pprint
— 数据美化打印机
¶
源代码： Lib/pprint.py
pprint
模块提供可以用作解释器输入形式的 pretty-print (美化打印) 任意 Python 数据结构的能力。若格式化的结构包括非基础 Python 类型的对象，表示可能无法被加载。若是包括文件、套接字或类的对象及许多无法表示成 Python 文字的其它对象，可能属于此情况。
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。
字典按键排序在计算显示之前。
pprint
模块定义 1 个类：
pprint.
PrettyPrinter
(
indent=1
,
width=80
,
depth=None
,
stream=None
,
*
,
compact=False
)
¶
构造
PrettyPrinter
instance. This constructor understands several keyword parameters. An output stream may be set using the
stream
keyword; the only method used on the stream object is the file protocol’s
write()
method. If not specified, the
PrettyPrinter
adopts
sys.stdout
. The amount of indentation added for each recursive level is specified by
indent
; the default is one. Other values can cause output to look a little odd, but can make nesting easier to spot. The number of levels which may be printed is controlled by
depth
; if the data structure being printed is too deep, the next contained level is replaced by
...
. By default, there is no constraint on the depth of the objects being formatted. The desired output width is constrained using the
width
parameter; the default is 80 characters. If a structure cannot be formatted within the constrained width, a best effort will be made. If
compact
is false (the default) each item of a long sequence will be formatted on a separate line. If
compact
is true, as many items as will fit within the
width
will be formatted on each output line.
3.4 版改变： 添加 compact 参数。
>>> 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']
>>> pp = pprint.PrettyPrinter(width=41, compact=True)
>>> 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', (...)))))))
pprint
模块还提供几个快捷函数：
pprint.
pformat
(
object
,
indent=1
,
width=80
,
depth=None
,
*
,
compact=False
)
¶
Return the formatted representation of
object
as a string.
indent
,
width
,
depth
and
compact
will be passed to the
PrettyPrinter
constructor as formatting parameters.
3.4 版改变： 添加 compact 参数。
pprint.
pprint
(
object
,
stream=None
,
indent=1
,
width=80
,
depth=None
,
*
,
compact=False
)
¶
Prints the formatted representation of
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 the
print()
function for inspecting values (you can even reassign
print
=
pprint.pprint
for use within a scope).
indent
,
width
,
depth
and
compact
will be passed to the
PrettyPrinter
constructor as formatting parameters.
3.4 版改变： 添加 compact 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']
pprint.
isreadable
(
object
)
¶
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
(
object
)
¶
Determine if object requires a recursive representation.
One more support function is also defined:
pprint.
saferepr
(
object
)
¶
Return a string representation of
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']"
PrettyPrinter
实例具有下列方法：
PrettyPrinter.
pformat
(
object
)
¶
Return the formatted representation of
object
. This takes into account the options passed to the
PrettyPrinter
构造函数。
PrettyPrinter.
pprint
(
object
)
¶
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
(
object
)
¶
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
parameter of the
PrettyPrinter
is set and the object is deeper than allowed, this returns
False
.
PrettyPrinter.
isrecursive
(
object
)
¶
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
(
object
,
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.
To demonstrate several uses of the
pprint()
function and its parameters, let’s fetch information about a project from
PyPI
:
>>> import json
>>> import pprint
>>> from urllib.request import urlopen
>>> with urlopen('https://pypi.org/pypi/sampleproject/json') as resp:
... project_info = json.load(resp)['info']
In its basic form,
pprint()
shows the whole object:
>>> pprint.pprint(project_info)
{'author': 'The Python Packaging Authority',
'author_email': 'pypa-dev@googlegroups.com',
'bugtrack_url': None,
'classifiers': ['Development Status :: 3 - Alpha',
'Intended Audience :: Developers',
'License :: OSI Approved :: MIT License',
'Programming Language :: Python :: 2',
'Programming Language :: Python :: 2.6',
'Programming Language :: Python :: 2.7',
'Programming Language :: Python :: 3',
'Programming Language :: Python :: 3.2',
'Programming Language :: Python :: 3.3',
'Programming Language :: Python :: 3.4',
'Topic :: Software Development :: Build Tools'],
'description': 'A sample Python project\n'
'=======================\n'
'\n'
'This is the description file for the project.\n'
'\n'
'The file should use UTF-8 encoding and be written using '
'ReStructured Text. It\n'
'will be used to generate the project webpage on PyPI, and '
'should be written for\n'
'that purpose.\n'
'\n'
'Typical contents for this file would include an overview of '
'the project, basic\n'
'usage examples, etc. Generally, including the project '
'changelog in here is not\n'
'a good idea, although a simple "What\'s New" section for the '
'most recent version\n'
'may be appropriate.',
'description_content_type': None,
'docs_url': None,
'download_url': 'UNKNOWN',
'downloads': {'last_day': -1, 'last_month': -1, 'last_week': -1},
'home_page': 'https://github.com/pypa/sampleproject',
'keywords': 'sample setuptools development',
'license': 'MIT',
'maintainer': None,
'maintainer_email': None,
'name': 'sampleproject',
'package_url': 'https://pypi.org/project/sampleproject/',
'platform': 'UNKNOWN',
'project_url': 'https://pypi.org/project/sampleproject/',
'project_urls': {'Download': 'UNKNOWN',
'Homepage': 'https://github.com/pypa/sampleproject'},
'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
'requires_dist': None,
'requires_python': None,
'summary': 'A sample Python project',
'version': '1.2.0'}
The result can be limited to a certain depth (ellipsis is used for deeper contents):
>>> pprint.pprint(project_info, depth=1)
{'author': 'The Python Packaging Authority',
'author_email': 'pypa-dev@googlegroups.com',
'bugtrack_url': None,
'classifiers': [...],
'description': 'A sample Python project\n'
'=======================\n'
'\n'
'This is the description file for the project.\n'
'\n'
'The file should use UTF-8 encoding and be written using '
'ReStructured Text. It\n'
'will be used to generate the project webpage on PyPI, and '
'should be written for\n'
'that purpose.\n'
'\n'
'Typical contents for this file would include an overview of '
'the project, basic\n'
'usage examples, etc. Generally, including the project '
'changelog in here is not\n'
'a good idea, although a simple "What\'s New" section for the '
'most recent version\n'
'may be appropriate.',
'description_content_type': None,
'docs_url': None,
'download_url': 'UNKNOWN',
'downloads': {...},
'home_page': 'https://github.com/pypa/sampleproject',
'keywords': 'sample setuptools development',
'license': 'MIT',
'maintainer': None,
'maintainer_email': None,
'name': 'sampleproject',
'package_url': 'https://pypi.org/project/sampleproject/',
'platform': 'UNKNOWN',
'project_url': 'https://pypi.org/project/sampleproject/',
'project_urls': {...},
'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
'requires_dist': None,
'requires_python': None,
'summary': 'A sample Python project',
'version': '1.2.0'}
Additionally, maximum character width can be suggested. If a long object cannot be split, the specified width will be exceeded:
>>> pprint.pprint(project_info, depth=1, width=60)
{'author': 'The Python Packaging Authority',
'author_email': 'pypa-dev@googlegroups.com',
'bugtrack_url': None,
'classifiers': [...],
'description': 'A sample Python project\n'
'=======================\n'
'\n'
'This is the description file for the '
'project.\n'
'\n'
'The file should use UTF-8 encoding and be '
'written using ReStructured Text. It\n'
'will be used to generate the project '
'webpage on PyPI, and should be written '
'for\n'
'that purpose.\n'
'\n'
'Typical contents for this file would '
'include an overview of the project, '
'basic\n'
'usage examples, etc. Generally, including '
'the project changelog in here is not\n'
'a good idea, although a simple "What\'s '
'New" section for the most recent version\n'
'may be appropriate.',
'description_content_type': None,
'docs_url': None,
'download_url': 'UNKNOWN',
'downloads': {...},
'home_page': 'https://github.com/pypa/sampleproject',
'keywords': 'sample setuptools development',
'license': 'MIT',
'maintainer': None,
'maintainer_email': None,
'name': 'sampleproject',
'package_url': 'https://pypi.org/project/sampleproject/',
'platform': 'UNKNOWN',
'project_url': 'https://pypi.org/project/sampleproject/',
'project_urls': {...},
'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
'requires_dist': None,
'requires_python': None,
'summary': 'A sample Python project',
'version': '1.2.0'}