Home > Articles > Open Source > Python

An Introduction to Object-Oriented Concepts in Python, Part 5

  • Print
  • + Share This
Programming expert Jesse Smith shows how to improve Python program design by using data structures.
Like this article? We recommend

In this article, I'll continue showing you how to use Python from an object-oriented (OO) point of view. If you're unfamiliar with object-oriented concepts such as inheritance, encapsulation, and polymorphism, read my article "A Primer on Object-Oriented Concepts" before continuing with this article.

This article builds on my earlier article "An Introduction to Object-Oriented Concepts in Python, Part 4." If you haven't read that article already, please read it before reading this article. The concepts in this article will take a closer look at using data structures such as tuples, dictionairies, and lists.

If you've been following my Python series, you know how object-oriented concepts such as subclassing using object inheritance in Python work. But so far I haven't addressed how data structures can be used to improve your code flow and class design. As in other programming languages, it's necessary to have data structures that allow us to store and retrieve information, eliminate spiked code patterns, and improve our overall application design by making a smaller footprint thru less redundancy.


Catch Up on All of the Articles in this Python Series

Jesse Smith has written five articles in this series. Here are the earlier installments:

Part 1
Part 3
Part 2
Part 4


Tuples

Python has a lot of built-in objects, many of which include support for data structures. In Python, these objects are referred to as native data types. One such native data-type is a Tuple. A Tuple is like a list object, but is immutable. The elements of a Tuple are stored in parentheses, instead of brackets as they are with a list:

x = ("a","b","c","d")

Tuples are ideal for combining different data types. For example, if storing information about a book, we would store the author's name, price of the book, number of books in stock, and so on. This data would be in String and Integer types. But we're not restricted to primitive data types, and we can store our own types as well. One of the biggest advantages of Tuples is that we can use them as values inside other storage objects like the List object.

Let's get to the fun stuff about using Tuples. We can use a Tuple in place of a bunch of if conditions as a for loop. Let's say we have paired values that represent a stock name and a price. Without a Tuple, multiple if conditions can be used to determine what stock to pick and the price to associate with it:

if stock == "Google":
    price = 800
elif stock == "APPL":
    price = 400

This could be quite a long list of all major stock symbols. We can shorten our code quite a bit by using a Tuple:

stockVals = [("GOOG",800),("APPL",400)]
for(name,price) in stockVals:
                   [...]

In this example, we associate the price to a symbol, and the logic to handle each stock can be placed inside the for loop, instead of having multiple if conditions. This example demonstrates using Tuples inside lists. Thus far, the Tuple examples are of unnamed Tuples. As you can probably guess, you can apply a name to a Tuple. Take the following simple example:

from collections import namedtuple
Point = namedtuple('Point', 'x y')
pt1 = Point(2.0, 5.0)
pt2 = Point(3.5, 1.5)

In order to name a Tuple, we have to import the namedtuple base class. From there, we can pass in the name and values of our Tuple to the namedtuple class, which returns an object that can be assigned to a variable. This essentially allows a Tuple to become a class object type.

Tuples have no methods for adding, removing, or searching the elements. Tuples can also be used as keys in dictionaries. They're faster and safer than lists, but can be converted to a list if necessary.

Dictionaries

A dictionary in Python is similar to a Hashmap in other languages. To define a dictionary, we assign key-to-value relationships:

stocks = {"GOOG":"800","APPL":"400"}

In this example, "GOOG" represents a key, while the stock price represents the value. You can retrieve values by keys, but you cannot retrieve keys by values. We can use the get method to retrieve a value:

print(stocks.get("GOOG"))

Remember, Tuples can be used as values in a dictionary:

stocks = {"GOOG":(800,850,900,950)}

Any problems accessing the dictionary will result as a KeyError exception.

To iterate a dictionary, you can use the handy items method:

for stock,values in stocks.items():
    print(stock, values[0])

Each key and value are unpacked into the stock and values variables we define. The values variable is a Tuple, and the 0 index accesses the first value of the Tuple.

Lists

The most common native data type is none other than the list storage data type. Unlike the previous storage data types we've considered, the list is an order data type. Lists should be used when there are numerous objects with the same type that need an action performed on them. Lists should not be used for storing attributes of particular objects, such as items for which Tuples and dictionaries are often used.

Storing different data types in a list makes them more difficult to access in a loop structure than the other storage types discussed so far. The list has some fancy method for ordering elements, however, such as the reverse and sort methods. The reverse method does what you would expect, which is to reverse all the elements in the list or turn them around. This is another reason to use the same data types in lists—because they can be ordered (that is, strings or integers).

To sort a list in place, without creating a new list, use the sort method:

stocks = ["GOOG","APPL","SPWR","SCTY"]
stocks.sort()
print(stocks)

To create a new sorted list, use the sorted method:

a = sorted([3,2,3,1,5])
print(a)

To sort a list of Tuples, do the following:

stocks = [("GOOG",800),("APPL",400),("SPWR",27),("SCTY",42)]
stocks.sort(key=lambda i: i[1])
print(stocks)

The lambda keyword creates a function that takes the Tuple as an argument and returns an indexed list. In this example, the list of Tuples is sorted by price in ascending order.

Conclusion

In this article, you learned more about using data structures in an object-oriented context. One such data structure, the Tuple, is useful for combining different data types. The Tuple's biggest advantage is being able to use it as keys in a dictionary, or as elements in a ;ist. You can also create named Tuples, thus making them an object type reference similar to a class.

Dictionaries are high-performance lists that use a key as an index to reference a corresponding value. They're similar to HashMaps in Java. The dictionary object in Python has some easy-to-use powerful methods, like the items method for traversing the values.

The list object is the most common "jack of all trades" storage data type. The list object is an ordered storage container that's useful when you need to store similar data types. The list object  can traverse Tuples as the elements by using the lambda function.

At this stage, you should be comfortable using the built-in storage data types and using them for better class design and code flow. Keep experimenting with each type of storage object and extending them as needed in your programs.

This concludes the OO Python series. I hope you enjoyed it and learned much from these articles. In the future, I plan to continue my overall Python coverage by introducing the Python Pyramid framework for web applications.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020