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Chapter 5 Repetition Structures. STARTING OUT WITH Python First Edition by Tony Gaddis. 5.1 Introduction to Repetition Structures. Concept: The repetition structure causes a statement or set of statements to execute repeatedly. 5.1 Introduction to Repetition Structures.

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Starting out with python first edition by tony gaddis

Chapter 5Repetition Structures

STARTING OUT WITH

PythonFirst Edition

by Tony Gaddis


5 1 introduction to repetition structures

5.1 Introduction to Repetition Structures

Concept:

The repetition structure causes a statement or set of statements to execute repeatedly.


5 1 introduction to repetition structures1

5.1 Introduction to Repetition Structures

  • Condition-Controlled and Count-Controlled Loops

  • A condition-controlled loop uses a true/false condition to control the number of times that it repeats.

  • A count-controlled loop repeats a specific number of times.


5 2 the while loop a condition controlled loop

5.2 The while Loop: a Condition-Controlled Loop

Concept:

A condition-controlled loop causes a statement or set of statements to repeat as long as a condition is true. In Python you use the while statement to write a condition-controlled loop.


5 2 the while loop a condition controlled loop1

5.2 The while Loop: a Condition-Controlled Loop

  • In Python …

  • while condition:

  • statement

  • statement

  • etc.

Figure 5-1 The logic of a while loop


5 2 the while loop a condition controlled loop2

5.2 The while Loop: a Condition-Controlled Loop

Figure 5-2 The while loop


5 2 the while loop a condition controlled loop3

5.2 The while Loop: a Condition-Controlled Loop

  • The while Loop is a Pretest Loop, which means it tests its condition before performing an iteration.


5 3 the for loop a count controlled loop

5.3 The for Loop: a Count-Controlled Loop

Concept:

A count-controlled loop iterates a specific number of times. In Python you use the for statement to write a count-controlled loop.


5 3 the for loop a count controlled loop1

5.3 The for Loop: a Count-Controlled Loop

  • In Python …

  • for variable in [value1, value2, etc.]:

  • statement

  • statement

  • etc.


5 3 the for loop a count controlled loop2

5.3 The for Loop: a Count-Controlled Loop

  • Using the range Function with the for Loop

  • for num in [0, 1, 2, 3, 4]:

  • print num

  • for num in range(5):

  • print num


5 3 the for loop a count controlled loop3

5.3 The for Loop: a Count-Controlled Loop

  • Using the range Function with the for Loop

  • for num in range(1, 10, 2):

  • print num

  • First argument, 1, is the starting value for the list

  • Second argument, 10, is the ending limit of the list

  • Third argument, 2, is the step value


5 3 the for loop a count controlled loop4

5.3 The for Loop: a Count-Controlled Loop

Program 5-12 (user_squares2.py)


5 3 the for loop a count controlled loop5

5.3 The for Loop: a Count-Controlled Loop

  • Generating Lists that Range from

  • Highest to Lowest

  • for num in range(5, 0, -1):

  • print num


5 4 calculating a running total

5.4 Calculating a Running Total

Concept:

A running total is a sum of numbers that accumulates with each iteration of a loop. The variable used to keep the running total is called an accumulator.


5 4 calculating a running total1

5.4 Calculating a Running Total

  • Programs that calculate the total of a series of numbers typically use two elements:

  • A loop that reads each number in the series

  • A variable that accumulates the total of the numbers as they are read.


5 4 calculating a running total2

5.4 Calculating a Running Total

Figure 5-7 Logic for calculating a running total


5 4 calculating a running total3

5.4 Calculating a Running Total

  • The Augmented Assignment Operators

Table 5-2 The age variable references the value 25


5 5 sentinels

5.5 Sentinels

Concept:

A sentinel is a special value that marks the end of a sequence of values.


5 6 input validation loops

5.6 Input Validation Loops

Concept:

Input validation is the process of inspecting data that has been input to a program, to make sure it is valid before it is used in a computation. Input validation is commonly done with a loop that iterates as long as an input variable references bad data.


5 6 input validation loops1

5.6 Input Validation Loops

  • Error Trap or Error Handler

Figure 5-8 Logic containing an input validation loop


5 6 input validation loops2

5.6 Input Validation Loops

  • Priming Read

  • # Get a test score.

  • Score = input(‘Enter a test score: ‘)

  • # Make sure it is not less than 0.

  • while score < 0:

  • print ‘ERROR: The score cannot be negative.’

  • score = input (‘Enter the correct score: ‘)


5 7 nested loops

5.7 Nested Loops

Concept:

A loop that is inside another loop is called a nested loop.


5 7 nested loops1

5.7 Nested Loops

  • for hours in range(24):

  • for minutes in range(60):

  • for seconds in range(60):

  • print hours, ‘:’, minutes, ‘:’, seconds

  • About Nested Loops:

  • The inner loop goes through all of its iterations for every single iteration of the outer loop

  • Inner loops complete their iterations faster than outer loops


Starting out with python first edition by tony gaddis

Chapter 5Repetition Structures

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