如何使用python-3.x中的字典格式化字符串?

I am a big fan of using dictionaries to format strings. It helps me read the string format I am using as well as let me take advantage of existing dictionaries. For example:

我非常喜欢使用字典来格式化字符串。它帮助我读取我使用的字符串格式，并让我利用现有的字典。例如:

class MyClass:
    def __init__(self):
        self.title = 'Title'

a = MyClass()
print 'The title is %(title)s' % a.__dict__

path = '/path/to/a/file'
print 'You put your file here: %(path)s' % locals()

However I cannot figure out the python 3.x syntax for doing the same (or if that is even possible). I would like to do the following

但是我不能算出python 3。执行相同的语法(如果可能的话)。我想做以下的事情。

# Fails, KeyError 'latitude'
geopoint = {'latitude':41.123,'longitude':71.091}
print '{latitude} {longitude}'.format(geopoint)

# Succeeds
print '{latitude} {longitude}'.format(latitude=41.123,longitude=71.091)

6 个解决方案

#1

256

Is this good for you?

这对你有好处吗?

geopoint = {'latitude':41.123,'longitude':71.091}
print('{latitude} {longitude}'.format(**geopoint))

#2

To unpack a dictionary into keyword arguments, use **. Also,, new-style formatting supports referring to attributes of objects and items of mappings:

要将词典解压到关键字参数中，请使用**。另外，新样式的格式支持引用对象的属性和映射的项:

'{0[latitude]} {0[longitude]}'.format(geopoint)
'The title is {0.title}s'.format(a) # the a from your first example

#3

As Python 3.0 and 3.1 are EOL'ed and no one uses them, you can and should use str.format_map(mapping) (Python 3.2+):

由于Python 3.0和3.1都是EOL，而且没有人使用它们，所以您可以并且应该使用str.format_map(映射)(Python 3.2+):

Similar to str.format(**mapping), except that mapping is used directly and not copied to a dict. This is useful if for example mapping is a dict subclass.

类似于str.format(**映射)，除非该映射是直接使用的，而不是复制到命令中。

What this means is that you can use for example a defaultdict that would supply a default value for keys that are missing:

这意味着您可以使用一个defaultdict，它将为丢失的键提供默认值:

>>> from collections import defaultdict
>>> vals = defaultdict(lambda: '<unset>', {'bar': 'baz'})
>>> 'foo is {foo} and bar is {bar}'.format_map(vals)
'foo is <unset> and bar is baz'

Even if the mapping provided is a dict, not a subclass, this would probably still be slightly faster.

即使提供的映射是命令，而不是子类，这可能仍然会稍微快一点。

The difference is not big though, given

但差别并不大。

>>> d = dict(foo='x', bar='y', baz='z')

then

然后

>>> 'foo is {foo}, bar is {bar} and baz is {baz}'.format_map(d)

is about 10 ns (2 %) faster than

大约有10个ns(2%)比?

>>> 'foo is {foo}, bar is {bar} and baz is {baz}'.format(**d)

on my Python 3.4.3. The difference would probably be larger as more keys are in the dictionary, and

在我的Python 3.4.3。如果字典中有更多的键，那么差异可能会更大。

Note that the format language is much more flexible than that though; they can contain indexed expressions, attribute accesses and so on, so you can format a whole object, or 2 of them:

请注意，格式语言要比这个灵活得多;它们可以包含索引表达式、属性访问等，因此可以格式化整个对象，或者其中2个:

>>> p1 = {'latitude':41.123,'longitude':71.091}
>>> p2 = {'latitude':56.456,'longitude':23.456}
>>> '{0[latitude]} {0[longitude]} - {1[latitude]} {1[longitude]}'.format(p1, p2)
'41.123 71.091 - 56.456 23.456'

Starting from 3.6 you can use the interpolated strings too:

从3.6开始，你也可以使用插值字符串:

>>> f'lat:{p1["latitude"]} lng:{p1["longitude"]}'
'lat:41.123 lng:71.091'

You just need to remember to use the other quote characters within the nested quotes. Another upside of this approach is that it is much faster than calling a formatting method.

您只需要记住在嵌套引号内使用其他引用字符。这种方法的另一个优点是，它比调用格式化方法快得多。

#4

print("{latitude} {longitude}".format(**geopoint))

#5

The Python 2 syntax works in Python 3 as well:

Python 2的语法也适用于Python 3:

>>> class MyClass:
...     def __init__(self):
...         self.title = 'Title'
... 
>>> a = MyClass()
>>> print('The title is %(title)s' % a.__dict__)
The title is Title
>>> 
>>> path = '/path/to/a/file'
>>> print('You put your file here: %(path)s' % locals())
You put your file here: /path/to/a/file

#6

Since the question is specific to Python 3, here's using the new f-string syntax:

由于这个问题是针对Python 3的，这里使用了新的f-string语法:

>>> geopoint = {'latitude':41.123,'longitude':71.091}
>>> print(f'{geopoint["latitude"]} {geopoint["longitude"]}')
41.123 71.091

Note the outer single quotes and inner double quotes (you could also do it the other way around).

注意外部单引号和内双引号(您也可以反过来)。

#1

256