Python流程控制代码详解

x=int(input('请输入一个数字：'))
while x>0:
    print('正数')
    break

x=int(input('请输入一个数字：'))
if x<0:
    print('负数')
elif x==0:
    print('零')
else :
    print('正数')

x=['a','b','c','d']for i in x :  
            # i 位置的字符，只要不是关键字，可以随意用字符代表
    print(i)

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).
    """
    def count(self, value): # real signature unknown; restored from doc
        """ rangeobject.count(value) -> integer -- return number of occurrences of value """
        return 0

    def index(self, value, start=None, stop=None): # real signature unknown; restored from doc
        """
        rangeobject.index(value, [start, [stop]]) -> integer -- return index of value.
        Raise ValueError if the value is not present.
        """
        return 0

    def contains(self, *args, **kwargs): # real signature unknown
        """ Return key in self. """
        pass

    def eq(self, *args, **kwargs): # real signature unknown
        """ Return self==value. """
        pass

    def getattribute(self, *args, **kwargs): # real signature unknown
        """ Return getattr(self, name). """
        pass

    def getitem(self, *args, **kwargs): # real signature unknown
        """ Return self[key]. """
        pass

    def ge(self, *args, **kwargs): # real signature unknown
        """ Return self>=value. """
        pass

    def gt(self, *args, **kwargs): # real signature unknown
        """ Return self>value. """
        pass

    def hash(self, *args, **kwargs): # real signature unknown
        """ Return hash(self). """
        pass

    def init(self, stop): # real signature unknown; restored from doc
        pass

    def iter(self, *args, **kwargs): # real signature unknown
        """ Implement iter(self). """
        pass

    def len(self, *args, **kwargs): # real signature unknown
        """ Return len(self). """
        pass

    def le(self, *args, **kwargs): # real signature unknown
        """ Return self<=value. """
        pass

    def lt(self, *args, **kwargs): # real signature unknown
        """ Return self<value. """
        pass

    @staticmethod # known case of new
    def new(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def ne(self, *args, **kwargs): # real signature unknown
        """ Return self!=value. """
        pass

    def reduce(self, *args, **kwargs): # real signature unknown
        pass

    def repr(self, *args, **kwargs): # real signature unknown
        """ Return repr(self). """
        pass

    def reversed(self, *args, **kwargs): # real signature unknown
        """ Return a reverse iterator. """
        pass

    start = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    step = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    stop = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

for i in range(3):          #运行结果为0，1，2
    print(i)
for i in range(0,5):       #运行结果为0，1，2，3，4
    print(i)
for i in range(-2,10,2): #运行结果为-2，0，2，4，6，8
    print(i)

while True:
    print('hello')
    break

for x in range(1, 4):
        print(x, 'for语句')
        continue
        print(x, 'continue语句后')
else:
        print(x, 'else语句')
 
#运行结果
for语句
for语句
for语句
else语句

for x in range(1, 4):
        print(x)
else:
        print(x)

#运行结果
2
3

class EmptyClass：
    pass