As a Java programmer learning Python, what should I look out for? [closed]

• Don't put everything into classes. Python's built-in list and dictionaries will take you far.
• Don't worry about keeping one class per module. Divide modules by purpose, not by class.
• Use inheritance for behavior, not interfaces. Don't create an "Animal" class for "Dog" and "Cat" to inherit from, just so you can have a generic "make_sound" method.

Just do this:

class Dog(object):
    def make_sound(self):
        return "woof!"

class Cat(object):
    def make_sound(self):
        return "meow!"

class LolCat(object):
    def make_sound(self):
        return "i can has cheezburger?"

The referenced article has some good advice that can easily be misquoted and misunderstood. And some bad advice.

Leave Java behind. Start fresh. "do not trust your [Java-based] instincts". Saying things are "counter-intuitive" is a bad habit in any programming discipline. When learning a new language, start fresh, and drop your habits. Your intuition must be wrong.

Languages are different. Otherwise, they'd be the same language with different syntax, and there'd be simple translators. Because there are not simple translators, there's no simple mapping. That means that intuition is unhelpful and dangerous.

• "A static method in Java does not translate to a Python classmethod." This kind of thing is really limited and unhelpful. Python has a staticmethod decorator. It also has a classmethod decorator, for which Java has no equivalent.

  This point, BTW, also included the much more helpful advice on not needlessly wrapping everything in a class. "The idiomatic translation of a Java static method is usually a module-level function".

• The Java switch statement in Java can be implemented several ways. First, and foremost, it's usually an if elif elif elif construct. The article is unhelpful in this respect. If you're absolutely sure this is too slow (and can prove it) you can use a Python dictionary as a slightly faster mapping from value to block of code. Blindly translating switch to dictionary (without thinking) is really bad advice.

• Don't use XML. Doesn't make sense when taken out of context. In context it means don't rely on XML to add flexibility. Java relies on describing stuff in XML; WSDL files, for example, repeat information that's obvious from inspecting the code. Python relies on introspection instead of restating everything in XML.

  But Python has excellent XML processing libraries. Several.

• Getters and setters are not required in Python they way they're required in Java. First, you have better introspection in Python, so you don't need getters and setters to help make dynamic bean objects. (For that, you use collections.namedtuple).

  However, you have the property decorator which will bundle getters (and setters) into an attribute-like construct. The point is that Python prefers naked attributes; when necessary, we can bundle getters and setters to appear as if there's a simple attribute.

  Also, Python has descriptor classes if properties aren't sophisticated enough.

• Code duplication is often a necessary evil in Java (e.g. method overloading), but not in Python. Correct. Python uses optional arguments instead of method overloading.

  The bullet point went on to talk about closure; that isn't as helpful as the simple advice to use default argument values wisely.

One thing you might be used to in Java that you won't find in Python is strict privacy. This is not so much something to look out for as it is something not to look for (I am embarrassed by how long I searched for a Python equivalent to 'private' when I started out!). Instead, Python has much more transparency and easier introspection than Java. This falls under what is sometimes described as the "we're all consenting adults here" philosophy. There are a few conventions and language mechanisms to help prevent accidental use of "unpublic" methods and so forth, but the whole mindset of information hiding is virtually absent in Python.