8.18. pprint — 数据美化打印机 ¶

源代码： Lib/pprint.py

The pprint module provides a capability to “pretty-print” arbitrary Python data structures in a form which can be used as input to the interpreter. If the formatted structures include objects which are not fundamental Python types, the representation may not be loadable. This may be the case if objects such as files, sockets, classes, or instances are included, as well as many other built-in objects which are not representable as Python constants.

格式化表示将对象保持在一行中若可以的话，和将它们分成多行若不拟合允许宽度。构造 PrettyPrinter 对象明确若需要调节宽度约束。

Changed in version 2.5: Dictionaries are sorted by key before the display is computed; before 2.5, a dictionary was sorted only if its display required more than one line, although that wasn’t documented.

2.6 版改变： 添加支持 set and frozenset .

The pprint 模块定义 1 个类：

class pprint. PrettyPrinter ( indent=1 , width=80 , depth=None , stream=None ) ¶

构造 PrettyPrinter 实例。此构造函数理解几个关键词参数。可以设置输出流使用 stream 关键词；用于流对象的唯一方法是文件协议的 write() 方法。若未指定， PrettyPrinter 采纳 sys.stdout . Three additional parameters may be used to control the formatted representation. The keywords are indent , depth ，和 width 。为各递归级别添加缩进的数量指定通过 indent ；默认为 1。其它值可能导致输出看起来有点零散，但可以使嵌套更容易被认出。可打印层数的控制通过 depth ；若正打印数据结构太深，下一包含级别将被替换为 ... 。默认情况下，格式化对象的深度不受约束。期望输出宽度的约束使用 width parameter; the default is 80 characters. If a structure cannot be formatted within the constrained width, a best effort will be made.

>>> import pprint
>>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
>>> stuff.insert(0, stuff[:])
>>> pp = pprint.PrettyPrinter(indent=4)
>>> pp.pprint(stuff)
[   ['spam', 'eggs', 'lumberjack', 'knights', 'ni'],
    'spam',
    'eggs',
    'lumberjack',
    'knights',
    'ni']
>>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead',
... ('parrot', ('fresh fruit',))))))))
>>> pp = pprint.PrettyPrinter(depth=6)
>>> pp.pprint(tup)
('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', (...)))))))
							

The PrettyPrinter class supports several derivative functions:

pprint. pformat ( 对象 , indent=1 , width=80 , depth=None ) ¶

返回格式化表示 object 以字符串形式。 indent , width and depth 会被传递给 PrettyPrinter 构造函数作为格式化参数。

2.4 版改变： 参数 indent , width and depth 被添加。

pprint. pprint ( 对象 , stream=None , indent=1 , width=80 , depth=None ) ¶

打印格式化表示 object on stream , followed by a newline. If stream is None , sys.stdout is used. This may be used in the interactive interpreter instead of a print statement for inspecting values. indent , width and depth 会被传递给 PrettyPrinter 构造函数作为格式化参数。

>>> import pprint
>>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
>>> stuff.insert(0, stuff)
>>> pprint.pprint(stuff)
[<Recursion on list with id=...>,
 'spam',
 'eggs',
 'lumberjack',
 'knights',
 'ni']
							

2.4 版改变： 参数 indent , width and depth 被添加。

pprint. isreadable ( 对象 ) ¶

Determine if the formatted representation of object is “readable,” or can be used to reconstruct the value using eval() . This always returns False for recursive objects.

>>> pprint.isreadable(stuff)
False
								

pprint. isrecursive ( 对象 ) ¶

Determine if object requires a recursive representation.

还定义了一个支持函数：

pprint. saferepr ( 对象 ) ¶

返回字符串表示为 object , protected against recursive data structures. If the representation of object exposes a recursive entry, the recursive reference will be represented as <Recursion on typename with id=number> . The representation is not otherwise formatted.

>>> pprint.saferepr(stuff)
"[<Recursion on list with id=...>, 'spam', 'eggs', 'lumberjack', 'knights', 'ni']"
							

8.18.1. PrettyPrinter 对象 ¶

PrettyPrinter 实例具有下列方法：

PrettyPrinter. pformat ( 对象 ) ¶

返回格式化表示 object . This takes into account the options passed to the PrettyPrinter 构造函数。

PrettyPrinter. pprint ( 对象 ) ¶

Print the formatted representation of object on the configured stream, followed by a newline.

The following methods provide the implementations for the corresponding functions of the same names. Using these methods on an instance is slightly more efficient since new PrettyPrinter objects don’t need to be created.

PrettyPrinter. isreadable ( 对象 ) ¶

Determine if the formatted representation of the object is “readable,” or can be used to reconstruct the value using eval() . Note that this returns False for recursive objects. If the depth 参数为 PrettyPrinter is set and the object is deeper than allowed, this returns False .

PrettyPrinter. isrecursive ( 对象 ) ¶

Determine if the object requires a recursive representation.

This method is provided as a hook to allow subclasses to modify the way objects are converted to strings. The default implementation uses the internals of the saferepr() 实现。

PrettyPrinter. format ( 对象 , context , maxlevels , level ) ¶

Returns three values: the formatted version of object as a string, a flag indicating whether the result is readable, and a flag indicating whether recursion was detected. The first argument is the object to be presented. The second is a dictionary which contains the id() of objects that are part of the current presentation context (direct and indirect containers for object that are affecting the presentation) as the keys; if an object needs to be presented which is already represented in context , the third return value should be True . Recursive calls to the format() method should add additional entries for containers to this dictionary. The third argument, maxlevels , gives the requested limit to recursion; this will be 0 if there is no requested limit. This argument should be passed unmodified to recursive calls. The fourth argument, level , gives the current level; recursive calls should be passed a value less than that of the current call.

2.3 版新增。

8.18.2. pprint Example ¶

This example demonstrates several uses of the pprint() function and its parameters.

>>> import pprint
>>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead',
... ('parrot', ('fresh fruit',))))))))
>>> stuff = ['a' * 10, tup, ['a' * 30, 'b' * 30], ['c' * 20, 'd' * 20]]
>>> pprint.pprint(stuff)
['aaaaaaaaaa',
 ('spam',
  ('eggs',
   ('lumberjack',
    ('knights', ('ni', ('dead', ('parrot', ('fresh fruit',)))))))),
 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'],
 ['cccccccccccccccccccc', 'dddddddddddddddddddd']]
>>> pprint.pprint(stuff, depth=3)
['aaaaaaaaaa',
 ('spam', ('eggs', (...))),
 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'],
 ['cccccccccccccccccccc', 'dddddddddddddddddddd']]
>>> pprint.pprint(stuff, width=60)
['aaaaaaaaaa',
 ('spam',
  ('eggs',
   ('lumberjack',
    ('knights',
     ('ni', ('dead', ('parrot', ('fresh fruit',)))))))),
 ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
  'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'],
 ['cccccccccccccccccccc', 'dddddddddddddddddddd']]