cmath.acos(x) Return the arc cosine of x. There are two branch cuts: One extends right from 1 along the real axis to ∞, continuous from below. The other extends left from -1 along the real axis to -∞, continuous from above.

classmethod(function) Return a class method for function. A class method receives the class as implicit first argument, just like an instance method receives the instance. To declare a class method, use this idiom: class C: @classmethod def f(cls, arg1, arg2, ...): ... The @classmethod form is a function decorator – see the description of function definitions in Function definitions for details. It can be called either on the class (such as C.f()) or on an instance (such as C().f())

class.__subclasses__() Each class keeps a list of weak references to its immediate subclasses. This method returns a list of all those references still alive. Example: >>> int.__subclasses__() [<class 'bool'>]

class.__mro__ This attribute is a tuple of classes that are considered when looking for base classes during method resolution.

class.__bases__ The tuple of base classes of a class object.

class.mro() This method can be overridden by a metaclass to customize the method resolution order for its instances. It is called at class instantiation, and its result is stored in __mro__.

tell() Return the current position into the chunk.

skip() Skip to the end of the chunk. All further calls to read() for the chunk will return b''. If you are not interested in the contents of the chunk, this method should be called so that the file points to the start of the next chunk.

seek(pos, whence=0) Set the chunk’s current position. The whence argument is optional and defaults to 0 (absolute file positioning); other values are 1 (seek relative to the current position) and 2 (seek relative to the file’s end). There is no return value. If the underlying file does not allow seek, only forward seeks are allowed.

read(size=-1) Read at most size bytes from the chunk (less if the read hits the end of the chunk before obtaining size bytes). If the size argument is negative or omitted, read all data until the end of the chunk. An empty bytes object is returned when the end of the chunk is encountered immediately.