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详解Python中的元组与逻辑运算符

yipeiwu_com6年前 (2020-03-06)Python基础

Python元组
元组是另一个数据类型，类似于List（列表）。
元组用"()"标识。内部元素用逗号隔开。但是元素不能二次赋值，相当于只读列表。

#!/usr/bin/python
# -*- coding: UTF-8 -*-

tuple = ( 'abcd', 786 , 2.23, 'john', 70.2 )
tinytuple = (123, 'john')

print tuple # 输出完整元组
print tuple[0] # 输出元组的第一个元素
print tuple[1:3] # 输出第二个至第三个的元素 
print tuple[2:] # 输出从第三个开始至列表末尾的所有元素
print tinytuple * 2 # 输出元组两次
print tuple + tinytuple # 打印组合的元组

以上实例输出结果：

('abcd', 786, 2.23, 'john', 70.2)
abcd
(786, 2.23)
(2.23, 'john', 70.2)
(123, 'john', 123, 'john')
('abcd', 786, 2.23, 'john', 70.2, 123, 'john')

以下是元组无效的，因为元组是不允许更新的。而列表是允许更新的：

#!/usr/bin/python
# -*- coding: UTF-8 -*-

tuple = ( 'abcd', 786 , 2.23, 'john', 70.2 )
list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]
tuple[2] = 1000 # 元组中是非法应用
list[2] = 1000 # 列表中是合法应用

Python逻辑运算符
Python语言支持逻辑运算符，以下假设变量a为10，变量b为20：

以下实例演示了Python所有逻辑运算符的操作：

#!/usr/bin/python

a = 10
b = 20
c = 0

if ( a and b ):
  print "Line 1 - a and b are true"
else:
  print "Line 1 - Either a is not true or b is not true"

if ( a or b ):
  print "Line 2 - Either a is true or b is true or both are true"
else:
  print "Line 2 - Neither a is true nor b is true"


a = 0
if ( a and b ):
  print "Line 3 - a and b are true"
else:
  print "Line 3 - Either a is not true or b is not true"

if ( a or b ):
  print "Line 4 - Either a is true or b is true or both are true"
else:
  print "Line 4 - Neither a is true nor b is true"

if not( a and b ):
  print "Line 5 - Either a is not true or b is not true or both are not true"
else:
  print "Line 5 - a and b are true"

以上实例输出结果：

Line 1 - a and b are true
Line 2 - Either a is true or b is true or both are true
Line 3 - Either a is not true or b is not true
Line 4 - Either a is true or b is true or both are true
Line 5 - Either a is not true or b is not true or both are not true