Python! An Introduction
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![Page 25: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/25.jpg)
Variables
![Page 26: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/26.jpg)
VariablesCalculate a value:
>>> 12 * 12144
How can you save that value, 144?
Assign a name to a value:
>>> donuts = 12 * 12>>> color = “yellow”
A variable is a way to store a value.
![Page 27: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/27.jpg)
>>> donuts = 12 * 12>>> color = “yellow”
Assign a new value:
>>> color = “red” >>> donuts = 143
>>> color = “fish” >>> color = 12>>> color12
Variables
![Page 28: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/28.jpg)
★ Calculate once, keep the result to use later
★ Keep the name, change the value
Some other things we can do with variables:
>>> fruit = “watermelon”>>> print fruit[2]>>> number = 3>>> print fruit[number-2]
Variables
![Page 29: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/29.jpg)
Converting variables:
Turn a string into a number (use int or float).
>>> pets = '4'>>> num_pets = int(pets)
Turn a number into a string:
>>> str_pets = str(num_pets)
Variables
![Page 30: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/30.jpg)
>>> name = “Barbara”>>> color = “blue”>>> print “My name is”, name, “and my favorite color is”, color
>>> name = “Sara”>>> color = “purple”>>> print “My name is”, name, “and my favorite color is”, color
Variables Practice 1
![Page 31: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/31.jpg)
>>> print “My name is”, name, “and my favorite color is”, color
Output:My name is Barbara and my favorite color is blue
My name is Sara and my favorite color is purple
Variables Practice 1: Answers
![Page 32: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/32.jpg)
>>> name = “Andrew”
>>> age = 30
>>> dog_year_length = 7
>>> dog_years = age * dog_year_length
>>> print name, “is”, dog_years, “in dog years!”
Variables Practice 2
![Page 33: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/33.jpg)
>>> print name, “is”, dog_years, “in dog years!”
Andrew is 210 in dog years!
Variables Practice 2: Answers
![Page 34: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/34.jpg)
Use decimal numbers if needed for precision:
>>> age = 32>>> decade = 10>>> print “I’ve lived for”, age/decade, “decades.”
>>> decade = 10.0>>> print “I’ve lived for”, age/decade, “decades.”
Variables Practice 3
![Page 35: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/35.jpg)
>>> print “I’ve lived for”, age/decade, “decades.”
I’ve lived for 3 decades.
I’ve lived for 3.2 decades.
Variables Practice 3: Answers
![Page 36: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/36.jpg)
Errors
![Page 37: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/37.jpg)
>>> “friend” * 5‘friendfriendfriendfriendfriend’
>>> “friend” + 5Error
Errors
Traceback (most recent call last): File "<stdin>", line 1, in <module>TypeError: cannot concatenate 'str' and 'int' objects
Do you remember what ‘concatenate’ means?What do you think ‘str’ and ‘int’ mean?
![Page 38: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/38.jpg)
Traceback (most recent call last): File "<stdin>", line 1, in <module>TypeError: cannot concatenate 'str' and 'int' objects ^ ^ ^ ^
• Strings: ‘str’• Integers: ‘int’• Both are objects• Python cannot concatenate objects of different types
Errors
![Page 39: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/39.jpg)
Here’s how we would fix that error:
>>> “friend” + 5Error
Concatenation won’t work.
Let’s use the print command for display:
>>> print “friend“, 5friend 5
No concatenation, no problem!
Errors
![Page 40: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/40.jpg)
1. Store your name, height and favorite color in variables. Print that information in a sentence.
2. Calculate the number of 2-week disposable contact packs you need in a year and store that value in a variable. Print, in sentence form, the number of disposable contact packs you need to buy to be stocked for two years.
3. Calculate how many seconds all attendees will spend in this workshop and store it in a variable. Print the answer as a sentence.
4. Calculate the number of donuts made in a week if 15 dozen are made each day. Print, in sentence form, the number of donuts 100 people would have to eat in order to finish them all.
Exercise Set 1
![Page 41: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/41.jpg)
Store your name, height and favorite color in variables. Print that information in a sentence.
>>> name = “Barbara”>>> height = “67”>>> color = “blue”>>> print name, “is”, height, “inches tall and loves”, color, “!”
Barbara is 67 inches tall and loves blue!
Exercise Set 1: Review
![Page 42: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/42.jpg)
Calculate the number of 2-week disposable contact packs you need in a year and store that value in a variable.
>>> contact_packs = 52 / 2
Print out, in sentence form, the number of disposable contact packs you need to buy to be stocked for two years.
>>> print “I will need to buy”, contact_packs, “contact packs this year.”
I will need to buy 26 contact packs this year.
Exercise Set 1: Review
![Page 43: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/43.jpg)
Calculate how many seconds all attendees will spend in this workshop.
Store that value in a variable.
>>> seconds = 60 * 60 * 6 * 32
Print the answer in a sentence.
>>> print “Attendees will spend a total of”, seconds, “seconds in this workshop.”
Attendees will spend a total of 1152000 seconds in this workshop.
Exercise Set 1: Review
![Page 44: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/44.jpg)
Calculate the number of donuts made in a week if 15 dozen are made each day.
>>> number_of_donuts = 15 * 12 * 7
Print, in sentence form, the number of donuts 100 people would have to eat in order to finish them all.
>>> print “Each person will eat”, number_of_donuts / 100.0, “donuts.”
Each person will eat 12.6 donuts.
Exercise Set 1: Review
![Page 45: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/45.jpg)
Types of data
![Page 46: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/46.jpg)
Three types of data we already know about:
“Hi!” string 27 integer
15.238 float
Python can tell us about types using the type() function:
>>> type(“Hi!”)<type ‘str’>
Can you get Python to output int and float types?
Data types
![Page 47: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/47.jpg)
Data type: Lists
![Page 48: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/48.jpg)
List: a sequence of objects
>>> fruit = [“apple”, “banana”, “grape”]>>> numbers = [3, 17, -4, 8.8, 1]>>> things = [“shoes”, 85, 8.8, “ball”]
Guess what these will output:
>>> type(fruit)>>> type(numbers)>>> type(things)
Lists
![Page 49: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/49.jpg)
Guess what these will output:
>>> type(fruit)<type ‘list’>
>>> type(numbers)<type ‘list’>
>>> type(things) <type ‘list’>
Lists
![Page 50: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/50.jpg)
Lists have indexes just like strings.
>>> fruit[‘apple’, ‘banana’, ‘grape’]
>>> print fruit[0]‘apple’
How would you use type() to verify the type of each element in the list?
Lists
![Page 51: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/51.jpg)
Lists
Make a list of the four Beatles.
Use an index to print your favorite one’s name.
![Page 52: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/52.jpg)
Make a list of the four Beatles.
>>> beatles = [‘John’, ‘Paul’, ‘George’, ‘Ringo’]
Use an index to print your favorite one’s name.
>>> print beatles[2]
Lists
![Page 53: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/53.jpg)
Read about other ways of managing sequences of data:
dictionaries - http://bit.ly/U3J19ctuples - http://bit.ly/1068Drksets - http://bit.ly/ZoK9qK
Homework
![Page 54: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/54.jpg)
Data type: Booleans
![Page 55: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/55.jpg)
A boolean value can be: True or False
Is 1 equal to 1?
>>> 1 == 1True
Is 15 less than 5?
>>> 15 < 5False
Booleans
![Page 56: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/56.jpg)
What happens when we type Boolean values in the interpreter?
>>> True>>> False
When the words ‘True’ and ‘False’ begin with capital letters, Python knows to treat them like Booleans and not strings or integers.
>>> true>>> false>>> type(True)>>> type(“True”)
Booleans
![Page 57: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/57.jpg)
andBoth sides of the expression must be True.
>>> True and True>>> 1 == 1 and 2 == 2>>> True and False
Booleans: Comparisons
orOnly one side of the expression needs to be True.
>>> True or True>>> True or False>>> 1 == 1 or 2 != 2
![Page 58: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/58.jpg)
not
When you use not:- something True becomes False- something False becomes True
>>> not 1 == 1>>> not True
Booleans: Reverse
![Page 59: Python! An Introduction](https://reader034.fdocuments.in/reader034/viewer/2022052601/558def621a28ab357e8b46d5/html5/thumbnails/59.jpg)
Try some of these expressions in your interpreter:
Booleans: Practice
>>> True and True>>> False and True>>> 1 == 1 and 2 == 1>>>"test" == "test">>> 1 == 1 or 2 != 1>>> False and False
>>> True and 1 == 1>>> False and 0 != 0>>> True or 1 == 1>>>"test" == "testing">>> 1 != 0 and 2 == 1>>> False or False
For practice later:http://bit.ly/boolean-practice
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Logic
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if Statements
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if StatementsMaking decisions:
"If you're not busy, let's eat lunch now.""If the trash is full, go empty it."
If a condition is met, perform the action that follows:
>>> name = "Jess">>> if name == "Jess":... print "Hi Jess!"
Hi Jesse!
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Adding more choices:
"If you're not busy, let's eat lunch now. Or else we can eat in an hour."
"If there's mint ice cream, I'll have a scoop. Or else I'll take butter pecan."
The else clause:
>>> if name == "Jess":... print "Hi Jess!"... else:... print “Impostor!”
if Statements
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Including many options:
"If you're not busy, let's eat lunch now. Or else if Bob is free I will eat with Bob. Or else if Judy's around we'll grab a bite. Or else we can eat in an hour."
The elif clause:
>>> if name == "Jess":... print "Hi Jess!"... elif name == “Sara”:... print “Hi Sara!” ... else:... print “Who are you?!?”
if Statements
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if Statements: PracticeWrite an if statement that prints "Yay!" if thevariable called color is equal to "yellow".
Add an elif clause and an else clause to print two different messages under other circumstances.
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Write an if statement that prints "Yay!" if thevariable called color is equal to "yellow".
Add an elif clause and an else clause to print two different messages under other circumstances.
>>> color = "blue">>> if color == "yellow":... print "Yay!"... elif color == "purple":... print "Try again" ... else:... print "We want yellow!"
if Statements: Practice
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Loops
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Loops are chunks of code that repeat a task over and over again.
★Counting loops repeat a certain number of times.
★Conditional loops keep going until a certain thing happens (or as long as some condition is True).
Loops
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Counting loops repeat a certain number of times.
>>> for mynum in [1, 2, 3, 4, 5]:... print “Hello”, mynum
Hello 1Hello 2Hello 3Hello 4Hello 5
The for keyword is used to create this kind of loop, so it is usually just called a for loop.
Loops
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Conditional loops repeat until something happens.
>>> count = 0>>> while (count < 4):... print 'The count is:', count... count = count + 1
The count is: 0The count is: 1The count is: 2The count is: 3
The while keyword is used to create this kind of loop, so it is usually just called a while loop.
Loops
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Loops: Practice
Create a list of some of your classmates’ names
Loop over the list and say hello to each person.
Remember: The second line should be indented 4 spaces.
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Loops: Practice
Create a list of some of your classmates’ names
>>> names = [“Barbara”, “Jay”, “Maddy”]
Loop over the list and say hello to each person.
>>> for person in names:... print “Hello”, person
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Functions
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Remember our PB&J example?
1. Get bread2. Get knife4. Open PB3. Put PB on knife4. Spread PB on bread ...
1. Make PB&J
Functions
Which is easier?:
Functions are a way to group instructions.
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What it's like in our minds:
“Make a peanut butter and jelly sandwich.”
In Python, it could be expressed as:
make_pbj(bread, pb, jam, knife) ^ ^ ^ ^ ^ function name function parameters
Functions
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Let's create a function in the interpreter:
>>> def say_hello(myname): ... print ‘Hello’, myname
Remember: The second line should be indented 4 spaces.
Functions
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def is the keyword we always use to define a function.
‘myname’ is a parameter.
>>> def say_hello(myname):... print ‘Hello’, myname
Functions
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Now we'll call the function:
>>> say_hello("Katie")Hello, Katie
>>> say_hello("Barbara")Hello, Barbara
Use your new function to say hello to some of your classmates!
Functions
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1. Work alone or with a neighbor to create a function that doubles a number and prints it out.
Functions: Practice
2. Work alone or with a neighbor to create a function that takes two numbers, multiplies them together, and prints out the result.
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1. Work alone or with a neighbor to create a function that doubles a number and prints it out.
>>> def double_number(number):... print number * 2
>>> double_number(14)28
Functions: Practice
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2. Work alone or with a neighbor to create a function that takes two numbers, multiplies them together, and prints out the result.
>>> def multiply(num1, num2):... print num1 * num2
>>> multiply(4, 5)20
Functions: Practice
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print displays something to the screen. But what if you want to save the value that results from a calculation, like your doubled number?
Functions: Output
>>> def double_number(number):... print number * 2
>>> new_number = double_number(12)24
>>> new_number>>>
>>> new_number = double_number(12)24
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>>> def double_number(number):... return number * 2
>>> new_number = double_number(12)24
>>> new_number24
Functions: Output
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Rules:
★ Functions are defined using def.
★ Functions are called using parentheses.
★ Functions take input and can return output.
★ print displays information, but does not give a value
★ return gives a value to the caller (you!)
Functions
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★ Comments are used as reminders to programmers.
★ Computers ignore comments, but they are useful to humans.
★ Use # to start comments
>>> def double_number(number):... # Here’s where we double the number:... return number * 2
>>> new_number = double_number(12)24
>>> # You can also have a comment by itself
Comments
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Modules
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Modules
A module is a block of code that can be combined with other blocks to build a program.
You can use different combinations of modules to do different jobs, just like you can combine the same LEGO blocks in many different ways.
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ModulesThere are lots of modules that are a part of thePython Standard Library
How to use a module:
>>> import random>>> print random.randint(1, 100)
>>> import time>>> time.time()
>>> import calendar>>> calendar.prmonth(2013, 3)
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ModulesA few more examples:
>>> import os>>> for file in os.listdir(“~/Desktop”):... print file
>>> import urllib>>> myurl = urllib.urlopen('http://www.python.org')>>> print myurl.read()
You can find out about other modules at: http://docs.python.org
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Objects
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Objects
Real objects in the real world have:
• things that you can do to them (actions)
• things that describe them (attributes or properties)
In Python:
• “things you can do” to an object are called methods
• “things that describe” an object are called attributes
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ObjectsThis ball object might have these attributes:
myBall.colormyBall.sizemyBall.weight
You can display them:
print myBall.sizeYou can assign values to them:
myBall.color = ‘green’You can assign them to attributes in other objects:
anotherBall.color = myBall.color
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ObjectsThe ball object might have these methods:
ball.kick()ball.throw()ball.inflate()
Methods are the things you can dowith an object.
Methods are chunks of code - functions - that are included inside the object.
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ObjectsIn Python the description or blueprint of an object is called a class.
class Ball: color = ‘red’ size = ‘small’ direction = ‘’ def bounce(self): if self.direction == ‘down’: self.direction == ‘up’
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ObjectsCreating an instance of an object:
>>> myBall = Ball()
Give this instance some attributes:
>>> myBall.direction = “down”>>> myBall.color = “blue”>>> myBall.size = “small”
Now let’s try out one of the methods:
>>> myBall.bounce()
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Practice Exercises
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Practice Exercises
http://codingbat.com/python
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Some Simple Programs
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Some Simple ProgramsLog in to Appsoma: https://appsoma.com/codeClick on the ‘Code’ tab and type the following:
def greeting(): your_name = raw_input('Type your name:') if your_name == 'Matt': print "Hi Matt!" else: print "Hello", your_name
greeting()
Click on the ‘Save As’ button and save the file as name.pyClick on the ‘Run’ button and follow the prompt.
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Some Simple ProgramsClose both open tabs, then click on the ‘New’ button and type this:
secret_number = 7
guess = input("What’s the secret number? ")
if secret_number == guess: print "Yay! You got it."else: print "No, that's not it."
Save the file as guess.py and click on the ‘Run’ button.
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Some Simple ProgramsClose the tab on the right, then make these changes to the game and save your file. When you finish, click the ‘Run’ button again:
from random import randint
secret_number = randint(1, 10)
while True: guess = input("What’s the secret number? ") if secret_number == guess: print "Yay! You got it." break else: print "No, that's not it."
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Some Simple ProgramsClose the tab on the right, then make these changes to the game and save your file. When you finish, click the ‘Run’ button again:
from random import choice
secret_number = choice(range(1, 20))
while True: guess = input("What’s the secret number? ") if secret_number == guess: print "Yay! You got it." break elif secret_number > guess: print "No, that's too low." else: print "No, that's too high."
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Congratulations!You’re now a Pythonista!
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Let’s go back to this quiz: http://pyladi.es/atx-quiz
Remember this?
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Find hack nights, local user groups, keep practicing!
PyLadies Austinhttp://www.meetup.com/PyLadies-ATX/
Austin Web Pythonhttp://www.meetup.com/austinwebpythonusergroup/
Python Web Houstonhttp://www.meetup.com/python-web-houston/
If there’s no user group in your area, start your own!
What do to next:
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Where to learn more:Self-paced tutorialshttp://learnpythonthehardway.org/book/http://www.codecademy.com/tracks/pythonhttps://www.khanacademy.org/cs/tutorials/programming-basics
Online Classeshttps://www.udacity.com/course/cs101https://www.udacity.com/course/cs253http::/www.coursera.org(add Google Developer Python course)
Learn more about lists and zero indexinghttps://www.khanacademy.org/science/computer-science/v/python-listshttp://en.wikipedia.org/wiki/Zero-based_numbering