'bagel' in my_list:
    print('Too many carbs')
elif 'tomatoe' in my_list:
    print('So healthy!')

What happened? Why didn't anything print?

What happens without the 'else' statement?

Challenge Question, this time, we'll play a game with Python. We need another tool: input *input is a way for Python to get information from a user.

win = input('Pick the winning number: ')
guess = input('Player2, guess the number: ')
if win < guess:
    print('too high')
elif win == guess:
    print('you win!')
else:
    print('too low')

For Loops

#First, let's remember what was in my_list
print(my_list)
for item in my_list:
    print("I'm gonna eat", item)

Now let's look at some numbers, we will put them in a new list

there's a better way to do this, look up the function, range, if you regularly use lists of numbers in order

num_list = [1,2,3,4,5]
for digit in num_list:
    print(digit)
    
for digit in num_list:
    digit+=1

print(digit)

What does += do

Why did it only print 6??

new_numb = []

for digit in num_list:
    new_dig = digit + 3
    new_numb.append(new_dig)

print(new_numb)

In regular language, what happened here?

Advanced For-Loops: Dealing with Dictionaries

for item in my_dict:
    print("I'm gonna eat", item)

Why didn't it tell us how many of each? What did it return?'

for item in my_dict.items():
    print("I'm gonna eat", item)

Combining For-Loops and If-Statements!!

fav_foods = ['watermelon', 'tofu', 'spinach', 'coffee']
for food in fav_foods:
    if food in my_list:
        print('Yum', food)
    else:
        print('No', food, '?')

Now let's try it the other way to really get a sense of what is happening

for food in my_list:
    if food in fav_foods:
        print('Yum', food)
    else:
        print('No', food, '?')

Functions!

Functions are little bits of code that you can use over and over again.

  • Python has some
  • You can write some yourself
  • You can import libraries of them
  • You can borrow them from your friends!

Functions are Fun!!

Some vocabulary:

def _______(argument): some things i do what I give back

The argument is what the function will need to do its job. It's usually the little piece of information that your function operates on.

#This function takes one argument and prints a greeting to the screen
#The argument is a string

def greet(name):
    print('Hello,', name)
    print('How are you?')
greet('Wanda')
greet('Floyd')

Now I want to greet both of them.

greet('Wanda', 'Floyd')

Why did that break?

Let's try again

greet('Wanda and Floyd')

Another Tool!

input() - a way to get information directly from your user

x = input('What is your favorite number? ')
print('My favorite number is', x)
What is your favorite number? 8
My fav number is 8

Let's write a program to tell people how to write a book.

Hint: This program will require using a Function!

Start with pseudocode

Wait! What's pseudocode???

Psuedocode is simplified code.

  • Articulate in words what you need the program to do

  • Identify what you want to give it

  • Identify what you expect to get back

  • Identify the major steps

  • Tackle each major step individually

    • Worry about other steps later
    • Write out in words every tiny step
    • Test to see if the major step worked
    • Repeat this step

  • Call your program

I want to write a program that gives people advice about how to write a book. This program gets information from the user and tells them what they should do.

  • Inputs: time & ideas
  • Consider relationship between time and ideas, decide what advice to give
  • Outputs: Advice

ideas = get number of ideas

time = get amount of time

Decide what advice to give:

  • if they have less time than ideas, they should make time.

  • if they have fewer ideas than time, they should get inspired.

  • if the two are equal, they will probably write a book.

#ideas = get number of ideas
all_ideas = input('How many ideas do you have? ')
#time = get amount of time
all_time = input('How much time do you have? ')
def book(ideas, time):
    print('How to write a book')
    #if they have less time than ideas, they should make time.
    if time < ideas:
        print('Make time!')
    #if they have more ideas than time, they should get inspired.
    elif time > ideas:
        print('Get inspired')
    #if the two are equal, they will probably write a book.
    elif time == ideas:
        print("Can't wait to read it!")
    else: 
        pass
#run program
book(all_ideas, all_time)
#ideas = get number of ideas
all_ideas = input('How many ideas do you have? ')
#time = get amount of time
all_time = input('How much time do you have? ')

def book(ideas, time):
    print('How to write a book')
    #if they have less time than ideas, they should make time.
    if time < ideas:
        print('Make time!')
    #if they have more ideas than time, they should get inspired.
    elif time > ideas:
        print('Get inspired')
    #if the two are equal, they will probably write a book.
    elif time == ideas:
        print("Can't wait to read it!")
    else: 
        pass
        
#run program
book(all_ideas, all_time)

Congratulations!!

You just wrote your first program!!

Now let's look at some built-in functions!

open( ) opens a file

read( ) reads the file

len( ) gets length of an object (i.e., string, list, dictionary, etc.)

Curious about all the built-in functions?

https://docs.python.org/3/library/functions.html

This is essentially what you are doing when you import a library.

Someone else already wrote all these little programs, and you are using them!

Three ways to import libraries:

  • import csv - 'import' is a command, 'csv' is a package

  • from csv import * - this says 'go to nltk and import everything' - save yourself and don't do this

  • from csv import register_dialect

OMG! What's the difference??

Something useful!!

Now let's read in a csv file!

import csv

f = open('/Users/michellejohnson/Desktop/pd_collections.csv', 'r')
my_file = csv.reader(f)

for row in my_file:
    print(len(row))

Now you are ready to specialize your programming skills through

  • Cleaning Data
  • Analyzing Text
  • Analyzing Numerical Data
  • Making charts and graphs
  • So much more!!

Now let's move to the Command Line!!

  1. open a Terminal Window

  2. Type the following command:

    $ python

  3. Now you are using Python (to run a line of code, just hit 'Enter' not 'Shift'+'Enter'

  4. Let's try it out with this simple program

    x = 'I love GCDI'

    len(x)



              


          



  
          

            


            
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