python中的真假值:
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:
效果:
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