问题:在Python中使用多个参数进行字符串格式化(例如’%s…%s’)

我有一个看起来像的字符串,'%s in %s'并且我想知道如何分隔参数,以便它们是两个不同的%s。我来自Java的想法是这样的:

'%s in %s' % unicode(self.author),  unicode(self.publication)

但这不起作用,因此它在Python中的外观如何?

I have a string that looks like '%s in %s' and I want to know how to seperate the arguments so that they are two different %s. My mind coming from Java came up with this:

'%s in %s' % unicode(self.author),  unicode(self.publication)

But this doesn’t work so how does it look in Python?


回答 0

马克·西达德(Mark Cidade)的答案是正确的-您需要提供一个元组。

但是从Python 2.6起,您可以使用代替%

'{0} in {1}'.format(unicode(self.author,'utf-8'),  unicode(self.publication,'utf-8'))

%不再鼓励使用for格式化字符串。

这种字符串格式设置方法是Python 3.0中的新标准,应优先于新代码中“字符串格式设置操作”中描述的%格式设置。

Mark Cidade’s answer is right – you need to supply a tuple.

However from Python 2.6 onwards you can use instead of %:

'{0} in {1}'.format(unicode(self.author,'utf-8'),  unicode(self.publication,'utf-8'))

Usage of % for formatting strings is no longer encouraged.

This method of string formatting is the new standard in Python 3.0, and should be preferred to the % formatting described in String Formatting Operations in new code.


回答 1

如果使用多个参数,则必须将其放在一个元组中(请注意额外的括号):

'%s in %s' % (unicode(self.author),  unicode(self.publication))

正如EOL所指出的那样,该unicode()函数通常假定默认为ascii编码,因此,如果您使用非ASCII字符,则显式传递编码会更安全:

'%s in %s' % (unicode(self.author,'utf-8'),  unicode(self.publication('utf-8')))

从Python 3.0开始,最好改用以下str.format()语法:

'{0} in {1}'.format(unicode(self.author,'utf-8'),unicode(self.publication,'utf-8'))

If you’re using more than one argument it has to be in a tuple (note the extra parentheses):

'%s in %s' % (unicode(self.author),  unicode(self.publication))

As EOL points out, the unicode() function usually assumes ascii encoding as a default, so if you have non-ASCII characters, it’s safer to explicitly pass the encoding:

'%s in %s' % (unicode(self.author,'utf-8'),  unicode(self.publication('utf-8')))

And as of Python 3.0, it’s preferred to use the str.format() syntax instead:

'{0} in {1}'.format(unicode(self.author,'utf-8'),unicode(self.publication,'utf-8'))

回答 2

在元组/映射对象上有多个参数 format

以下是文档摘录:

给定的format % values中的%转换规范format将替换为的零个或多个元素values。效果类似于使用sprintf() C语言中的用法。

如果format需要单个参数,则值可以是单个非元组对象。否则,值必须是一个具有由formatstring 指定的项目数的元组或者是一个映射对象(例如,字典)。

参考资料


开启str.format而不是%

%操作员的新替代方法是使用str.format。以下是文档摘录:

str.format(*args, **kwargs)

执行字符串格式化操作。调用此方法的字符串可以包含文字文本或用大括号分隔的替换字段{}。每个替换字段都包含位置参数的数字索引或关键字参数的名称。返回字符串的副本,其中每个替换字段都用相应参数的字符串值替换。

此方法是Python 3.0中的新标准,应优先于%formatting

参考资料


例子

以下是一些用法示例:

>>> '%s for %s' % ("tit", "tat")
tit for tat

>>> '{} and {}'.format("chicken", "waffles")
chicken and waffles

>>> '%(last)s, %(first)s %(last)s' % {'first': "James", 'last': "Bond"}
Bond, James Bond

>>> '{last}, {first} {last}'.format(first="James", last="Bond")
Bond, James Bond

也可以看看

On a tuple/mapping object for multiple argument format

The following is excerpt from the documentation:

Given format % values, % conversion specifications in format are replaced with zero or more elements of values. The effect is similar to the using sprintf() in the C language.

If format requires a single argument, values may be a single non-tuple object. Otherwise, values must be a tuple with exactly the number of items specified by the format string, or a single mapping object (for example, a dictionary).

References


On str.format instead of %

A newer alternative to % operator is to use str.format. Here’s an excerpt from the documentation:

str.format(*args, **kwargs)

Perform a string formatting operation. The string on which this method is called can contain literal text or replacement fields delimited by braces {}. Each replacement field contains either the numeric index of a positional argument, or the name of a keyword argument. Returns a copy of the string where each replacement field is replaced with the string value of the corresponding argument.

This method is the new standard in Python 3.0, and should be preferred to % formatting.

References


Examples

Here are some usage examples:

>>> '%s for %s' % ("tit", "tat")
tit for tat

>>> '{} and {}'.format("chicken", "waffles")
chicken and waffles

>>> '%(last)s, %(first)s %(last)s' % {'first': "James", 'last': "Bond"}
Bond, James Bond

>>> '{last}, {first} {last}'.format(first="James", last="Bond")
Bond, James Bond

See also


回答 3

您必须将值放在括号中:

'%s in %s' % (unicode(self.author),  unicode(self.publication))

在这里,第一个%sunicode(self.author)将被放置。第二%sunicode(self.publication)将使用。

注意:你应该有利于string formatting%符号。更多信息在这里

You must just put the values into parentheses:

'%s in %s' % (unicode(self.author),  unicode(self.publication))

Here, for the first %s the unicode(self.author) will be placed. And for the second %s, the unicode(self.publication) will be used.

Note: You should favor string formatting over the % Notation. More info here


回答 4

到目前为止,发布的一些答案存在一个严重的问题:unicode()从默认编码(通常为ASCII)解码;实际上,unicode()试图通过将给定的字节转换为字符来“感知”。因此,以下代码(基本上是前面的答案所建议的)在我的计算机上失败:

# -*- coding: utf-8 -*-
author = 'éric'
print '{0}'.format(unicode(author))

给出:

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    print '{0}'.format(unicode(author))
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 0: ordinal not in range(128)

失败的原因是author不只包含ASCII字节(即[0; 127]中的值),并且unicode()默认情况下(在许多计算机上)从ASCII解码。

一个可靠的解决方案是显式提供您的字段中使用的编码。以UTF-8为例:

u'{0} in {1}'.format(unicode(self.author, 'utf-8'), unicode(self.publication, 'utf-8'))

(或不使用initial u,这取决于您要使用Unicode结果还是字节字符串)。

在这一点上,可能要考虑让authorand publication字段为Unicode字符串,而不是在格式化期间对其进行解码。

There is a significant problem with some of the answers posted so far: unicode() decodes from the default encoding, which is often ASCII; in fact, unicode() tries to make “sense” of the bytes it is given by converting them into characters. Thus, the following code, which is essentially what is recommended by previous answers, fails on my machine:

# -*- coding: utf-8 -*-
author = 'éric'
print '{0}'.format(unicode(author))

gives:

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    print '{0}'.format(unicode(author))
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 0: ordinal not in range(128)

The failure comes from the fact that author does not contain only ASCII bytes (i.e. with values in [0; 127]), and unicode() decodes from ASCII by default (on many machines).

A robust solution is to explicitly give the encoding used in your fields; taking UTF-8 as an example:

u'{0} in {1}'.format(unicode(self.author, 'utf-8'), unicode(self.publication, 'utf-8'))

(or without the initial u, depending on whether you want a Unicode result or a byte string).

At this point, one might want to consider having the author and publication fields be Unicode strings, instead of decoding them during formatting.


回答 5

对于python2,您也可以执行此操作

'%(author)s in %(publication)s'%{'author':unicode(self.author),
                                  'publication':unicode(self.publication)}

如果您有很多可替代的论点(特别是在进行国际化的情况下),这将很方便

Python2.6及更高版本支持 .format()

'{author} in {publication}'.format(author=self.author,
                                   publication=self.publication)

For python2 you can also do this

'%(author)s in %(publication)s'%{'author':unicode(self.author),
                                  'publication':unicode(self.publication)}

which is handy if you have a lot of arguments to substitute (particularly if you are doing internationalisation)

Python2.6 onwards supports .format()

'{author} in {publication}'.format(author=self.author,
                                   publication=self.publication)

回答 6

您还可以通过以下方式干净,简单地使用它(但是错误!因为您应该format像Mark Byers所说的那样使用):

print 'This is my %s formatted with %d arguments' % ('string', 2)

You could also use it clean and simple (but wrong! because you should use format like Mark Byers said) by doing:

print 'This is my %s formatted with %d arguments' % ('string', 2)

回答 7

为了完整起见,在PEP-498中引入了Python 3.6 f-string 。这些字符串可以

使用最小语法将表达式嵌入字符串文字中。

这意味着对于您的示例,您还可以使用:

f'{self.author} in {self.publication}'

For completeness, in python 3.6 f-string are introduced in PEP-498. These strings make it possible to

embed expressions inside string literals, using a minimal syntax.

That would mean that for your example you could also use:

f'{self.author} in {self.publication}'

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