%r 是什么意思?

问题描述

下面语句中%r是什么意思?

print '%r' % (1)

我想我听说过 %s、%d 和 %f 但从未听说过这个.

解决方案

背景:

在 Python 中，有两个内置函数可以将对象转换为字符串:str 与 代表.str 应该是一个友好的、人类可读的字符串.repr 应该包含有关对象内容的详细信息(有时，它们会返回相同的内容，例如对于整数).按照惯例，如果有一个 Python 表达式将评估为另一个 == 对象，repr 将返回这样的表达式，例如

>>> 打印 repr('hi')'hi' # 注意这里的引号而不是...>>> 打印 str('hi')你好

如果返回一个表达式对一个对象没有意义，repr 应该返回一个由 < 包围的字符串.和 > 符号，例如.

回答您最初的问题:

%s <-> str
%r <-> repr

另外:

您可以通过实现 __str__ 和 __repr__ 方法.

 Foo 类:def __init__(self, foo):self.foo = foodef __eq__(自我，其他):"""实现 ==."""返回 self.foo == other.foodef __repr__(self):# 如果你评估这个函数的返回值，# 你会得到另一个 Foo 实例，它是 == 到 self返回 "Foo(%r)" % self.foo

What's the meaning of %r in the following statement?

print '%r' % (1)

I think I've heard of %s, %d, and %f but never heard of this.

解决方案

Background:

In Python, there are two builtin functions for turning an object into a string: str vs. repr. str is supposed to be a friendly, human readable string. repr is supposed to include detailed information about an object's contents (sometimes, they'll return the same thing, such as for integers). By convention, if there's a Python expression that will eval to another object that's ==, repr will return such an expression e.g.

>>> print repr('hi')
'hi'  # notice the quotes here as opposed to...
>>> print str('hi')
hi

If returning an expression doesn't make sense for an object, repr should return a string that's surrounded by < and > symbols e.g. <blah>.

To answer your original question:

%s <-> str
%r <-> repr

In addition:

You can control the way an instance of your own classes convert to strings by implementing __str__ and __repr__ methods.

class Foo:

  def __init__(self, foo):
    self.foo = foo

  def __eq__(self, other):
    """Implements ==."""
    return self.foo == other.foo

  def __repr__(self):
    # if you eval the return value of this function,
    # you'll get another Foo instance that's == to self
    return "Foo(%r)" % self.foo

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