Python类概念理解与创建方法咨询，附示例代码求解析

Hey there! Let's break down Python classes using your example code—this will make everything click, I promise. Classes can feel confusing at first, but once you see how they tie data and actions together, it'll make total sense.

Think of a class as a blueprint or mold. It defines what properties (data) and actions (functions, called "methods") every object made from it will have. For example, a Prob class is a blueprint for objects that handle problem files—each Prob object will know how to read a file, build a problem from it, and store the related data.

Here's your code again, with explanations for each part:

class Prob(object): 
    def __init__ (self,filename): 
        self.file_contents = read_file(filename) 
    def prob_build(self): 
        self.problem, self.aux_vars = build_problem(file_contents) 

first_object = Prob(some_file) 

1. Defining the Class: class Prob(object): #

• class is the keyword that tells Python "we're making a blueprint here".
• Prob is the name of our blueprint—by convention, class names start with a capital letter to distinguish them from regular variables/functions.
• (object) means our Prob class inherits from Python's basic object class (this is optional in Python 3, but writing it makes it clear we're building a standard object).

2. The Initializer: __init__ Method #

This is the constructor—it runs automatically when you create a new object from the class, and it sets up the object's initial properties.

• self: This is the most important part! It refers to the specific object being created (think of it as "this object"). Every method in a class needs self as its first parameter so it can access the object's data.
• filename: This is a parameter you pass when creating the object (like some_file in your code).
• self.file_contents = read_file(filename): This creates a property called file_contents for the object, and sets its value to the result of reading the file. Later, you can access this data with first_object.file_contents.

3. A Custom Method: prob_build #

This is an action the object can perform—in your case, building a problem from the file contents.

• Again, self is the first parameter, so the method can access the object's properties.
• Quick fix: Your code has a small bug here—build_problem(file_contents) should be build_problem(self.file_contents). Because file_contents is stored as a property of the object, you need to use self. to access it (otherwise Python won't know where to find file_contents).
• After fixing it, when you call first_object.prob_build(), the method will create two new properties: first_object.problem and first_object.aux_vars, which hold the results of build_problem.

4. Creating an Object (Instance): first_object = Prob(some_file) #

This is where we use the blueprint to make a real, usable object. When you run this line:

1. Python creates a new Prob object.
2. It automatically calls the __init__ method, passing some_file as the filename parameter.
3. The object is initialized with its file_contents property, ready to use.

Classes let you bundle data and the actions that work on that data together, which makes your code cleaner and more organized. For example:

• You can create multiple Prob objects for different files, each with their own independent file_contents, problem, and aux_vars properties.
• If you need to add more functionality later (like saving the problem to a file), you just add a new method to the Prob class, and all existing Prob objects can use it.

• Don't forget self as the first parameter for class methods—without it, the method can't access the object's properties.
• When accessing object properties inside methods, always use self. (like self.file_contents, not just file_contents).
• self isn't a keyword—you could name it this if you wanted, but everyone uses self in Python, so stick with that to keep your code readable.

内容的提问来源于stack exchange，提问作者bluetooth