• A programming language we can use to communicate with the computer and solve problems
• We give the computer instructions that it will execute

• Python is a high level language that we (humans) can understand
– Other examples include C++ and Java
• A machine can only understand low level language
• So we process the high level to low level so the computer will understand!

• How do we translate high level languages to low level languages?
– We use interpreters and compilers!
– Interpreters process the program a little bit at a time and runs it
– Compilers translate everything before running it

• Program – a file of code that may contain functions
• Script – a short code that we can run in a command line
• Variable – names we assign the values to, allowing us to reuse them later on
– For example: x = 1 or msg = “Hello world!”
– Variables can be changed throughout a program
– For example: x = 1, x = x + 1

• Comments – notes ignored by the computer
– For example: x + y # variables store user input
• Operators – mathematical symbols
– +, -, *, /, ** (exponents), == (equality)

• Keyword – words with meaning/purpose in Python
– For example: “and”, “print”, “if”
• Expression – statements that produce values
– 3 + 5, “Hello world!”
• Error – program has a problem in the command area
• Instance – one run-through of a program

• A REQUIREMENT IN PYTHON!
• Indenting specifies the “scope” of different chunks of your code
– Everything indented after a first, unindented line
“belongs” to that line!

• Python is case sensitive
– A function called “first” is different than a function called “FIRST” or
“First” or “fiRSt”
• Python doesn’t like spaces or punctuation marks
– You can’t name your function “spam Five” or “spam.Five”
– You could, however, name your function“spamFive” or “spam_Five”
• Some words in Python can’t be used as names
– Keywords can never be used as function/variable names
– Check the colors of the words! Purple and orange are KEYWORDS!

• We had an argument passed into our function!
• The argument is known as a parameter
• Example def add(a, b): print(“This is a + b: “, a+b)
• a and b are the parameters

• Numeric
– Integers (5, 2, -1)
– Floating Point Numbers (0.2, 3.14159, 28.92)
• Non-numeric
– String (text), lists, dictionaries, etc
– Basically anything you can’t add up using a simple plus sign (+)

• You can format outputting variables you’ve already defined x = 42 print “The value of x is”, x, “.”
• What does this print out?

• The output is
– The value of x is 42.
• The bottom will cause an error.
x = 42 print “$” + x
• We can’t combine string and numbers. So what do we do?

• We can make our numerical variable a string!
x = 42 print “$” + str(x)
• This will print out $42

• Variables can hold all kind of values, including strings, numbers, and user input
• To assign a string value to a variable, you have to wrap the string in quotes firstName = “Jessi” lastName = “Cheung” mathProblem = “5 + 5” print lastName , “,”, firstName, “;”, mathProblem
• What will this print?

• The output is: Cheung, Jessi; 5 + 5
• Variables can also be assigned new values that are relative to their old values total = 10 print “Original total:”, total total = total + 4 print “New total:”, total
• What does this print?

• The output is
Original total: 10
New total: 14
• Remember: a variable has to be defined on a previous line before it can be used on the right-hand side of an equation
ABC = ABC + 4 print “ABC:”, ABC
• ERROR. There was no mention of the value of “ABC” before the line trying to redefine it.

• Try typing the following code in your program area and see what comes out!
def main(): a = 12 b = 2 c = 16 d = 3 e = 2.5
print “The value of a is”, a print (a / b) * 5 print a + b * d print (a + b) * d print b ** d print c – e a = a + b print “The value of a is”, a

• Is this what you got?
the value of a is 12
30
18
42
8
13.5
the value of a is 14

• Write a program that takes in a Celsius temperature (celsius) and returns the temperature in Fahrenheit
– Hint: To get Fahrenheit, multiply the Celsius by
(9.0/5.0) and add 32

• Sometimes, instead of passing in an argument as a parameter, we can have the computer ask us what we want!

name = requestString("Enter your name:") print name first pops up a dialog box (where you can enter a name, say ‘John Doe’): then outputs
John Doe

• Let’s try it with numbers!
def requestNumber(): num = input(“Enter a number:”) print “Your number is:”, num print “Your number squared:”, num*num

• What if you tried inserting a string into… def requestNumber(): num = input(“Enter a number:”) print “Your number is:”, num
• If you type hello , there will be an error. If you type
“hello” , it will work
• This is where raw_input comes into play!

• raw_input will take exactly what you type and make it into a string def requestName(): name = raw_input (“Enter your name:”) print name, “is awesome!”
• Try typing in a number!

• Let’s write a program that will calculate the area and the circumference of a circle!
• Open a new window (File/New Window)!
• At the top of your (blank) file, write the following:
# file name: circle.py
# author: Jessi Cheung
# description: a program to calculate the area and the circumference of a circle
• Save the program as circle.py

• Let’s define this program as main.
def main():
• Your turn!
– Use input to ask the user for the radius!

• We now have (besides our heading) def main(): radius = input(“What is the radius? “)
• Now let’s start the calculations!
– Circumference of a circle: Pi (3.14) times (radius times two)
– Area of a circle: Pi (3.14) times (radius squared)

• We now have (besides our heading) def main(): radius = input(“What is the radius? “) circumference = 3.14 * (2 * radius) area = 3.14 * (radius * radius)

• Now for the finishing touches!
• Let’s print out the output so we can see it!

def main(): radius = input(“What is the radius? “) circumference = 3.14 * (2 * radius) area = 3.14 * (radius * radius) print “The radius of our circle is”, radius print “The circumference of our circle is”, circumference print “The area of our circle is”, area

• Once you save your program, press F5 on your keyboard
• Nothing happens?!

• You must call your program!
• Call using main()

• Another way you could run the program…

• Also known as the “definite loop” – we know exactly how many times the loop will happen!
• Allows you to specify a list of items (numbers, words, letters, etc.) and specify actions to be performed on each one
• The official syntax for the for loop is: for <var> in <sequence>:
<body>

• You are working at an animal shelter, and you’re asked to take a group of kittens and bathe, dry, and feed each one individually

• Using a for-loop type notation, your instructions would look like this:
Kittens = [kitty #1, kitty #2, kitty #3, ...] for kitty in Kittens: bathe kitty dry kitty feed kitty

• See what happens when you put in this: p hrase = “Hello world!” for letter in phrase: print “the next letter is:”, letter

• The output!
the next letter is: H the next letter is: e the next letter is: l the next letter is: l the next letter is: o the next letter is: the next letter is: w the next letter is: o the next letter is: r the next letter is: l the next letter is: d the next letter is: !

• Python went through the string one character at a time, treating the string like a sequence
• That means that the string can be split into its components (the characters)

• When you’re using a for loop, sometimes you might want to keep a running total of numbers you’re calculating, or recombine bits of a string

• Steps:
1.
Define a variable for the first time before the loop starts
2.
Redefine it as itself plus some operation in the body of the for loop total = 0 for num in [1,2,4,10,20]: total = total + num print “Total:”, total
• This will give the output
Total: 37

• What is the point of accumulator variables?
– Counting
– Keeping score
– Debugging

• Equals: ==
• Does not equal: !=
• Try this: x = 1 if (x != 2): print “Artemis rocks”

• Go to: wiki.python.org/moin/BeginnersGuide