Python Basics (class slides)

CSc 110 Python Basics

Announcements

Did you set up your workspace?

  • Did you download Python 3?
  • Did you download VS Code (or PyCharm, or Mu)?
  • If not, that’s fine, you can use replit.com

What is a program?

The print function

  • What does the print function do?

The print function

  • print() sends characters (strings) to the standard output
  • By default, the standard output of a python program goes to the console.
print("some characters")
some characters


print('some characters')
some characters

String operations

String concatenation:

  • What will the standard output display when the code below is run?
print("hello" + "world")

String operations

In your groups, try the following operations:

  • String repetition: "abc" * 4
  • String concatenation with + and ,. What is the difference?
  • Combine both repetition and concatenation to print the following:
They sang AaAaAaAaAaAaAaAaAaAa

Multiple print statements

  • What will the standard output display when the code below is run?
print('Are')
print('You')
print('In')
print('College?')

Multiple print statements

  • By default, the print function sends the output cursor to the next line after printing
print('Are', end = ' ')
print('You', end = ' ')
print('In', end = ' ')
print('College?', end = ' ')
Are You In College?

What other characters can you use for values for the end parameter?

Dealing with special characters

Write a simple program that prints the following output to the python console:


   He said, "What's up?" 
   Joe's friend didn't reply.

Attendance

  • As a group, submit your answer to Gradescope Attendence January 12 (Friday)

Variables

Variables and assignment

  • Variables are names in a program that represent a stored value
  • We can assign names to particular values in our program
  • When we give a value a name, or update the value stored in a variable, this is called assigning a variable

Demonstration of variable assignment

Variable assignment does not produce any output to the console. Run the following code:

first_name = "Mary"
family_name = "Silva"

How would we print these variables?

Statements (vs expressions)

  • Expressions represent values or the computation of values
  • Statements represent executable steps in a program.
  • Statements often include expressions

Here’s a statement that invokes the print function with the expression 3 + 4 as an argument.

print(3 + 4)

Basic Types

  • string: "hello" or 'hello'
  • integer: 3
  • float: 3.14
  • bool: True or False

Use the function type() with each literal type.

Operations

Try the following operators with the different types in python:


   +
   -
   *
   /
   //
   %
   **

Operations and Variable Assignments

Variable assignments are not like math — they can appear in equations that make no mathematical sense.


x = 5
print(x)
x = x + 2
print(x)


x = x + 2 means “take the current value of x, add it with 2, and assign the resulting value (7) to x as its new value.”

Comments

Computer program can include comments, which are simply text that is meant to be read, but not executed.


# assign a radius value
radius = 3
# compute the area of a circle
area = 3.1415 * radius ** 2


The purpose of comments is to “document” the program so that subsequent readers can more easily understand it, or learn things about it (e.g., its original author).