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Python中使用pprint函数进行格式化输出的教程

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Jun 10, 2016 pm 03:16 PM

python

pprint – 美观打印

作用：美观打印数据结构

pprint 包含一个“美观打印机”，用于生成数据结构的一个美观视图。格式化工具会生成数据结构的一些表示，不仅可以由解释器正确地解析，而且便于人类阅读。输出尽可能放在一行上，分解为多行时则需要缩进。

以下实例用用到的data包含一下数据

data = [(1,{'a':'A','b':'B','c':'C','d':'D'}),

    (2,{'e':'E','f':'F','g':'G','h':'H',

      'i':'I','j':'J','k':'K','l':'L'

      }),

    ]

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1、打印

要使用这个模块，最简单的方法就是利用pprint()函数

from pprint import pprint
print 'PRINT:'
print data
print 
print 'PPRINT:'
pprint(data)

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运行结果：

PRINT:
[(1, {'a': 'A', 'c': 'C', 'b': 'B', 'd': 'D'}), (2, {'e': 'E', 'g': 'G', 'f': 'F', 'i': 'I', 'h': 'H', 'k': 'K', 'j': 'J', 'l': 'L'})]
PPRINT:
[(1, {'a': 'A', 'b': 'B', 'c': 'C', 'd': 'D'}),
 (2,
 {'e': 'E',
  'f': 'F',
  'g': 'G',
  'h': 'H',
  'i': 'I',
  'j': 'J',
  'k': 'K',
  'l': 'L'})]

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pprint()格式化一个对象，并把它写至一个数据流，这个数据流作为参数传入（或者是默认的sys.stdout）

注意为什么第二个字典中会显示一竖列，因为pprint打印支持8个对象以上的竖列打印

2、格式化

格式化一个数据结构而不把它直接写至一个流（例如用于日志记录），可以使用pformat()来构造一个字符串表示。

import logging
from pprint import pformat
logging.basicConfig(level = logging.DEBUG,
          format = '%(levelname)-8s %(message)s',
          )
logging.debug('Logging pformatted data')
formatted = pformat(data)
for line in formatted.splitlines():
  logging.debug(line.rstrip())

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运行结果：

DEBUG  Logging pformatted data
DEBUG  [(1, {'a': 'A', 'b': 'B', 'c': 'C', 'd': 'D'}),
DEBUG   (2,
DEBUG   {'e': 'E',
DEBUG    'f': 'F',
DEBUG    'g': 'G',
DEBUG    'h': 'H',
DEBUG    'i': 'I',
DEBUG    'j': 'J',
DEBUG    'k': 'K',
DEBUG    'l': 'L'})]

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然后可以单独低打印格式化的字符串或者计入日志

splitlines() 按行分割()

rstrip()去除右边的空格 lstrip()去除左边的空格 strip()去除两边空格。默认为去除空格，也可以传入需要从两边或者其中一边去除的字符，如strip(‘a')就是去除字符串两边的字符'a'
3、任意类

如果定制类定义了一个__repr__()方法，pprint()使用的PrettyPrinter类还可以处理这些定制类。

from pprint import pprint 
class node(object):
  def __init__(self,name,contents =[]):
    self.name = name
    self.contents = contents[:]
  def __repr__(self):
    return ('node(' + repr(self.name) + ',' +
        repr(self.contents) + ')'
        )
trees = [node('node-1'),
     node('node-2',[node('node-2-1')]),
     node('node-3',[node('node-3-1')]),     
     ]
pprint(trees)

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运行结果：

[node('node-1',[]),
 node('node-2',[node('node-2-1',[])]),
 node('node-3',[node('node-3-1',[])])]

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由PrettyPrinter组合嵌套对象的表示，从而返回完整字符串表示。
4、递归

递归数据结构有指向原数据源的引用来表示，形式为。

from pprint import pprint 
local_data = ['a','b',1,2]
local_data.append(local_data)
print 'id(local_data) =>',id(local_data)
pprint(local_data)
print local_data

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运行结果：

id(local_data) => 47458332363520
['a', 'b', 1, 2, <Recursion on list with id=47458332363520>]
['a', 'b', 1, 2, [...]]

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在这个例子中，列表local_data增加到了其自身，这会创建一个递归引用

内置函数id()作用是获得对象的id值，理论上讲每个对象都有一个id值，如果是整数和字符串（(相对较小的时候)），那么相同的值会有相同的id值，但是如果是类，及时相同也会有不同的id值。测试如下：

#int or float or lon 都一样(比较小的时候)
a = 65464131311513l
b = 65464131311513l
c = 65464131311513l
print id(a)
print id(b)
print id(c)
print
a = '12312312'
b = '12312312'
c = '12312312'
print id(a)
print id(b)
print id(c)
print 
a = 65464131311513l*11
b = 65464131311513l*11
c = 65464131311513l*11
print id(a)
print id(b)
print id(c)
print
a = '12312312'*11
b = '12312312'*11
c = '12312312'*11
print id(a)
print id(b)
print id(c)
print 
class Test(object):
  def __init__(self):
    pass
a = Test()
b = Test()
c = Test()
print id(a)
print id(b)
print id(c)
print

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测试结果：

47010342174992

47010342174992

47010342174992


47010343272096

47010343272096

47010343272096


47010343261568

47010343261648

47010343261688


47010343200944

47010343199152

47010343202352


47010343252304

47010343252944

47010343253008

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5、限制嵌套输出

对于非常深的数据结构，可能不要求输出包含所有细节。有可能数据没有是当地格式化，也可能格式化文本过大而无法管理，或者默写数据时多余的。

from pprint import pprint 
print 'depth 1 :'
pprint(data,depth=1)
print 
print 'depth 2 :'
pprint(data,depth=2)
print 
print 'depth 3 :'
pprint(data,depth=3)

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运行结果：

depth 1 :
[(...), (...)]
depth 2 :
[(1, {...}), (2, {...})]
depth 3 :
[(1, {'a': 'A', 'b': 'B', 'c': 'C', 'd': 'D'}),
 (2,
 {'e': 'E',
  'f': 'F',
  'g': 'G',
  'h': 'H',
  'i': 'I',
  'j': 'J',
  'k': 'K',
  'l': 'L'})]

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使用depth参数可以控制美观打印机递归处理嵌套数据结构的深度。输出中未包含的层次由一个省略号表示
6、控制输出宽度

格式化文本的默认输出宽度为80列。要调整这个宽度，可以再pprint()中使用参数width。

from pprint import pprint
for width in [80,5]:
  print 'WIDTH = ', width
  pprint(data,width = width)
  print

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运行结果：

WIDTH = 80
[(1, {'a': 'A', 'b': 'B', 'c': 'C', 'd': 'D'}),
 (2,
 {'e': 'E',
  'f': 'F',
  'g': 'G',
  'h': 'H',
  'i': 'I',
  'j': 'J',
  'k': 'K',
  'l': 'L'})]
WIDTH = 5
[(1,
 {'a': 'A',
  'b': 'B',
  'c': 'C',
  'd': 'D'}),
 (2,
 {'e': 'E',
  'f': 'F',
  'g': 'G',
  'h': 'H',
  'i': 'I',
  'j': 'J',
  'k': 'K',
  'l': 'L'})]

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宽度大小不能适应格式化数据结构时，如果斩断或转行会引入非法的语法，就不会进行截断或转行。

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