python开发_python中的Boolean运算和真假值
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python中的真假值：
Any object can be tested truth value, use an condition 1.None
2.False 3.zero of any numeric type, <span style="color: #0000ff;">for example,0.0<span style="color: #000000;">,0j.4.any empty sequence,<span style="color: #800000;">'' <span style="color: #000000;">,(),[].5.any empty mapping, <span style="color: #0000ff;">for<span style="color: #000000;"> example,{}.6.instances of user -defined classes,<span style="color: #0000ff;">if the <span style="color: #0000ff;">class defines a <span style="color: #800080;">bool() <span style="color: #0000ff;">or <span style="color: #800080;">len() method,when that method returns the integer zero <span style="color: #0000ff;">or bool value False. [1<span style="color: #000000;">]All other values are considered true — so objects of many types are always true. Operations <span style="color: #0000ff;">and built-<span style="color: #0000ff;">in functions that have a Boolean result always <span style="color: #0000ff;">return 0 <span style="color: #0000ff;">or False <span style="color: #0000ff;">for false <span style="color: #0000ff;">and 1 <span style="color: #0000ff;">or True <span style="color: #0000ff;">for true,unless otherwise stated. (Important exception: the Boolean operations <span style="color: #0000ff;">or <span style="color: #0000ff;">and <span style="color: #0000ff;">and always <span style="color: #0000ff;">return one of their operands.) 总结：
( if x is false,then y,else x x,y = 2 (.format(x,y,x x1,y1 = 0,10
(.format(x1,y1,x1 x2,y2 = (.format(x2,y2,x2
( * 50 ( if x is false,then x,else y (.format(x,x x1,10
(.format(x1,x1 x2,0
(.format(x2,x2
( * 50 ( if x is false,then True,else False x = 2
(.format(x, x = (.format(x, x))
Python 3.3.2 (v3.3.2:d047928ae3f6,May 16 2013,00:03:43) [MSC v.1600 32, >>> ================================ RESTART ================================
>>> y -> x false,2 0 = 2 10 = 10 0 =
x y -> x false,2 0 = 10 = 0 =
x -> x false, 2 = 0 =>>>
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