Gaddis Python 3e Chapter 02 PPT (1).ppt

Copyright © 2015 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
C H A P T E R 2
Input,
Processing,
and Output

Topics
Displaying Output with print Function
Comments
Variables
Reading Input from the Keyboard
Performing Calculations
More About Data Output

Displaying Output with the
print Function
Function: piece of prewritten code that
performs an operation
print function: displays output on the
screen
Argument: data given to a function
Example: data that is printed to screen
Statements in a program execute in the
order that they appear
From top to bottom

Strings and String Literals
String: sequence of characters that is
used as data
String literal: string that appears in
actual code of a program
Must be enclosed in single (‘) or double (“)
quote marks
String literal can be enclosed in triple quotes
(''' or """)
Enclosed string can contain both single and double
quotes and can have multiple lines

Comments
Comments: notes of explanation within
a program
Ignored by Python interpreter
Intended for a person reading the program’s code
Begin with a # character
End-line comment: appears at the end
of a line of code
Typically explains the purpose of that line

Variables
Variable: name that represents a value
stored in the computer memory
Used to access and manipulate data stored in
memory
A variable references the value it represents
Assignment statement: used to create a
variable and make it reference data
General format is variable = expression
Example: age = 29
Assignment operator: the equal sign (=)

Variable Naming Rules
Rules for naming variables in Python:
Variable name cannot be a Python key word
Variable name cannot contain spaces
First character must be a letter or an
underscore
After first character may use letters, digits, or
underscores
Variable names are case sensitive
Variable name should reflect its use

Displaying Multiple Items with
the print Function
Python allows one to display multiple
items with a single call to print
Items are separated by commas when passed
as arguments
Arguments displayed in the order they are
passed to the function
Items are automatically separated by a space
when displayed on screen

Variable Reassignment
Variables can reference different values
while program is running
Garbage collection: removal of values
that are no longer referenced by
variables
Carried out by Python interpreter
A variable can refer to item of any type
Variable that has been assigned to one type
can be reassigned to another type

Numeric Data Types, Literals,
and the str Data Type
Data types: categorize value in memory
e.g., int for integer, float for real number, str
used for storing strings in memory

Reassigning a Variable to a
Different Type
A variable in Python can refer to items of
any type

Reading Input from the
Keyboard
Most programs need to read input from
the user
Built-in input function reads input
from keyboard
Returns the data as a string
Format: variable = input(prompt)
prompt is typically a string instructing user to
enter a value
Does not automatically display a space after
the prompt

Performing Calculations
Math expression: performs calculation
and gives a value
Math operator: tool for performing calculation
Operands: values surrounding operator
Variables can be used as operands
Resulting value typically assigned to variable
Two types of division:
/ operator performs floating point division
// operator performs integer division
Positive results truncated, negative rounded away
from zero

Operator Precedence and
Grouping with Parentheses
Python operator precedence:
1. Operations enclosed in parentheses
Forces operations to be performed before others
2. Exponentiation (**)
3. Multiplication (*), division (/ and //), and
remainder (%)
4. Addition (+) and subtraction (-)
Higher precedence performed first
Same precedence operators execute from left
to right

The Exponent Operator and
the Remainder Operator
Exponent operator (**): Raises a
number to a power
x ** y = xy
Remainder operator (%): Performs
division and returns the remainder
a.k.a. modulus operator
e.g., 4%2=0, 5%2=1
Typically used to convert times and distances,
and to detect odd or even numbers

Breaking Long Statements
into Multiple Lines
Long statements cannot be viewed on
screen without scrolling and cannot be
printed without cutting off
Multiline continuation character ():
Allows to break a statement into
multiple lines
Example:
print(‘my first name is’,
first_name)

More About Data Output
(cont’d.)
Special characters appearing in string
literal
Preceded by backslash ()
Examples: newline (n), horizontal tab (t)
Treated as commands embedded in string
When + operator used on two strings in
performs string concatenation
Useful for breaking up a long string literal

Formatting Numbers
Can format display of numbers on
screen using built-in format function
Two arguments:
Numeric value to be formatted
Format specifier
Returns string containing formatted number.

Formatting Numbers (cont’d.)
The % symbol can be used in the format
string of format function to format
number as percentage
To format an integer using format
function:
Use d as the type designator
Do not specify precision
Can still use format function to set field
width or comma separator

Summary
This chapter covered:
The program de velopment cycle, tools for
program design, and the design process
Ways in which programs can receive input,
particularly from the keyboard
Ways in which programs can present and
format output
Use of comments in programs
Uses of variables
Tools for performing calculations in programs

Gaddis Python 3e Chapter 02 PPT (1).ppt

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