Question

So I have this code:

    formatter = "%r %r %r %r"

print formatter % (1, 2, 3, 4)
print formatter % ("one", "two", "three", "four")

And I get this output:

1 2 3 4

‘one’ ‘two’ ‘three’ ‘four’

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My question is:

Why does the second line of output have single quotes around it? I’m not quite sure how the %r conversion type really works.

When I change the code to:

formatter = "%r %r %r %r"

print formatter % (1, 2, 3, 4)
print "%s %s %s %s" % ("one", "two", "three", "four")

I get this result:

1 2 3 4

one two three four

I just don’t understand why they work differently. Can someone break it down for me?

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I’ve read:

http://docs.python.org/library/stdtypes.html &

http://docs.python.org/library/functions.html#repr

Answer 1

With the expression 'abc%rdef' % obj , the part '%r' is replaced with repr(obj)

With the expression 'ABC%sDEF' % obj , the part '%s' is replaced with str(obj)

.

repr() is a function that , for common objects, returns a string that is the same as the one you would write in a script to define the object passed as argument to the repr() function:

For many types, this function makes an attempt to return a string that
would yield an object with the same value when passed to eval()
http://docs.python.org/library/functions.html#repr

.

Example 1

if you consider the list defined by li = [12,45,'haze']

print li will print [12,45,’haze’]

print repr(li) will also print [12,45,’haze’] , because [12,45,'haze'] is the sequence of characters that are written in a script to define the list li with this value

Example 2

if you consider the string defined by ss = 'oregon' :

print ss will print oregon , without any quote around

print repr(ss) will print ‘oregon’ , since 'oregon' is the sequence of characters that you must write in a script if you want to define the string ss with the value oregon in a program

.

So, this means that , in fact, for common objects, repr() and str() return strings that are in general equal, except for a string object. That makes repr() particularly interesting for string objects. It is very useful to analyse the contents of HTML codes, for exemple.