GWU ISTM6200 Lecture 2: Python Variables, Expressions, and Statements

This document presents lecture notes from ISTM6200, focusing on fundamental Python programming concepts. It covers variable naming rules, data types (numbers, strings, lists, tuples, and dictionaries), and type conversions. The lecture explains expressions (combinations of constants, variables, and operators), and various operators (arithmetic, comparison, and logical), including operator precedence. It also discusses assignment statements, assignment operators, and multiple assignments. Furthermore, the lecture introduces built-in functions like `print()` and `input()`, providing examples and exercises. The document emphasizes the importance of understanding these concepts for effective Python programming and provides resources for further learning.

Prof. Wei Chen ([e-mail])
Dep. of Information Systems & Technology Management
May 27, 2021
Lecture 2: Variables, Expressions, Statements

ISTM6200 / Summer 2021
Class 2: Overview
Learning Objectives:
• Be familiar with variable naming rules
• Be familiar with the basic data types
• Be able to convert data types when necessary
• Understand basic expressions and statements
Today’s Agenda:
• Recap
• Variables and Data Types
• Expressions and Statements
• Basic Built-in Functions

ISTM6200 / Summer 2021
Recap: Python as a Language
• Python is an incredibly efficient language: your
program will do more in fewer lines of code than
many other languages would require
• We use Python for many purposes:
▪ make games
▪ build web applications
▪ solve business problems (data problems)
▪ …
• The Python community: ask advice from others
who have already solved similar problems

ISTM6200 / Summer 2021
Recap: Jupyter Notebook
Create a new python file

ISTM6200 / Summer 2021
Recap: Jupyter Notebook

ISTM6200 / Summer 2021
Variables
• A variable is a name that represents a value
stored in the computer’s memory, i.e., a storage
space with a symbolic name.
X
• Variables vs. Constants: Fixed values (e.g.,
numbers, letters, strings) are called ``constant’’
since their values do not change.
• The “content” of a variable can be changed:
Example: x = 10
x = “Hello”
print(“The value of x is ”, x)

ISTM6200 / Summer 2021
Variables (Cont.)
• A variable is created the first time you assign it a value
Variables must be created before they are used.
Assignment statement: assigns a value to a variable.
Syntax: Variable Name = Variable Value.
Example:
In [1]: x = 5
x
Out[1]: 5
In [2]: Class = “ISTM 6200”
Class
Out[2]: ‘ISTM 6200’

ISTM6200 / Summer 2021
Naming Conventions
• Names can consist letters, numbers and the underscore
character.
• Names must begin with a letter, or underscore
character.
• Names cannot contain spaces.
• Names are case sensitive, e.g., bob ≠ Bob ≠ BOB
• We cannot use one of Python’s keywords as variable
name!
• Recommended practices when naming variables:
• Meaningful
• Succinct
• Lowercase, concatenate words with underscore

ISTM6200 / Summer 2021
Keywords
• Reserved words (keywords) in Python 3
They must be spelled exactly as written here!

ISTM6200 / Summer 2021
Exercise: Naming and Using Variables
1) Store a message in a variable, and then print the message
2) Store a message in a variable and print the message. Then
change the value of your variable to a new message, and
print the new message

ISTM6200 / Summer 2021
Data Types
• Python has five standard data types: numbers,
strings, lists, tuples, and dictionaries.
• In Python, we do not need to explicitly define or
declare the type of a variable.
• x = 3 implies x is of ?? type
• y = “OK” implies y is of ?? type
• How to find the type of a variable? type(…)
• type(x)
• type(y)

ISTM6200 / Summer 2021
Basic Data Types in Python
• Numbers
• Integers: x = 2, y = 5
• Floats: x = 3.456, y = 9823.9
• Strings
• my_name = “Yixin”
• my_course = ‘Introduction to Programming’
• Lists: e.g., my_lst = [1,2,3, ‘number’]
• Tuples: e.g., my_tpl = (1,2,3, ‘abc’)
• Dictionaries: e.g., my_dict = {‘name’: ‘Amy’, ‘age’: 18}