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This module explains Python decision logic in general and the if statement in particular.

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 were introduced to decision logic in the earlier module titled Itse 1359-1210-The While Loop . In that module I told you that Python supports a stand-alone decision capability, the if statement, which would be discussed in a future module. This is that future module.

You learned about the relational and logical operators that are used in decision logic in the module titled Itse1359-1220-Operators .

What you will learn

In this module, you will learn about

  • the if statement
  • the if...else statement
  • nested if statements

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 . Pseudo-code for an if statement.
  • Figure 2 . Output from the code in Listing 1.
  • Figure 3 . Visualization of the code in Listing 1.
  • Figure 4 . Pseudo-code for a Python if...else statement.
  • Figure 5 . Output from the code in Listing 2.
  • Figure 6 . Output from the code in Listing 3.

Listings

  • Listing 1 . Example of if statement usage.
  • Listing 2 . Example of if...else statement usage.
  • Listing 3 . Example of nested if statements.

Discussion and sample code

The if statement

The pseudo-code for a Python if statement is shown in Figure 1 .

Figure 1 . Pseudo-code for an if statement.
if expression is True: Execute one or more statements at same indentation levelExecute next statement

The expression must be one that will evaluate to either True or False.

If the expression evaluates to True, the indented statement(s) that follow the colon will be executed in sequence.

If the expression evaluates to False, those indented statements will be skipped and the next statement following the if statement will be executed.

Listing 1 shows an example of the use of an if statement.

Listing 1 . Example of if statement usage.
# Illustrates the if statement ##------------------------------- dogs = ["Affenpinscher","Afgan Hound","Akita"]if len(dogs)>2: print(dogs[0]) print(dogs[1]) print(dogs[2]) print("Length of dogs list = " + str(len(dogs)))if len(dogs) == 2: print(dogs[0]) print(dogs[1]) print(dogs[2])print(dogs)

Questions & Answers

Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
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what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
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Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
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Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
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not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
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I'm interested in Nanotube
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this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
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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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