Monday 14 October 2019, by Ellie Coverdale
Python is very an extremely attractive option for Rapid Application Development for a lot of different reasons, including the fact that it has high-level built in data structures, dynamic typing and binding, and it can be used to bind different components. Unfortunately, sometimes because it’s so simple and easy to learn, it means that new Python developers stumble on certain subtleties. Read on for the 6 most frequent mistakes that can be difficult to spot but that even Python developers with years of experience have made.
1. Using expressions as defaults for function argument
Python lets developers indicate function arguments that are option through assigning default values. Most of the time, this is one of the reasons Python is so great, but it can cause some confusion when the default value is mutable. The mistake many developers make here is thinking that the optional argument will be the default value that you’ve set each time there is a function argument presented without a value. This can appear to be complicated, but in reality, what happens is that the default value for this function argument is only evaluated when you define the function, and only that one time.
2. Improperly using class variables
The way Python manages its class variables is internally as dictionaries that follow the Method Resolution Order (MRO). As per Johnny Woods, a tech writer at UK Writings and Australian Help, “if an attribute is not located in one class, the system will look it up in the base classes, so the references to a certain part of the code are in reality references to another part, and that can be quite hard for someone to manage in Python. In terms of class attributes, I recommend that developers read up on this part of Python independently to be able to handle them.”
Another problem with the variables is when it comes to binding them in closures. There is a late binding behavior in Python that looks up the value of a variable in closure, but only when calling the inner function. To fix this, it’s possible that you have to use default arguments in your favor to create anonymous functions. This is a work around that will give you the behavior you want.
3. The wrong parameter specifications for exception blocks
A frequent problem in Python is when there are except statements given but they disregard the list of specified exceptions. The syntax Exception is what programmers use to bind exception blocks to certain optional parameters in order to get more inspections. Instead, though, what can happen is that some exceptions will not get linked by the except statement, but the exception is tied to its parameters. To get around this and block exceptions all in one except statement is done by specifying the first parameter as a tuple which will contain all the exceptions that need to be caught.
4. Not understanding scope rules
The scope resolution on Python is founded on the LEGB rule, as we know it, and that means Local, Enclosing, Global, Built-in. Initially this appears simple, however there are some subtleties around how it really works in Python, creating a more complex Python problem. By making an assignment to a variable in scope, Python will take for granted that the variable is local and will copy a variable that’s named the same in other scopes. This problem is particularly troublesome when using lists.
6. Name clash with Python standard library
Python has loads of library modules, and this is a good thing about this language, but it does come with some problems. In this case, you can by accident have a name clash between your own module and a module that exists in the standard library. As per Marian Fairlea, a developer at Essay Roo and OX Essays, “the problem here is importing another library accidentally, and this will import the wrong version. Developers must be aware of the names in the standard library modules and avoid using them to stay away from this problem.”
Python is an excellent language that’s flexible and very powerful; it’s overall a great language for developers and programmers. However, it’s important to be familiar with the intricacies of it to be able to avoid common errors that occur.