关于python中format占位符中的 {!} 参数

在看celery的时候，发现里面有这么一句

print('Request: {0!r}'.format(self.request))

关于里面的{0!r}是什么意思翻了一下文档。

文档里是这么描述的

replacement_field ::=  "{" [field_name] ["!" conversion] [":" format_spec] "}"

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Two conversion flags are currently supported: '!s' which calls str() on the value, and '!r' which calls repr().

Some examples:

"Harold's a clever {0!s}"        # Calls str() on the argument first
"Bring out the holy {name!r}"    # Calls repr() on the argument first

是说感叹号后面跟的是conversion，而conversion有两个值.

分别是s对应str()函数, r对应repr()函数。

因此上面的翻译一下类似于下面

"Harold's a clever {0!s}" == "Harold's a clever str({0})"

"Bring out the holy {name!r}" == "Bring out the holy repr({name})"

实际调用时的写法应该是

"Harold's a clever {0!s}".format(string) == "Harold's a clever {0}".format(str(string))

"Bring out the holy {name!r}".format(string) == "Bring out the holy {name}".format(repr(string))