Your first Python statement

• print() function

Documentation:

• https://docs.python.org/3/library/functions.html#print

Examples:

>>> print("Hello!")
Hello!

Your second Python statement

• input() function

Documentation:

• https://docs.python.org/3/library/functions.html#input
• Prompts usually end with a space (before the quote)

Examples:

>>> input()
123
'123'

>>> input("Your name? ")
Your name? Dr. Simmons
'Dr. Simmons'

Beginning facts

• Python interpreter: executes code written in Python

• Interactive interpreter: allows users to execute on line at a time

• prompt >>> is the interactive interpreter

• Code, statement, program

• comments # or """

• output
  print("Hello, World!")

  • inside the quotes is a string literal

Comments

"""  All of this is a comment and is not considered code. 
You can have multiple lines like this """ 
print("this code is executed")

# this prints my name
print("my name is Dr. Simmons")

• notice the newline when you execute these lines of code

Variables (Identifiers)

• start with a lowercase letter
• _ to separate words
• avoid keywords/reserved words
• use meaningful identifiers
• variable is a name associate with a place to hold data
• e.g., number_cats, cat_name, total

 number_cats = 2
 univ_name = "JMU" #string literal

Assignment

• assignment operator
• creates a variable or changes the value of an existing variable
• lhs and rhs
• which variable's value was changed?
• output the value of a variable

Example:

value = 0.0
NICKEL = 0.05  # constant
number_nickels = 15
value = number_nickels * NICKEL  #rhs is an expression
print("the value is", value)

Expressions

weekly_rate = 0
payrate = 25
hours_per_week = 20
weekly_rate = payrate * hours_per_week

Input

• input() reads text entered by the user
• excecution is suspended until the user enters data and presses return
• the input obtained from input() is a string (series of characters)

    lastname = input("what is your first name? ")
    print(lastname)

• what is inside the quotes?
• what is put into the lhs of the assignment?

More about output ...

• Strings may use single quotes (') or double quotes (")
  • Single quotes are the default, but I tend to use double
• Escape sequences: \n newline, \t tab, \\ backslash
• print text on the same row

    print("hello",  end= " ")
    print("Sharon")

• multiple items in a print statement

    year = 2023
    month = "August"
    print("the year is", year, "and the month is", month)

• calculations in a print statement

    print("next year will be", year+1)

• another example

print('She said, "Hello!"\nI was shocked!')

Output continued

-newline

    print('hello')
    print('world')

• what happens?
• how can you get the equivalnet output with one statement?

Types and operators: getting started

• Types of data: more to learn
  • string
    • "Sharon"
  • integer
    • 10
  • float
    • 15.356
• Operators for data: more to learn
  • add +
  • substract -
  • multiply *
  • divison /

Input, strings, int() and math operators

• try this:

hours = int(input("How many hours did you work this week? "))
days = int(input("How many days did work this week? "))
print("You worked an average per day of ", hours/days, "hours")

• Try the following, then fix the errors.

temperature = input("enter the current tempature: ")
night_temp = temperature - 20

• Try the following:

cats = input("How many cats do have? ")
dogs = input("How many dogs do have? ")
total = cats + dogs
print(total)

• what happened?

Errors

• syntax error
• runtime error
• logic error
  Examples:

print('She said, "Hello!"\nI was shocked!)
total = 10
print(total+1)

name = "Sharon"
age = int(name)

height = 25
width = 16
area = width + height

Character and Escape Sequences

• Unicode
  • example D is 48 (see chart)
  • D is character
  • string is a series of characters

print(ord('D'))
print(chr(100))

• Escape sequence
  • backslash then a character
  • special meaning

    print('Dr. Simmons\' cats are named Ricky and Lucy')

Example Python Program

””” 
Application that converts inches to centimeters.
”””
inch = 0
cent = 0.0
CENT_PER_INCH = 2.54
# Prompt the user and get the value.
inch = int(input("How many inches?"))
# Convert and output the result.
cent = inch * CENT_PER_INCH
print(inch, "in =", cent, "cm")

A few terms learned so far ...

• Integrated Development Environment IDE: e.g., Thonny
• identifier
• statement
• expression
• assignment
• input
• output
• processing
• comments
• anything else?

• f-strings f"{...}" (f = formatted string literal)