115

I do this in Python 2:

"(%d goals, $%d)" % (self.goals, self.penalties)

What is the Python 3 version of this?

I tried searching for examples online but I kept getting Python 2 versions.

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5
  • It was not deprecated; your code works fine. Read more here. Commented Dec 19, 2012 at 4:57
  • 33
    Note for the casual reader: The dollar sign has no special meaning. It is just a dollar sign here. (Thanks Martijn Pieters) Commented Oct 27, 2014 at 15:23
  • 1
    pyformat.info and python-course.eu/python3_formatted_output.php (Not my sites) Commented Jan 13, 2016 at 12:57
  • 1
    The dollar sign made this very confusing.. Commented Jul 19, 2018 at 19:05
  • 1
    Does this answer your question? How do I put a variable inside a string? Commented Dec 8, 2020 at 12:41

5 Answers 5

Reset to default
174

Here are the docs about the "new" format syntax. An example would be:

"({:d} goals, ${:d})".format(self.goals, self.penalties)

If both goals and penalties are integers (i.e. their default format is ok), it could be shortened to:

"({} goals, ${})".format(self.goals, self.penalties)

And since the parameters are fields of self, there's also a way of doing it using a single argument twice (as @Burhan Khalid noted in the comments):

"({0.goals} goals, ${0.penalties})".format(self)

Explaining:

  • {} means just the next positional argument, with default format;
  • {0} means the argument with index 0, with default format;
  • {:d} is the next positional argument, with decimal integer format;
  • {0:d} is the argument with index 0, with decimal integer format.

There are many others things you can do when selecting an argument (using named arguments instead of positional ones, accessing fields, etc) and many format options as well (padding the number, using thousands separators, showing sign or not, etc). Some other examples:

"({goals} goals, ${penalties})".format(goals=2, penalties=4)
"({goals} goals, ${penalties})".format(**self.__dict__)

"first goal: {0.goal_list[0]}".format(self)
"second goal: {.goal_list[1]}".format(self)

"conversion rate: {:.2f}".format(self.goals / self.shots) # '0.20'
"conversion rate: {:.2%}".format(self.goals / self.shots) # '20.45%'
"conversion rate: {:.0%}".format(self.goals / self.shots) # '20%'

"self: {!s}".format(self) # 'Player: Bob'
"self: {!r}".format(self) # '<__main__.Player instance at 0x00BF7260>'

"games: {:>3}".format(player1.games)  # 'games: 123'
"games: {:>3}".format(player2.games)  # 'games:   4'
"games: {:0>3}".format(player2.games) # 'games: 004'

Note: As others pointed out, the new format does not supersede the former, both are available both in Python 3 and the newer versions of Python 2 as well. Some may say it's a matter of preference, but IMHO the newer is much more expressive than the older, and should be used whenever writing new code (unless it's targeting older environments, of course).

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8 Comments

You can also do "({0.goals} goals, ${0.penalties})".format(self)
You need to take the '%' outside of the curly braces, e.g. {:.2f%} -> {:.2f}%
@SuperElectric you mean, in this line: "conversion rate: {:.2%}".format(self.goals / self.shots)? Works fine for me as it is... (Python 3.4) Note that there's no f in it, I'm asking to format as a percentage, not as a floating point number.
You're right; it seems to work in Python 3.4, so that's fine since the OP was asking about Python3. I just found it didn't work with python 2.7.6. "{:.2f}%".format(float_num) works fine for both.
@JohnSchmitt Yes, this example was supposed to give the same exact output as the code given in the question. The $ has no special meaning here, neither in the old format syntax nor in the new, thus should be present in the generated string, unchanged.
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68

Python 3.6 now supports shorthand literal string interpolation with PEP 498. For your use case, the new syntax is simply:

f"({self.goals} goals, ${self.penalties})"

This is similar to the previous .format standard, but lets one easily do things like:

>>> width = 10
>>> precision = 4
>>> value = decimal.Decimal('12.34567')
>>> f'result: {value:{width}.{precision}}'
'result:      12.35'
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12

That line works as-is in Python 3.

>>> sys.version
'3.2 (r32:88445, Oct 20 2012, 14:09:29) \n[GCC 4.5.2]'
>>> "(%d goals, $%d)" % (self.goals, self.penalties)
'(1 goals, $2)'
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2 Comments

OK. COOL. After I posted the question, I was continuing my search and found that we have to do {%d} instead of just %d is that correct, too? Or is the Python2 way the only way to do it?
Python 3 introduces a new syntax - that's the curly braces - but you're not required to use it. You can use either the old or the new. But they are different; if you're using curlies, you don't use percent signs.
2

I like this approach

my_hash = {}
my_hash["goals"] = 3 #to show number
my_hash["penalties"] = "5" #to show string
print("I scored %(goals)d goals and took %(penalties)s penalties" % my_hash)

Note the appended d and s to the brackets respectively.

output will be:

I scored 3 goals and took 5 penalties
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0

"f-strings" can be used since Python 3.6:

f'({self.goals} goals, ${self.penalties})'
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