What is the meaning of %r?

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

It calls repr() on the object and inserts the resulting string.

It prints the replacement as a string with repr().