list

[hug2wisdom]

shallow copy(浅复制)

cubes = [1, 2, 4]
new_cubes = cubes[:]
print(new_cubes)
print(cubes)

# the result:
[1, 2, 4]
[1, 2, 4]

clear the list:

cubes = [1, 2, 4]
cubes[:] = []
print(cubes)

# the result
[]

[hug2wisdom]

想要在循环中修改 list 中的 items 时，需要在 for 语句中使用 list 的切片，即 list[:] ，原因是，如果直接用 for item in list[] 的话，会造成无限循环。

If you need to modify the sequence you are iterating over while inside the loop (for example to duplicate selected items), it is recommended that you first make a copy. Iterating over a sequence does not implicitly make a copy. The slice notation makes this especially convenient.

[hug2wisdom]

You might have noticed that methods like insert, remove or sort that only modify the list have no return value printed – they return the default None. This is a design principle for all mutable data structures in Python.

[hug2wisdom]

Note that in Python, unlike C, assignment cannot occur inside expressions. C programmers may grumble about this, but it avoids a common class of problems encountered in C programs: typing = in an expression when == was intended.

需要注意的是Python与C不同，在表达式内部不能赋值。C 程序员经常对此抱怨，不过它避免了一类在 C 程序中司空见惯的错误：想要在解析式中使 == 时误用了 = 操作符。

a = b + c
左边 a 表示变量 variable ， 右边 b + c 表示表达式， 而表达式里不能赋值，即不能出现：a = b == 1 + c == 2

[hug2wisdom]

通过列表来进行反转字符串

def reverseWords(input): 
      
    # 通过空格将字符串分隔符，把各个单词分隔为列表
    inputWords = input.split(" ") 
  
    # 翻转字符串
    # 假设列表 list = [1,2,3,4],  
    # list[0]=1, list[1]=2 ，而 -1 表示最后一个元素 list[-1]=4 ( 与 list[3]=4 一样) 
    # inputWords[-1::-1] 有三个参数
    # 第一个参数 -1 表示最后一个元素
    # 第二个参数为空，表示移动到列表末尾
    # 第三个参数为步长，-1 表示逆向
    inputWords=inputWords[-1::-1] 
  
    # 重新组合字符串
    output = ' '.join(inputWords) 
      
    return output 
  
if __name__ == "__main__": 
    input = 'I like runoob'
    rw = reverseWords(input) 
    print(rw)

# result 
runoob like I

[hug2wisdom]

list.index(x)	返回列表中第一个值为 x 的元素的索引。如果没有匹配的元素就会返回一个错误。

list.copy()	返回列表的浅复制，等于a[:]