10. The Iterator Pattern
by Sebastian Raschka, Robert Layton, Martin Czygan, Phuong Vo.T.H, Fabrizio Romano,
Python: Real-World Data Science
- Data Science with Python
- Table of Contents
- Data Science with Python
- Meet Your Course Guide
- What's so cool about Data Science?
- Course Structure
- Course Journey
- The Course Roadmap and Timeline
- 1. Course Module 1: Python Fundamentals
- 1. Introduction and First Steps – Take a Deep Breath
- A proper introduction
- Enter the Python
- About Python
- What are the drawbacks?
- Who is using Python today?
- Setting up the environment
- What you need for this course
- How you can run a Python program
- How is Python code organized
- Python's execution model
- Guidelines on how to write good code
- The Python culture
- A note on the IDEs
- 2. Object-oriented Design
- 3. Objects in Python
- 4. When Objects Are Alike
- 5. Expecting the Unexpected
- 6. When to Use Object-oriented Programming
- 7. Python Data Structures
- 8. Python Object-oriented Shortcuts
- 9. Strings and Serialization
- 10. The Iterator Pattern
- 11. Python Design Patterns I
- 12. Python Design Patterns II
- 13. Testing Object-oriented Programs
- 14. Concurrency
- 1. Introduction and First Steps – Take a Deep Breath
- 2. Course Module 2: Data Analysis
- 1. Introducing Data Analysis and Libraries
- 2. NumPy Arrays and Vectorized Computation
- 3. Data Analysis with pandas
- 4. Data Visualization
- 5. Time Series
- 6. Interacting with Databases
- 7. Data Analysis Application Examples
- 3. Course Module 3: Data Mining
- 1. Getting Started with Data Mining
- 2. Classifying with scikit-learn Estimators
- 3. Predicting Sports Winners with Decision Trees
- 4. Recommending Movies Using Affinity Analysis
- 5. Extracting Features with Transformers
- 6. Social Media Insight Using Naive Bayes
- 7. Discovering Accounts to Follow Using Graph Mining
- 8. Beating CAPTCHAs with Neural Networks
- 9. Authorship Attribution
- 10. Clustering News Articles
- 11. Classifying Objects in Images Using Deep Learning
- 12. Working with Big Data
- 13. Next Steps…
- Chapter 1 – Getting Started with Data Mining
- Chapter 2 – Classifying with scikit-learn Estimators
- Chapter 3: Predicting Sports Winners with Decision Trees
- Chapter 4 – Recommending Movies Using Affinity Analysis
- Chapter 5 – Extracting Features with Transformers
- Chapter 6 – Social Media Insight Using Naive Bayes
- Chapter 7 – Discovering Accounts to Follow Using Graph Mining
- Chapter 8 – Beating CAPTCHAs with Neural Networks
- Chapter 9 – Authorship Attribution
- Chapter 10 – Clustering News Articles
- Chapter 11 – Classifying Objects in Images Using Deep Learning
- Chapter 12 – Working with Big Data
- More resources
- 4. Course Module 4: Machine Learning
- 1. Giving Computers the Ability to Learn from Data
- How to transform data into knowledge
- The three different types of machine learning
- An introduction to the basic terminology and notations
- A roadmap for building machine learning systems
- Using Python for machine learning
- 2. Training Machine Learning Algorithms for Classification
- 3. A Tour of Machine Learning Classifiers Using scikit-learn
- 4. Building Good Training Sets – Data Preprocessing
- 5. Compressing Data via Dimensionality Reduction
- 6. Learning Best Practices for Model Evaluation and Hyperparameter Tuning
- 7. Combining Different Models for Ensemble Learning
- 8. Predicting Continuous Target Variables with Regression Analysis
- Introducing a simple linear regression model
- Exploring the Housing Dataset
- Implementing an ordinary least squares linear regression model
- Fitting a robust regression model using RANSAC
- Evaluating the performance of linear regression models
- Using regularized methods for regression
- Turning a linear regression model into a curve – polynomial regression
- A. Reflect and Test Yourself! Answers
- Module 2: Data Analysis
- Module 3: Data Mining
- Chapter 1: Getting Started with Data Mining
- Chapter 2: Classifying with scikit-learn Estimators
- Chapter 3: Predicting Sports Winners with Decision Trees
- Chapter 4: Recommending Movies Using Affinity Analysis
- Chapter 5: Extracting Features with Transformers
- Chapter 6: Social Media Insight Using Naive Bayes
- Chapter 7: Discovering Accounts to Follow Using Graph Mining
- Chapter 8: Beating CAPTCHAs with Neural Networks
- Chapter 9: Authorship Attribution
- Chapter 10: Clustering News Articles
- Chapter 11: Classifying Objects in Images Using Deep Learning
- Chapter 12: Working with Big Data
- Module 4: Machine Learning
- Chapter 1: Giving Computers the Ability to Learn from Data
- Chapter 2: Training Machine Learning
- Chapter 3: A Tour of Machine Learning Classifiers Using scikit-learn
- Chapter 4: Building Good Training Sets – Data Preprocessing
- Chapter 5: Compressing Data via Dimensionality Reduction
- Chapter 6: Learning Best Practices for Model Evaluation and Hyperparameter Tuning
- Chapter 7: Combining Different Models for Ensemble Learning
- Chapter 8: Predicting Continuous Target Variables with Regression Analysis
- B. Bibliography
- 1. Giving Computers the Ability to Learn from Data
- Index
We've discussed how many of Python's built-ins and idioms that seem, at first blush, to be non-object-oriented are actually providing access to major objects under the hood. In this chapter, we'll discuss how the for loop that seems so structured is actually a lightweight wrapper around a set of object-oriented principles. We'll also see a variety of extensions to this syntax that automatically create even more types of object. We will cover:
- What design patterns are
- The iterator protocol—one of the most powerful design patterns
- List, set, and dictionary comprehensions
- Generators and coroutines
When engineers and architects decide to build a bridge, or a tower, or a building, they follow certain principles to ensure structural integrity. There are various possible designs for bridges (suspension or cantilever, for example), but if the engineer doesn't use one of the standard designs, and doesn't have a brilliant new design, it is likely the bridge he/she designs will collapse.
Design patterns are an attempt to bring this same formal definition for correctly designed structures to software engineering. There are many different design patterns to solve different general problems. People who create design patterns first identify a common problem faced by developers in a wide variety of situations. They then suggest what might be considered the ideal solution for that problem, in terms of object-oriented design.
Knowing a design pattern and choosing to use it in our software does not, however, guarantee that we are creating a "correct" solution. In 1907, the Québec Bridge (to this day, the longest cantilever bridge in the world) collapsed before construction was completed, because the engineers who designed it grossly underestimated the weight of the steel used to construct it. Similarly, in software development, we may incorrectly choose or apply a design pattern, and create software that "collapses" under normal operating situations or when stressed beyond its original design limits.
Any one design pattern proposes a set of objects interacting in a specific way to solve a general problem. The job of the programmer is to recognize when they are facing a specific version of that problem, and to adapt the general design in their solution.
In this chapter, we'll be covering the iterator design pattern. This pattern is so powerful and pervasive that the Python developers have provided multiple syntaxes to access the object-oriented principles underlying the pattern. We will be covering other design patterns in the next two chapters. Some of them have language support and some don't, but none of them is as intrinsically a part of the Python coder's daily life as the iterator pattern.
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