[Python]格式化输出（2）

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本文详细介绍了Python中各种数据类型及复杂对象的格式化输出方法，包括整型、浮点型数字的格式化，字典类型输出，对象属性值输出，日期时间格式化等，并展示了如何通过参数化进行更灵活的格式控制。

Python版本：Python 2.7.13rc1

1.数字

整型

正确的写法：

>>> print 'The value of PI is approximately %d ' % (3)
The value of PI is approximately 3 
>>> print 'The value of PI is approximately {:d} '.format(3)
The value of PI is approximately 3 
>>> print 'The value of PI is approximately %d ' % (3.1415926)
The value of PI is approximately 3

错误的写法：

>>> print 'The value of PI is approximately {:d} '.format(3.1415926)

对齐：

>>> print '%4d'%(42)
  42
>>> print '{:_>4d}'.format(42)
__42
>>> print '%04d'%(42)
0042
>>> print '{:04d}'.format(42)
0042

浮点型

>>> import math
>>> print 'The value of PI is approximately %f ' % (math.pi)
The value of PI is approximately 3.141593 
>>> print 'The value of PI is approximately {:f} '.format(math.pi)
The value of PI is approximately 3.141593

保留小数点后三位：

>>> print 'The value of PI is approximately %.3f ' % (math.pi)
The value of PI is approximately 3.142 
>>> print 'The value of PI is approximately {:.3f} '.format(math.pi)
The value of PI is approximately 3.142

显示六个字符，其中包括小数点和小数点后三位，不足六个字符补0：

>>> print 'The value of PI is approximately %06.3f ' % (math.pi)
The value of PI is approximately 03.142 
>>> print 'The value of PI is approximately {:06.3f} '.format(math.pi)
The value of PI is approximately 03.142

有正负号的数字

>>> print '%+d' % (42)
+42
>>> print '{:+d}'.format(42)
+42
>>> print '% d' % (-42)
-42
>>> print '{: d}'.format(-42)
-42
>>> print '% d' % (42)
 42
>>> print '{: d}'.format(42)
 42
>>> print '{:=5d}'.format((-42))
-  42

2.Dict类型的格式化输出

根据key取value：

>>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678}
>>> print '%(Sjoerd)d %(Jack)d %(Dcab)d' % table
4127 4098 7678
>>> print '{Sjoerd} {Jack} {Dcab}'.format(**table)
4127 4098 7678
>>> print '{t[Sjoerd]} {t[Jack]} {t[Dcab]}'.format(t=table)
4127 4098 7678

Dict遍历：

>>> for name, ID in table.items():
    print '{0:10} ==> {1:10d}'.format(name,ID)

Dcab       ==>       7678
Jack       ==>       4098
Sjoerd     ==>       4127
>>> for name, ID in table.items():
    print '{1:<10d} ==> {0:>10}'.format(name,ID)

7678       ==>       Dcab
4098       ==>       Jack
4127       ==>     Sjoerd

List 取值：

>>> table2 = ["Sjoerd","Jack","Dcab"]
>>> print '{t[0]} {t[2]}'.format(t=table2)
Sjoerd Dcab

3.输出对象的属性值

>>> class Plant(object):
    type = 'tree'
    kinds = [{'name':'oak'},{'name':'maple'}]


>>> print '{p.type}: {p.kinds[0][name]}'.format(p=Plant())
tree: oak

4.Datetime

>>> from datetime import datetime
>>> dt = datetime(2001, 2, 3, 4, 5)
>>> print '{:%Y-%m-%d %H:%M}'.format(dt)
2001-02-03 04:05
>>> print '{:{dfmt} {tfmt}}'.format(dt, dfmt='%Y-%m-%d', tfmt='%H:%M')
2001-02-03 04:05

5.参数化的格式

设置参数精度：

>>> print '%.*s = %.*f' % (3, 'Gibberish', 3, 2.7182)
Gib = 2.718
>>> print '{:.{prec}} = {:.{prec}f}'.format('Gibberish', 2.7182, prec=3)
Gib = 2.718

参数位置：

>>> print '{:{}{sign}{}.{}}'.format(2.7182818284, '>', 10, 3, sign='+')
     +2.72

6.重写format类

>>> class HAL9000(object):

    def __format__(self, format):
        if (format == 'open-the-pod-bay-doors'):
            return "I'm afraid I can't do that."
        return 'HAL 9000'

>>> print '{:open-the-pod-bay-doors}'.format(HAL9000())
I'm afraid I can't do that.