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优点是可以不用库名加点方式运行函数
缺点是不同库之间函数名和用户自定义函数名会冲突。
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0x,0X开头为16进制
0b,0B开头为2进制
0o,0O开头为8进制
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整数是特殊的小数,小数是特殊的复数。
\n 换行
元祖外侧可以使用负号也可以不使用,除非元祖中有元祖元素。
元祖不能更改也不能删除。
finally 不管前面条件如何也要执行。
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ctrl+c终止死循环执行
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python浮点型精度
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只有python有复数类型
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三单引号不是注释,是字符串,没有赋值变量,系统不运行,达到注释效果。
三引号中可以存在双引号和单引号。
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a.b是面向对象思想,a是对象,b是a对象提供的方法 。
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第一个:0为槽的位置,等号为填充符号。^代表居中对齐。20为宽度/长度。
第二个:右对齐。
第三个:默认左对齐。
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第一个:,代表数字用千位符表示。
第二个:b为2进制,c为字符unit编码形式,d为十进制,o为8进制,x十六进制,X大写十进制。
第三个:e科学计数法,E科学计数法,f通常浮点型,%百分号形式。
3.0f表示从小数点左边开始数,3个字符的宽度数据被保留,如果数据超出,按数据的实际长度输出。
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此种方法只支持表达式,不支持赋值语句。
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只有在这种异常情况下,才会执行语句2。
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不发生异常执行语句3,异常执行语句2。
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与异常处理else类似,没有异常,奖励执行else。
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\表示换行
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可选参数必须放在可选参数之后。
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*后面可以是任何字母
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map(a, b)将将a函数作用于b(迭代类型)b中的每个元素用a函数
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除了""、0、()、[]、{}、None为False之外,其他的都是True。
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[图片上传中...(image.png-9dc23d-1543155119729-0)]
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global 只在函数内使用,不在循环中使用。
2个变量赋值: a= 1 b=2错误 a = 1, b = 2也错误。正确时a, b = 1, 2
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l = '12345'
l[-2:]表示按顺序最后两个字符45
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指开头
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可打印用字符表示,不可打印用十六进制表示。
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import from方式导入库 如果名称冲突 以最后声明为准
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int(1.9)=1
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python底层解释器是c语言编写。为了对条件判断更灵活的支持,Flase更多含义。
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异常处理在函数中处理时约定,先执行完finally,再执行return。(也就是执行完finally才能返回)而且finally中的return会替换掉其他return。
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try中有return,else不会执行。
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局部变量叫形参
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大写U
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不但名称,介绍文件中有也会被搜索出来。
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适用于win系统
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换成下载命令,可以获取这些安装包。
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