Python way of printing: with 'format' or percent form?

Question

In Python there seem to be two different ways of generating formatted output:

user = "Alex"
number = 38746
print("%s asked %d questions on stackoverflow.com" % (user, number))
print("{0} asked {1} questions on stackoverflow.com".format(user, number))

Is there one way to be preferred over the other? Are they equivalent, what is the difference? What form should be used, especially for Python3?

score 108 · Accepted Answer · edited May 09 '19 at 03:49

108

Use the format method, especially if you're concerned about Python 3 and the future. From the documentation:

The formatting operations described here are modelled on C's printf() syntax. They only support formatting of certain builtin types. The use of a binary operator means that care may be needed in order to format tuples and dictionaries correctly. As the new :ref:string-formatting syntax is more flexible and handles tuples and dictionaries naturally, it is recommended for new code. However, there are no current plans to deprecate printf-style formatting.

edited May 09 '19 at 03:49

Chandan Kumar

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answered Sep 12 '12 at 07:00

BrenBarn

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New documentation says this about the percent operator: "The formatting operations described here exhibit a variety of quirks that lead to a number of common errors ..." but it is **not** deprecated. http://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting – guettli Sep 03 '13 at 15:14
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It's not officially deprecated, but you're encouraged not to use it. – BrenBarn Sep 03 '13 at 16:18
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Related: http://bugs.python.org/issue14123 – guettli Sep 11 '13 at 07:35
Is .format significantly slower than % ? – Qi Fan Mar 03 '16 at 22:22
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From Python 3.6, you can [use f-strings to access previously defined variables](https://docs.python.org/3/whatsnew/3.6.html#whatsnew36-pep498): `print(f"{user} asked {number} questions on stackoverflow.com"` – joelostblom May 26 '17 at 15:44

score 25 · Answer 2 · answered Sep 12 '12 at 07:05

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.format was introduced in Python2.6

If you need backward compatibility with earlier Python, you should use %

For Python3 and newer you should use .format for sure

.format is more powerful than %. Porting % to .format is easy but the other way round can be non trivial

answered Sep 12 '12 at 07:05

John La Rooy

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how is it more powerful ? – yossi Dec 07 '14 at 12:35
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@yossi Here's one example http://stackoverflow.com/a/3228928/174728. It also lets you do key/index lookups `import sys;"{[version]}".format(vars(sys))` – John La Rooy Dec 07 '14 at 22:24
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how about: `import sys;"%(version)s" % (vars(sys))` – Pax0r Jan 19 '16 at 16:10
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@Pax0r: The linked example is `'{num:{fill}{width}}'.format(num=123, fill='0', width=6)`. You can't do this with `%` unless you "double escape" and apply it twice – John La Rooy Jan 19 '16 at 23:58
'%s' % (str(123).rjust(6, '0')) – Sean Bradley Mar 01 '19 at 16:07
@Sean, that's formatting a string, not a number. If I just manipulate a value into a string someway there is not need for an extra layer of formatting at all. Indeed `'%s'%` adds nothing extra to the string you already created. – John La Rooy Mar 02 '19 at 21:44
https://ideone.com/FsIZFy – Sean Bradley Mar 03 '19 at 12:03

score 8 · Answer 3 · answered Sep 12 '12 at 07:04

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The docs say that the format method is preferred for new code. There are currently no plans to remove % formatting, though.

answered Sep 12 '12 at 07:04

riamse

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score 8 · Answer 4 · answered Dec 23 '13 at 07:46

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You can use both .No one said % formatting expression is deprecated.However,as stated before the format method call is a tad more powerful. Also note that the % expressions are bit more concise and easier to code.Try them and see what suits you best

answered Dec 23 '13 at 07:46

devsaw

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It's probably worth noting that `logging` module uses `%`-like syntax, so it may be preferred for consistency reasons. – sshilovsky Sep 14 '15 at 12:35

Python way of printing: with 'format' or percent form?

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