What is the meaning of %r?

Question

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.

Answer 1

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 

Answer 2

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