This document introduces the basics of Python programming. It discusses motivations for learning Python such as writing programs to calculate loan payments. It then lists objectives for learning variables, operators, expressions, input/output functions, and the software development process. An example program is provided to calculate the area of a circle to demonstrate how a program works step-by-step from assigning values to variables to displaying results. Input from the user is discussed as well as using eval() to evaluate strings as expressions.

1. 1.2 Basics of Python
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2. Motivations
Suppose, for example, that you need to take out a
student loan. Given the loan amount, loan term,
and annual interest rate, can you write a program
to compute the monthly payment and total
payment? This chapter shows you how to write
programs like this. Along the way, you learn the
basic steps that go into analyzing a problem,
designing a solution, and implementing the
solution by creating a program.
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3. Objectives
• To write programs that perform simple computations (§2.2).
• To obtain input from a program’s user by using the input function
(§2.3).
• To use identifiers to name variables (§2.4).
• To assign data to variables (§2.5).
• To define named constants (§2.6).
• To use the operators +, -, *, /, //, %, and ** (§2.7).
• To write and evaluate numeric expressions (§2.8).
• To use augmented assignment operators to simplify coding (§2.9).
• To perform numeric type conversion and rounding with the int and
round functions (§2.10).
• To obtain the current system time by using time.time() (§2.11).
• To describe the software development process and apply it to
develop the loan payment program (§2.12).
• To compute and display the distance between two points (§2.13).
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4. Introducing Programming with an
Example
Listing 2.1 Computing the Area of a
Circle
This program computes the area of
the circle.
4
ComputeArea
Run
IMPORTANT NOTE:
(1) To enable the buttons, you must download the entire slide
file slide.zip and unzip the files into a directory (e.g.,
c:slide). (2) You must have installed Python and set python
bin directory in the environment path. (3) If you are using
Office 2010, check PowerPoint2010.doc located in the
same folder with this ppt file.
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5. Trace a Program Execution
# Assign a radius
radius = 20 # radius is now 20
# Compute area
area = radius * radius * 3.14159
# Display results
print("The area for the circle of radius " +
str(radius) + " is " + str(area))
5
20radius
Assign 20 to
radius
animation
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6. Trace a Program Execution
# Assign a radius
radius = 20 # radius is now 20
# Compute area
area = radius * radius * 3.14159
# Display results
print("The area for the circle of radius“,
radius, " is "area)
6
20radius
Assign result to
area
animation
1256.636area
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7. Trace a Program Execution
# Assign a radius
radius = 20 # radius is now 20
# Compute area
area = radius * radius * 3.14159
# Display results
print("The area for the circle of radius",
radius, "is", area)
7
20radius
print a message to
the console
animation
1256.636area
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8. Reading Input from the Console
8
1. Use the input function
variable = input("Enter a string: ")
2. Use the eval function
var = eval(stringVariable)
eval("51 + (54 * (3 + 2))") returns 321.
ComputeAreaWithConsoleInput
Run
ComputeAverage
Run
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