python - %r 是什么意思？

Question

下面语句中的%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。

Answer 1

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 repr . 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，例如整数)。按照惯例，如果有一个 Python 表达式将评估另一个对象 ==，repr 将返回这样的表达式，例如

>>> 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