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 <條件>：
<內容>
2.if
語句流程分支的條件控制，一般和elif和else使用。
x=int(input('请输入一个数字：'))
while x>0:
print('正数')
break3.for語句
#循環控制語句，可用來遍歷某一對象，和in一起使用。 格式： 【 for <> in <物件集合>:】
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')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) # default5.break和
continue
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)登入後複製
2）continue
表示迴圈繼續執行下一個迭代:while True:
print('hello')
break登入後複製
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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