Is Python a

Naming conventionsBesides these rules, there is also a set of naming conventions—rules that are notrequired, but are followed in normal practice. For instance, because names with twoleading and trailing underscores (e.g., _ _name_ _) generally have special meaning tothe Python interpreter, you should avoid this pattern for your own names. Here is alist of the conventions Python follows:• Names that begin with a single underscore (_X) are not imported by a frommodule import * statement (described in Chapter 19).• Names that have two leading and trailing underscores (__X__) are systemdefinednames that have special meaning to the interpreter.• Names that begin with two underscores, and do not end with two more (__X)are localized (“mangled”) to enclosing classes (described in Chapter 26).• The name that is just a single underscore (_) retains the result of the last expressionwhen working interactively.In addition to these Python interpreter conventions, there are various other conventionsthat Python programmers usually follow as well. For instance, later in thebook, we’ll see that class names commonly start with an uppercase letter, and modulenames with a lowercase letter, and that the name self, though not reserved, usuallyhas a special role in classes. In Part IV, we’ll also study another, larger categoryof names known as the built-ins, which are predefined, but not reserved (and so canbe reassigned: open = 42 works, though sometimes you might wish it didn’t!).Names have no type, but objects doThis is mostly review, but remember that it’s crucial to keep Python’s distinctionbetween names and objects clear. As described in “The Dynamic Typing Interlude”in Chapter 6, objects have a type (e.g., integer, list), and may be mutable or not.Names (a.k.a. variables), on the other hand, are always just references to objects;they have no notion of mutability, and have no associated type information, apartfrom the type of the object they happen to reference at a given point in time.It’s OK to assign the same name to different kinds of objects at different times:>>> x = 0 # x bound to an integer object>>> x = "Hello" # Now it's a string>>> x = [1, 2, 3] # And now it's a listIn later examples, you’ll see that this generic nature of names can be a decidedadvantage in Python programming. * In Part IV, you’ll learn that names also live insomething called a scope, which defines where they can be used; the place where youassign a name determines where it is visible.* If you’ve used C++, you may be interested to know that there is no notion of C++’s const declaration inPython; certain objects may be immutable, but names can always be assigned. Python also has ways to hidenames in classes and modules, but they’re not the same as C++’s declarations.Assignment Statements | 227