漂亮的打印命名元组

Question

我从pprint试了pprint，但是它的输出只有一行，没有多行输出，也没有缩进。

Answer 1

我使用namedtuple的_asdict方法。

但是，它返回一个OrderedDict pprint 不会缩进，所以我将它转换为dict：

>>> from collections import namedtuple

>>> Busbar = namedtuple('Busbar', 'id name voltage')
>>> busbar = Busbar(id=102, name='FACTORY', voltage=21.8)

使用pprint 和dict：

>>> from pprint import pprint
>>> pprint(dict(busbar._asdict()))
{'id': 102,
 'name': 'FACTORY',
 'voltage': 21.8}

Answer 2

Python 3 中的 pprint PrettyPrinter 比 Python 2 中的可扩展性强得多。您可以创建自己的打印机，如下所示，为要处理的对象添加方法，而不会过多地使用 pprint“私有”方法和属性。

您可以在此处查看在线示例：https://repl.it/HkDd/1

from io import StringIO
import pprint

class MyPrettyPrinter(pprint.PrettyPrinter):
    def format_namedtuple(self, object, stream, indent, allowance, context, level):
        # Code almost equal to _format_dict, see pprint code
        write = stream.write
        write(object.__class__.__name__ + '(')
        object_dict = object._asdict()
        length = len(object_dict)
        if length:
            # We first try to print inline, and if it is too large then we print it on multiple lines
            inline_stream = StringIO()
            self.format_namedtuple_items(object_dict.items(), inline_stream, indent, allowance + 1, context, level, inline=True)
            max_width = self._width - indent - allowance
            if len(inline_stream.getvalue()) > max_width:
                self.format_namedtuple_items(object_dict.items(), stream, indent, allowance + 1, context, level, inline=False)
            else:
                stream.write(inline_stream.getvalue())
        write(')')

    def format_namedtuple_items(self, items, stream, indent, allowance, context, level, inline=False):
        # Code almost equal to _format_dict_items, see pprint code
        indent += self._indent_per_level
        write = stream.write
        last_index = len(items) - 1
        if inline:
            delimnl = ', '
        else:
            delimnl = ',\n' + ' ' * indent
            write('\n' + ' ' * indent)
        for i, (key, ent) in enumerate(items):
            last = i == last_index
            write(key + '=')
            self._format(ent, stream, indent + len(key) + 2,
                         allowance if last else 1,
                         context, level)
            if not last:
                write(delimnl)

    def _format(self, object, stream, indent, allowance, context, level):
        # We dynamically add the types of our namedtuple and namedtuple like 
        # classes to the _dispatch object of pprint that maps classes to
        # formatting methods
        # We use a simple criteria (_asdict method) that allows us to use the
        # same formatting on other classes but a more precise one is possible
        if hasattr(object, '_asdict') and type(object).__repr__ not in self._dispatch:
            self._dispatch[type(object).__repr__] = MyPrettyPrinter.format_namedtuple
        super()._format(object, stream, indent, allowance, context, level)

并像这样使用它：

from collections import namedtuple

Segment = namedtuple('Segment', 'p1 p2')
# Your own namedtuple-like class
class Node:
    def __init__(self, x, y, segments=[]):
        self.x = x
        self.y = y
        self.segments = segments

    def _asdict(self):
        return {"x": self.x, "y": self.y, "segments": self.segments}

    # Default repr
    def __repr__(self):
        return "Node(x={}, y={}, segments={})".format(self.x, self.y, self.segments)

# A circular structure for the demo
node = Node(0, 0)
segments = [
    Segment(node, Node(1, 1)),
    Segment(node, Node(2, 1)),
    Segment(node, Node(1, 2, segments=[
      Segment(Node(2, 3), Node(1, 1)),
    ])),
]
node.segments = segments

pp = MyPrettyPrinter(indent=2, depth=2)
pp.pprint(node)

输出

Node(
  x=0,
  y=0,
  segments=[ Segment(
                p1=<Recursion on Node with id=139778851454536>,
                p2=Node(x=1, y=1, segments=[])),
              Segment(
                p1=<Recursion on Node with id=139778851454536>,
                p2=Node(x=2, y=1, segments=[])),
              Segment(
                p1=<Recursion on Node with id=139778851454536>,
                p2=Node(x=1, y=2, segments=[...]))])

Answer 3

与此处的所有其他解决方案不同，此解决方案是通用的，也适用于其他容器中的命名元组：

import black

# value_to_print can either be a namedtuple, or a container containing tuples,
# or a namedtuple containing containers containing other namedtuples,
# or whatever else you want.
print(black.format_str(repr(value_to_print), mode=black.Mode()))

这需要安装黑色，可以通过pip install black完成。