Python流程控製程式碼詳解

1.while語句

條件循環控制語句。一般需要和break一起使用，不然會進入死循環。

格式：【 while b113cd7a08914f67edf6a268201cfce1：

                 129bbd4349cc9a05cbcadcd386a064d8 in ab1d6c9b5d466dd539b41c59e41bfbb9:】

x=int(input('请输入一个数字：'))
if x<0:
    print(&#39;负数&#39;)
elif x==0:
    print(&#39;零&#39;)
else :
    print(&#39;正数&#39;)

4.

range

()

函數數字序列迭代器,當你迭代它時，它是一個能夠像期望的序列返回連續項的物件,但為了節省空間，它並不真正構造列表。 格式：  range(stop)  給出結束數值，開始數值預設為0，間隔為1。

           range(start,stop)  給予開始數值及結束數值，間隔1。

           range(start,stop,step)  給予開始數值與結束數值，間隔為step數值。

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

5.break和
continue

語句，以及迴圈中的else語句

1）break 語句和

C 中的類似，用來跳出最近的一級for 或while 循環。

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)

2）continue

語句

表示迴圈繼續執行下一個迭代:

while True:
    print('hello')
    break

 3）迴圈中的else

如continue的例子裡，有for-else語句，else語句會在迴圈跳出後執行，但是break跳出迴圈則不會執行else,所以else可以用來處理迴圈中的一些異常跳出。

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

6.pass語句

pass語句什麼都不做。它用於那些語法上必須要有什麼語句，但程式什麼也不做的場合，通常用於創建最小結構的類別。 另一方面，pass可以在建立新程式碼時用來做函數或控制體的佔位符。可以讓你在更抽象的層次上思考。

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

#运行结果
2
3

#

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