语句

else可选

i = 0while i <= 3:    print("循环{}次".format(i))    i += 1else:    print("结束")

语句

可以有0个或多个 块,，并且 块是可选的

一个 ... ... ...序列 是对其他语言的switch or case 语句的替代方案。

>>> x = int(input("Please enter an integer: "))Please enter an integer: 42>>> if x < 0:...     x = 0...     print('Negative changed to zero')... elif x == 0:...     print('Zero')... elif x == 1:...     print('Single')... else:...     print('More')...More

语句

Python 的 语句可以按照元素出现的顺序迭代任何序列（列表或字符串）

 

>>> # Measure some strings:... words = ['cat', 'window', 'defenestrate']>>> for w in words:...     print(w, len(w))...cat 3window 6defenestrate 12

如果要在循环内修改正在迭代的序列（例如，复制所选的项目），建议首先创建原序列的拷贝

import time words = ['cat', 'window', 'defenestrate'] print(id(words))　　#id()查内存地址 b = words[:] for w in b: # Loop over a slice copy of the entire list. if len(w) > 6: words.insert(0, w) print(id(b),words) time.sleep(1) [:]浅拷贝后内存地址变了 267616368200 267616357448 ['defenestrate', 'cat', 'window', 'defenestrate']

函数

包含起点不包含终点，可以是负数，第三个参数可以指定一个步进值。

由 返回的对象的行为就像它是一个列表，但事实上它不是。它是一个对象。当您遍历它时， 它会返回所需的序列连续项。但它并不真的生成了列表，从而节省了空间

>>> for i in range(5):...     print(i)...01234

range(5, 10) 5 through 9 range(0, 10, 3) 0, 3, 6, 9 range(-10, -100, -30) -10, -40, -70 要迭代序列的索引，您可以将和组合如下：

>>> a = ['Mary', 'had', 'a', 'little', 'lamb'] >>> for i in range(len(a)): ... print(i, a[i]) ... 0 Mary 1 had 2 a 3 little 4 lamb 或者是这样; enumerate(iterable, start=0)

>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter'] >>> list(enumerate(seasons)) [(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')] >>> list(enumerate(seasons, start=1)) [(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]

 

和语句，以及循环中子句

语句用于跳出最近的 或 循环。

循环语句可以有一个 else 子句;当（）循环迭代完整个列表或（）循环条件变为假，而非由语句终止时，就会执行这个else语句。

>>> for n in range(2, 10):...     for x in range(2, n):...         if n % x == 0:...             print(n, 'equals', x, '*', n//x)...             break...     else:...         # loop fell through without finding a factor...         print(n, 'is a prime number')...2 is a prime number3 is a prime number4 equals 2 * 25 is a prime number6 equals 2 * 37 is a prime number8 equals 2 * 49 equals 3 * 3

语句表示继续下一次迭代：

>>> for num in range(2, 10):...     if num % 2 == 0:...         print("Found an even number", num)...         continue...     print("Found a number", num)Found an even number 2Found a number 3Found an even number 4Found a number 5Found an even number 6Found a number 7Found an even number 8Found a number 9

语句

语句什么也不做。当语法上需要语句但程序不需要动作时，可以使用它

>>> while True:...     pass  # Busy-wait for keyboard interrupt (Ctrl+C)...

>>> class MyEmptyClass:...     pass ...

>>> def initlog(*args): ... pass # Remember to implement this! ...