第十一章 赋值表达式和打印

Posted 2020-09-06

#1.
#A:赋值的形式
a, b, c = "szn"             #序列赋值运算 a = ‘s‘ b = ‘z‘ c = ‘n‘
[value0, value1] = [1, 2]   #列表赋值运算 value0 = 1 value1 = 2
value0, value1 = ‘a‘, ‘b‘   #元组赋值运算 value0 = ‘a‘ value1 = ‘b‘
value0, *value1 = "string"  #扩展的序列解包 value0 = ‘s‘ value1 = [‘t‘, ‘r‘, ‘i‘, ‘n‘, ‘g‘]
value0, *value1, value2 = "string"  #value0 = ‘s‘ value1 = [‘t‘, ‘r‘, ‘i‘, ‘n‘] value2 = ‘g‘ 不管带星号的名称出现在哪里，包含该位置的每个未赋值名称的一个列表都将赋给它
value0, *value1 = "12"      #value0 = ‘1‘ value1 = [‘2‘] 带星号的名称可能只匹配单个的项，但是，总会向其赋值一个列表
value0, *value1 = "1"       #value0 = ‘1‘ value1 = []
#*value0 = "ss"             #运行出错 如果有多个带星号的名称，或者值少了而没有带星号的名称，以及如果带星号的名称自身没有编写到一个列表中，都将引发错误
*value0, = "ss"             #value0 = [‘s‘, ‘s‘]
s0 = s1 = [1, 2]            #多目标赋值运算 s0 = [1, 2] s1 = [1, 2]
s0.append(‘s‘)              #s1 = [1, 2, ‘s‘]
a, b, c = range(3)          #a = 0 b = 1 c = 2

#2.
#A:序列赋值语句实际上支持任何可迭代的对象，而不是局限于任何序列
#B:python不支持++ -- 运算符，因为python没有像对数字那样不可变对象进行在原处修改的概念
[a, b, c] = (1, 2, 3)       #a = 1 b = 2 c = 3
(d, e, f) = "abc"           #d = ‘a‘ e = ‘b‘ f = ‘c‘
#(d, e, f) = "abcd"         #运行出错 虽然可以在等号两侧混合相匹配的序列类型，但是右边元素的数目还是要和左边的变量数目相同的，否则会产生错误
string = "abcd"
a, b, c = list(string[:2]) + [string[2:]]   #a = ‘a‘ b = ‘b‘ c = ‘cd‘
((a, b), c) = ("ab", "cd")  #a = ‘a‘ b = ‘b‘ c = ‘cd‘
for ((a, b), c) in [((1, 2), 3), ((‘a‘, ‘b‘), ‘c‘)]:
    print(str(a) + " " + str(b) + " " + str(c), end = ‘ ‘)  #1 2 3 a b c

#3.
#A:+总是生成新对象，而+=是在原处进行修改，其他比如-= *= 均类似
list0 = [1]
list1 = list0
list0 = list0 + [2]         #list0 = [1, 2] list1 = [1]

list0 = [1]
list1 = list0
list0 *= 2                  #list0 = [1, 1] list1 = [1, 1]

#4.
#A:print([object, ...][, sep = ‘ ‘][, end = ‘\n‘][, file = sys.stdout][, flush = False])
#B:printf第一个参数会接收多个待打印值，第二个参数为文本之间的插入字符串，默认为一个空格，第三个参数为换行符，默认为\n，第四个参数是文本将要发送的地方，第五个参数代表是否需要刷新缓冲
print()
import sys
print("s0", ‘s1‘, ‘s2‘, sep = ‘v‘, end = ‘‘, file = sys.stdout, flush = True)   #s0vs1vs2v
MyFile = open(‘1.txt‘, ‘w‘)
print(1 + 2, [1, 2, {3}], sep = ‘sep‘, end = ‘end‘, file = MyFile)    #文件1.txt中写入3sep[1, 2, {3}]end