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This "underscoring" seems to occur a lot, and I was wondering if this was a requirement in the Python language, or merely a matter of convention?
Also, could someone name and explain which functions tend to have the underscores, and why (__init__, for instance)?
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A single leading underscore in front of a variable, a function, or a method name means that these objects are used internally. This is more of a syntax hint to the programmer and is not enforced by the Python interpreter which means that these objects can still be accessed in one way on another from another script.
The use of double underscore ( __ ) in front of a name (specifically a method name) is not a convention; it has a specific meaning to the interpreter. Python mangles these names and it is used to avoid name clashes with names defined by subclasses.
Single Underscore In a class, names with a leading underscore indicate to other programmers that the attribute or method is intended to be be used inside that class. However, privacy is not enforced in any way. Using leading underscores for functions in a module indicates it should not be imported from somewhere else.
A double underscore prefix causes the Python interpreter to rewrite the attribute name in order to avoid naming conflicts in subclasses. This is also called name mangling—the interpreter changes the name of the variable in a way that makes it harder to create collisions when the class is extended later.
From the Python PEP 8 -- Style Guide for Python Code:
Descriptive: Naming Styles
The following special forms using leading or trailing underscores are recognized (these can generally be combined with any case convention):
_single_leading_underscore: weak "internal use" indicator. E.g.from M import *does not import objects whose name starts with an underscore.
single_trailing_underscore_: used by convention to avoid conflicts with Python keyword, e.g.
Tkinter.Toplevel(master, class_='ClassName')
__double_leading_underscore: when naming a class attribute, invokes name mangling (inside class FooBar,__boobecomes_FooBar__boo; see below).
__double_leading_and_trailing_underscore__: "magic" objects or attributes that live in user-controlled namespaces. E.g.__init__,__import__or__file__. Never invent such names; only use them as documented.
Note that names with double leading and trailing underscores are essentially reserved for Python itself: "Never invent such names; only use them as documented".
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