何时在 Python 中使用 %r 而不是 %s? [英] When to use %r instead of %s in Python?
问题描述
在 Learn Python the Hard Way 第 21 页上,我看到了以下代码示例:
x = "有 %d 种人."% 10...打印我说:%r."% X
为什么在这里使用 %r
而不是 %s
?什么时候用%r
,什么时候用%s
?
%s
说明符使用 str()
和 %r
使用 repr()
.
对于某些对象(例如整数),它们产生相同的结果,但是 repr()
的特殊之处在于(对于可能的类型)它通常返回一个有效的 Python 语法的结果,可用于明确地重新创建它所代表的对象.
这是一个使用日期的示例:
<预><代码>>>>导入日期时间>>>d = datetime.date.today()>>>字符串(d)'2011-05-14'>>>代表(d)'datetime.date(2011, 5, 14)'repr()
不生成的类型Python 语法包括那些指向外部资源的语法,例如 file
,您不能保证在不同的上下文中重新创建.
On Learn Python the Hard Way page 21, I see this code example:
x = "There are %d types of people." % 10
...
print "I said: %r." % x
Why is %r
used here instead of %s
? When would you use %r
, and when would you use %s
?
The %s
specifier converts the object using str()
, and %r
converts it using repr()
.
For some objects such as integers, they yield the same result, but repr()
is special in that (for types where this is possible) it conventionally returns a result that is valid Python syntax, which could be used to unambiguously recreate the object it represents.
Here's an example, using a date:
>>> import datetime
>>> d = datetime.date.today()
>>> str(d)
'2011-05-14'
>>> repr(d)
'datetime.date(2011, 5, 14)'
Types for which repr()
doesn't produce Python syntax include those that point to external resources such as a file
, which you can't guarantee to recreate in a different context.
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