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This module explains the Python loop modifiers: else, continue, break,and pass.

Table of contents

Preface

This module is one in a collection of modules on Python designed for teaching ITSE 1359 Introduction to Scripting Languages: Python at Austin Community College in Austin, TX.

What you have learned

You have learned how to construct while loops, for loops, and if statements in recent modules on control flow in Python. In addition, you recently learned how to create nested loop structures .

What you will learn

In this module, you will learn how to add an else clause to while loops and for loops. In addition, once you start using nested loops, you need to know how to use the loop modifiers: continue and break . Those loop modifiers will be explained in this module.

Finally, this module will make a brief mention of the pass statement, which does nothing. If you need to write code that does nothing, the pass statement is for you.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the Figuresand the Listings while you are reading about them.

(Note to blind and visually impaired students: most of the Figures and all of the Listings inthis module are presented in plain text format and should be accessible using an audio screen reader or a braille display. Note however that the requiredindentation may not be properly represented by an audio screen reader.)

Figures

  • Figure 1 . Output from the code in Listing 1.
  • Figure 2 . Output from the code in Listing 2.
  • Figure 3 . Output from the code in Listing 3.

Listings

  • Listing 1 . Loops with else clauses.
  • Listing 2 . Nested loops with a continue statement.
  • Listing 3 . Nested loops with a break statement.

Discussion and sample code

The else clause

You learned about the else clause on an if statement in an earlier module titled Itse1359-1230-The if Statement .

Loop statements can also have an else clause. The else clause on a for loop is executed when the loop terminates through exhaustion of the elements in the list.The else clause on a while loop is executed when the loop terminates because the condition becomes False . The else clause is not executed when the loop is terminated by a break statement.

I will illustrate the else clause using a program that is similar to the odometer program that you learned about in the earlier module titled Itse1359-1250-Nested Loops . The program is shown in Listing 1 .

Listing 1 . Loops with else clauses.
# Illustrates nested loops with else clauses #---------------------------------------------------------------------------leftDigit = 0 rightDigit = 0#Begin outer while loop while leftDigit<2: leftDigit += 1#Begin for loop for middleDigit in range(1,3):rightDigit = 0 #Begin innermost while loopwhile rightDigit<3: rightDigit += 1print(str(leftDigit) + "-" + str(middleDigit) + "-" + str(rightDigit)) else:print("In else clause on inner while loop") #end inner while loop with else clauseelse: print("In else clause on for loop")#end for loop with else clause else:print("In else clause on outer while loop") #end outer while loop with else clauseprint("Goodbye")

Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Itse 1359 introduction to scripting languages: python. OpenStax CNX. Jan 22, 2016 Download for free at https://legacy.cnx.org/content/col11713/1.32
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