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    <p>Example 1: "better (shorter, encapsulated, more error-proof)"</p> <p>Not really. </p> <ul> <li><p>The example 1 function call is no shorter than example 2; you have to set the instance variables before calling the function instead of passing the values as arguments. It's the same code.</p></li> <li><p>The example 1 function call is no more encapsulated. Encapsulation is a property of the class <em>as a whole</em>, not an individual method. Methods are just methods, and they often have arguments so that they're clear, obvious, replaceable and easy to test.</p></li> <li><p>The example 1 function call is not error-proof in any sense of the word. You're just as likely to forget to set the instance variable as you are to forget to pass the instance variable in the function call. </p> <p>When you have explicit arguments (example 2), Python can check to see that you provided the correct number of arguments. In example 1, there's no checking done for you.</p></li> </ul> <p>Example 1: "harder to test"</p> <p>Agreed.</p> <p><strong>Summary</strong></p> <p>Instance variables are special. They reflect the state of being of some object. For model objects, they're serious business because they're often persistent. For GUI objects, they're "what's being displayed right now" which is often transient.</p> <p>Don't over-use instance variables. Instance variables should be meaningful and significant. Not just junk variables for things that don't have a proper home anywhere else.</p> <p>Method functions are just functions. In an OO world, they're still just functions. They map input arguments to output results (or object state changes). Pass all the arguments that make sense. </p>
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    1. COThank you for the answer. 1. shorter: I meant that the call in controler layer is shorter. 2. encapsulated: controler layer cannot interfere with data logic, won't pass wrong data to a function. 3. the same as 2. The kind of methods I showed here, work on class members only so it's ok I guess
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    2. CO@Chriss: It's not shorter. It's the same. You have to prepare two instance variables or two argument values. The instance variable setup is a critical part of the call -- you can't ignore it.
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    3. CO@Chriss: Nothing prevents passing wrong data to a function. You can set the instance variables incorrectly just as often as you provide wrong function-call argument values.
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Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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