Learning Python Design Patterns – Second Edition - PDF Free Download
Mastering Object-Oriented Python, 2nd Edition. Add favorites. Complete with practical examples, the book guides you through the advanced concepts of OOP in Python, and demonstrates how you can apply them to solve complex problems in OOP. You will learn how to create high-quality Python programs by exploring design alternatives and determining which design offers the best performance. Develop an understanding of Creational Design Patterns and the different object creation methods that help you solve issues in software development.
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Use Structural Design Patterns and find out how objects and classes interact to build larger applications. With the increasing focus on optimized software architecture and design it is important that software architects think about optimizations in object creation, code structure, and interaction between objects at the architecture or design level.
This makes sure that the cost of software maintenance is low and code can be easily reused or is adaptable to change.
The key to this is reusability and low maintenance in design patterns. We start by introducing design patterns from the Python perspective. It also covers observer patterns, command patterns, and compound patterns. By the end of the book, you will have enhanced your professional abilities in software architecture, design, and development.
In derivative classes, the former contains code that will undo that command, and the latter returns a boolean value that defines if the command is undoable. Reversible allows some commands to be non-undoable, such as a Save command. All executed Commands are kept in a list with a method of keeping a "present" marker directly after the most recently executed command. A request to undo will call the Command. Unexecute directly before "present", then move "present" back one command. Conversely, a Redo request will call Command.
Execute after "present", and move "present" forward one. This Command approach is an implementation of the Command pattern. It encapsulates requests in objects, and uses a common interface to access those requests. Thus, the client can handle different requests, and commands can be scattered throughout the application. This is the document editor's ability to textually analyze the contents of a document.
Although there are many analyses that can be performed, spell check and hyphenation-formatting are the focus. Removing the integer-based index from the basic element allows for a different iteration interface to be implemented. This will require extra methods for traversal and object retrieval. These methods are put into an abstract Iterator interface.
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Each element then implements a derivation of the Iterator , depending on how that element keeps its list ArrayIterator , LinkListIterator , etc. Functions for traversal and retrieval are put into the abstract Iterator interface. Future Iterators can be derived based on the type of list they will be iterating through, such as Arrays or Linked Lists. Thus, no matter what type of indexing method any implementation of the element uses, it will have the appropriate Iterator.
This is an implementation of the Iterator pattern. It allows the client to traverse through any object collection, without needing to access the contents of the collection directly, or be concerned about the type of list the collection's structure uses. Now that traversal has been handled, it is possible to analyze the elements of a structure. It is not feasible to build each type of analysis into the element structure themselves; every element would need to be coded, and much of the code would be the same for similar elements.
Instead, a generic CheckMe method is built into the element's abstract class. Each Iterator is given a reference to a specific algorithm such as spell check, grammar check, etc. When that Iterator iterates through its collection, it calls each element's CheckMe , passing the specified algorithm. CheckMe then passes a reference to its element back to said algorithm for analysis. Thus, to perform a spell check, a front-to-end iterator would be given a reference to a SpellCheck object.
The iterator would then access each element, executing its CheckMe method with the SpellCheck parameter. Each CheckMe would then call the SpellCheck , passing a reference to the appropriate element. In this manner, any algorithm can be used with any traversal method, without hard-code coupling one with the other. For example, Find can be used as "find next" or "find previous", depending on if a "forward" iterator was used, or a "backwards" iterator.
In addition, the algorithms themselves can be responsible for dealing with different elements. For example, a SpellCheck algorithm would ignore a Graphic element, rather than having to program every Graphic -derived element to not send themselves to a SpellCheck. Creational patterns are ones that create objects, rather than having to instantiate objects directly.
This gives the program more flexibility in deciding which objects need to be created for a given case. These concern class and object composition. They use inheritance to compose interfaces and define ways to compose objects to obtain new functionality.
Most of these design patterns are specifically concerned with communication between objects. Criticism has been directed at the concept of software design patterns generally, and at Design Patterns specifically.
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Paul Graham wrote: . When I see patterns in my programs, I consider it a sign of trouble. The shape of a program should reflect only the problem it needs to solve. Any other regularity in the code is a sign, to me at least, that I'm using abstractions that aren't powerful enough-- often that I'm generating by hand the expansions of some macro that I need to write.
In an interview with InformIT in , Erich Gamma stated that the book authors had a discussion in on how they would have refactored the book and concluded that they would have recategorized some patterns, added a few additional ones and removed one of them Singleton altogether. From Wikipedia, the free encyclopedia. Not to be confused with the concept of a design pattern. This article has multiple issues. Please help improve it or discuss these issues on the talk page.
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