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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'

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?

I've read:

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

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

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  • This is a good question, particularly if you are a beginner. Then I upvoted Commented Aug 28, 2011 at 23:36

2 Answers 2

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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.

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7 Comments

Ooooo! And the lightbulb goes on. This is much appreciated.
Do you have an examples of how it's "useful to analyse the contents of HTML codes."
@Dorje Yes. Read first this post: (stackoverflow.com/questions/7213970/…) In the second part of the post, there is this instruction li = htmlcode.splitlines(True) followed by this other useful instruction print '\n'.join(str(i) + ' ' + repr(line)+'\n' for i,line in enumerate(li) if 275<i<300) that displays a very useful representation of a portion of the content of an HTML code. Delete the portion if 275<i<300 and you obtain a rpresentation of the whole content of the HTML fetched code.
@Dorje More complex and more in relation to your question is this post (stackoverflow.com/questions/7206143/python-regex-problem/…)
@Dorje By the way, re-reading the docs concerning repr(), it reminded me that we can write print `x` instead of repr(x)
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%s tell's python to call the str() function on each element of your tuple. %r tell's python to call the repr() function on each element of your tuple.

By the docs:

str():

Return a string containing a nicely printable representation of an object. For strings, this returns the string itself.

repr():

Return a string containing a printable representation of an object.

This means, if the object you call repr() on is a string object (in python everything is an object) it shows you how the different characters are represented.

@your specific question: I assume that the "..." indicate, that it is a string. If you call repr() on an int there are no "...".

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Thanks for the explanation. This really helped explain the docs more. "This means, if the object you call repr() on is a string object (in python everything is an object) it shows you how the different characters are represented."

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