BIF(built-in functions) 顾名思义，就是Erlang内建函数。它们通常用来完成那此无法用Erlang完成的任务。比如将列表转换为元组或者获取当前
的时间和日期。完成这些操作的函数，我们称之为BIF。python中提供了大量的内置功能函数，这就意味着你可以少些很多的代码。
我们可以在python或IDLE shell中，键入dir(__builtins__)可以看到python的内置方法列表，"builtins"的前后都是两个下划线，shell会给出一个
庞大的列表，如下：
[‘ArithmeticError‘, ‘AssertionError‘, ‘AttributeError‘, ‘BaseException‘, ‘BlockingIOError‘, ‘BrokenPipeError‘, ‘BufferError‘, ‘BytesWarning‘,
‘ChildProcessError‘, ‘ConnectionAbortedError‘, ‘ConnectionError‘, ‘ConnectionRefusedError‘, ‘ConnectionResetError‘,
‘DeprecationWarning‘, ‘EOFError‘, ‘Ellipsis‘, ‘EnvironmentError‘, ‘Exception‘, ‘False‘, ‘FileExistsError‘, ‘FileNotFoundError‘,
‘FloatingPointError‘, ‘FutureWarning‘, ‘GeneratorExit‘, ‘IOError‘, ‘ImportError‘, ‘ImportWarning‘, ‘IndentationError‘, ‘IndexError‘,
‘InterruptedError‘, ‘IsADirectoryError‘, ‘KeyError‘, ‘KeyboardInterrupt‘, ‘LookupError‘, ‘MemoryError‘, ‘NameError‘, ‘None‘,
‘NotADirectoryError‘, ‘NotImplemented‘, ‘NotImplementedError‘, ‘OSError‘, ‘OverflowError‘, ‘PendingDeprecationWarning‘,
‘PermissionError‘, ‘ProcessLookupError‘, ‘ReferenceError‘, ‘ResourceWarning‘, ‘RuntimeError‘, ‘RuntimeWarning‘, ‘StopIteration‘,
‘SyntaxError‘, ‘SyntaxWarning‘, ‘SystemError‘, ‘SystemExit‘, ‘TabError‘, ‘TimeoutError‘, ‘True‘, ‘TypeError‘, ‘UnboundLocalError‘,
‘UnicodeDecodeError‘, ‘UnicodeEncodeError‘, ‘UnicodeError‘, ‘UnicodeTranslateError‘, ‘UnicodeWarning‘, ‘UserWarning‘,
‘ValueError‘, ‘Warning‘, ‘WindowsError‘, ‘ZeroDivisionError‘, ‘_‘, ‘__build_class__‘, ‘__debug__‘, ‘__doc__‘, ‘__import__‘, ‘__loader__‘,
‘__name__‘, ‘__package__‘, ‘__spec__‘, ‘abs‘, ‘all‘, ‘any‘, ‘ascii‘, ‘bin‘, ‘bool‘, ‘bytearray‘, ‘bytes‘, ‘callable‘, ‘chr‘, ‘classmethod‘, ‘compile‘,
‘complex‘, ‘copyright‘, ‘credits‘, ‘delattr‘, ‘dict‘, ‘dir‘, ‘divmod‘, ‘enumerate‘, ‘eval‘, ‘exec‘, ‘exit‘, ‘filter‘, ‘float‘, ‘format‘, ‘frozenset‘,
‘getattr‘, ‘globals‘, ‘hasattr‘, ‘hash‘, ‘help‘, ‘hex‘, ‘id‘, ‘input‘, ‘int‘, ‘isinstance‘, ‘issubclass‘, ‘iter‘, ‘len‘, ‘license‘, ‘list‘, ‘locals‘, ‘map‘,
‘max‘, ‘memoryview‘, ‘min‘, ‘next‘, ‘object‘, ‘oct‘, ‘open‘, ‘ord‘, ‘pow‘, ‘print‘, ‘property‘, ‘quit‘, ‘range‘, ‘repr‘, ‘reversed‘, ‘round‘, ‘set‘,
‘setattr‘, ‘slice‘, ‘sorted‘, ‘staticmethod‘, ‘str‘, ‘sum‘, ‘super‘, ‘tuple‘, ‘type‘, ‘vars‘, ‘zip‘]
要查看某个BIF是干什么的，可以在shell中键入help(方法名),如， help(isinstance),就会得到这个BIF的功能描述.如下：
>>> help(isinstance)
Help on built-in function isinstance in module builtins:
isinstance(...)
isinstance(object, class-or-type-or-tuple) -> bool
Return whether an object is an instance of a class or of a subclass thereof.
With a type as second argument, return whether that is the object‘s type.
The form using a tuple, isinstance(x, (A, B, ...)), is a shortcut for
isinstance(x, A) or isinstance(x, B) or ... (etc.).
就可以得到isinstance函数的介绍和使用方法。