格式化（Formatting）

目录

• 字符串中占位符type
• format

print style
老式的类似C语言风格的格式化输出

用 "%" 来作为占位符

>>> 'i am %s' % ('jiangds')    # 可以采用元组的方式
'i am jiangds'
>>> 'i am %(name)s' % {'name':'jiangds'}    # 可以采用字典的方式
'i am jiangds'
>>> 'i am %s, my name is %s' % ('jcds', 'cm')    # 多次出现采用元组的方式
'i am jcds, my name is cm'
>>> 'i am %(name)s, my name is %(name)s' % {'name':'jiangds'}    # 多次出现采用字典的方式
'i am jiangds, my name is jiangds'
>>> 'i am %(name)s, my name is %(name_2)s' % {'name':'jiangds', 'name_2':'cm'}
'i am jiangds, my name is cm'
>>> name = 'jiangds'
>>> 'i am %s' % name    # 只有一个元素可以直接跟在百分号后面，这里解释其自动做了一个封包，把name封包为元组（语法糖）
'i am jiangds'

字符串中占位符type

部分常用的如下：
|Type |意义 |
---|:--|---
|d、i、u |十进制整数
|d、i、u |十进制整数
|x、X |十六进制整数（x为对应数字里的字母为小写，X为大写）
|e、E |科学计数法（e为对应科学计数里的小写e，E为大写E）
|f、F |浮点数（默认保留6位小数）
|g、G |自动选择最优表示法（整数、浮点数或科学计数法）
|c |单个字符或整数转化为字符
|s |用str()转化的字符串
|r |用repr()转化的字符串
|a |用ascii()转化为字符串
其中的str()和repr()调用的是_str_和_repr_的魔术方法

• 示例

>>> 'the num is %d' % 1211
'the num is 1211'
>>> 'the num is %i' % 1211
'the num is 1211'
>>> 'the num is %u' % 1211
'the num is 1211'
>>> 'the num is %o' % 1211
'the num is 2273'
>>> 'the num is %x' % 1211
'the num is 4bb'
>>> 'the num is %X' % 1211
'the num is 4BB'
>>> 'the num is %e' % 1211
'the num is 1.211000e+03'
>>> 'the num is %E' % 1211
'the num is 1.211000E+03'
>>> 'the num is %f' % 0.123456789
'the num is 0.123457'
>>> 'the num is %F' % 0.123456789
'the num is 0.123457'
>>> 'the num is %g' % 0.123456789
'the num is 0.123457'
>>> 'the num is %g' % 0.00000123456789
'the num is 1.23457e-06'
>>> 'the num is %G' % 0.00000123456789
'the num is 1.23457E-06'
>>> 'the num is %s' % 'jiangds'
'the num is jiangds'
>>> 'the num is %r' % 'jiangds'
"the num is 'jiangds'"
>>> 'the num is %a' % '东升'
"the num is '\\u4e1c\\u5347'"

• 数字的位数和对齐

    -：左对齐
    +：右对齐
    0：填充0

>>> '%0.3f' % 0.123456789    # 小数位保留3位
'0.123'
>>> '%10.3f' % 0.123456789    # 总位数为10位，小数位保留3位，不够空格填充
'     0.123'
>>> '%-10.3f' % 0.123456789    # 总位数10位，"-"左对齐，右边填充空格
'0.123     '
>>> '%+10.3f' % 0.123456789    
'    +0.123'
>>> '%+10.3f' % -0.123456789
'    -0.123'
>>> '%010.3f' % 0.123456789    # 前面加0填充
'000000.123'

format

python3推荐format格式的格式化输出，功能更强大

字符串中的占位符用 {} 或者带索引的 {Index} ， 或者更详细的格式（索引后面加冒号），如{0:10.3f}等。

format括号里可以跟位置参数，也可以跟关键字参数。

• 示例

>>> 'i am {}'.format('jds')
'i am jds'
>>> 'i am {}, my age is {}'.format('jds', '18')
'i am jds, my age is 18'
>>> 'i am {1}, my age is {0}'.format('18', 'jds')
'i am jds, my age is 18'
>>> 'i am {name}, my age is {age}'.format(name='jds', age=18)
'i am jds, my age is 18'
>>> 'i am {name}, my name is {name}'.format(name='jds')
'i am jds, my name is jds'
>>> 'i am {0}, my name is {0}'.format('jds')
'i am jds, my name is jds'