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python 字符串格式化代码

Jun 06, 2016 am 11:27 AM
python string format

格式汇总:

格式 描述 格式 描述
%% 百分号%标记(多出来的%是转义作用)    
%c 字符及其ASCII码 %s 字符串
%d 有符号整数(十进制) %u 无符号整数(十进制)
%o 无符号整数(八进制)    
%x 无符号整数(十六进制) %X 无符号整数(十六进制大写字符)
%e 浮点数字(科学计数法) %E 浮点数字(科学计数法,用E代替e)
%f 浮点数字(用小数点符号)    
%g 浮点数字(根据值的不同自动选择%e或%f) %G 浮点数字(类似于%g,根据值的不同自动选择%E或%f)
%p 指针(用十六进制打印值的内存地址) %n 存储输出字符的数量放进参数列表的下一个变量中

不过由于在python中,所有东西都可以转换成string类型,因此,如果没有什么特殊需求完全可以全部使用'%s‘来标记。
比如:'%s %s %s' % (1, 2.3, ['one', 'two', 'three'])
它的输出为'1 2.3 ['one', 'two', 'three']',就是按照%左边的标记输出的。
虽然第一个和第二值不是string类型,一样没有问题。
[在这个过程中,当电脑发现第一个值不是%s时,会先调用整型数的函数,把第一个值也就是1转成string类型,然后再调用str()函数来输出。]

上面说的只是格式标记的最简间的形式,来看复杂一点的:
制定输出长度:
‘%6.2f' % 1.235
在这种形式中,在f的前面出现了一个类似小数的6.2它表示的意思是,总共输出的长度为6个字符,其中小数2位。

还有更复杂的:
占位符:
‘%06.2f' % 1.235
在6的前面多了一个0,表示如果输出的位数不足6位就用0补足6位。
这一行的输出为‘001.24',可以看到小数也占用一位。

类似于这里0这样的标记还有-、+。其中,-表示左对齐,+表示在正数前面也标上+号,默认是不加的。

实例:
%ns:如果字符串变量s不足n位的话,会先输出若干个空格后再输出str1
%-ns:与上述相反,先输出变量s,不足的然后用空格在后面补齐。

其他:
字典格式化输出:
‘%(name)s:%(score)06.1f' %{'score':9.5, 'name':'newsim'}
这种形式只用在要输出的内容为dictionary时。小括号中的(name)和(score)对应于后面的键值对中的键。

有时候在%6.2f这种形式中,6和2也不能事先指定,会在程序运行过程中再产生,那怎么输入呢,当然不能用%%d.%df或%d.%d%f。
可以用%*.*f的形式,当然在后面的”要输出的值组“中包含那两个*的值。
比如:'%*.*f' % (6, 2, 2.345)就相当于'%6.2f' % 2.345。
不过如果记不住,或不想那么耐烦,完全可以全部用%s代替,或者用多个"+"来构造类似的输出字符串。

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