实现range类

KeyError

>>> #shell
>>> help(range)
Help on class range in module builtins:

class range(object)
 |  range(stop) -> range object
 |  range(start, stop[, step]) -> range object
 |  
 |  Return an object that produces a sequence of integers from start (inclusive)
 |  to stop (exclusive) by step.  range(i, j) produces i, i+1, i+2, ..., j-1.
 |  start defaults to 0, and stop is omitted!  range(4) produces 0, 1, 2, 3.
 |  These are exactly the valid indices for a list of 4 elements.
 |  When step is given, it specifies the increment (or decrement).
 |  
 |  Methods defined here:
 |  
 |  __bool__(self, /)
 |      self != 0
 |  
 |  __contains__(self, key, /)
 |      Return key in self.
 |  
 |  __eq__(self, value, /)
 |      Return self==value.
 |  
 |  __ge__(self, value, /)
 |      Return self>=value.
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __getitem__(self, key, /)
 |      Return self[key].
 |  
 |  __gt__(self, value, /)
 |      Return self>value.
 |  
 |  __hash__(self, /)
 |      Return hash(self).
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __le__(self, value, /)
 |      Return self<=value.
 |  
 |  __len__(self, /)
 |      Return len(self).
 |  
 |  __lt__(self, value, /)
 |      Return self<value.
 |  
 |  __ne__(self, value, /)
 |      Return self!=value.
 |  
 |  __reduce__(...)
 |      Helper for pickle.
 |  
 |  __repr__(self, /)
 |      Return repr(self).
 |  
 |  __reversed__(...)
 |      Return a reverse iterator.
 |  
 |  count(...)
 |      rangeobject.count(value) -> integer -- return number of occurrences of value
 |  
 |  index(...)
 |      rangeobject.index(value) -> integer -- return index of value.
 |      Raise ValueError if the value is not present.
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  start
 |  
 |  step
 |  
 |  stop
>>> 

所以，我们今天来实现range类的基本功能

根据小甲鱼老师的生成器，代码显而易见

>>> class range:
    def __init__(self, stop, /):
        self.stop = stop
        self.num = -1
    def __iter__(self):
        return self
    def __next__(self):
        self.num += 1
        if self.num >= self.stop:
            raise StopIteration
        return self.num
>>> 

但是这样并不能传入开始值和步长

问题是如果只有一个参数，它应该是结束值，但有两个及以上，应该按开始值，结束值，步长的顺序传入。

两千年后，我终于想到了办法！

class range:
    def __init__(self, *args, /):
        if len(args) == 1:
            self.stop = args[0]
            self.num = -1
            self.add = 1
        elif len(args) == 2:
            self.stop = args[1]
            self.num = args[0] - 1
            self.add = 1
         elif len(args) == 3:
            self.stop = args[1]
            self.num = args[0] - 1
            self.add = args[2]
         elif len(args) == 0:
            raise TypeError("range expected at 1 argument, got 0")
         else:
            raise TypeError(f"range expexct ed at 3 argument, got {len(args)}")
    def __iter__(self):
        return self
    def __next__(self):
        self.num += self.add
        if self.num >= self.stop:
            raise StopIteration
        return self.num
>>> 

>>> for i in range(1, 10, 2):
        print(i)

1
3
5
7
9
>>> 

完美！

match123_xbd