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 ends with a space (before the quote)
Examples:
>>> input()
123
'123'
>>> input("Your name? ")
Your name? Dr. Simmons
'Dr. Simmons'
¶
>>> 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)
¶
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
¶
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)
firstname = input("what is your first name? ") print(firstname)
- what is inside the quotes?
- what is put into the lhs of the assignment?
Formatting 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,\"
quote -
sep=
separator (default: space) end=
ending (default: newline)
Examples¶
-use of escape sequences
print("one \t two \t three")
print("\"one\" \t \"two\"")
print("\\one \t \\two")
print ("one\ntwo\nthree")
- 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)
print("Today is Monday.")
print("Monday string beans.")
print("Today", "is", "Monday")
print("Today", "is", "Monday", sep="...")
print("Today is Monday, ", end="")
print("Monday string beans.")
print("Today", "is", "Monday", sep="? ", end="!!")
print("Monday string beans.")
¶
print("Today is Monday.")
print("Monday string beans.")
print("Today", "is", "Monday")
print("Today", "is", "Monday", sep="...")
print("Today is Monday, ", end="")
print("Monday string beans.")
print("Today", "is", "Monday", sep="? ", end="!!")
print("Monday string beans.")
- 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')
Types and operators: getting started¶
- Types of data: more to learn
- string
- "Sharon"
- integer
- 10
- float
- 15.356
- string
- 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
¶
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?