How are booleans formatted in Strings in Python?

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Learn more about Teams What do you want the result to be? True and False? You want '%s' then. %b, when it exists, is for binary (as in base-2). – Thomas Wouters Feb 13, 2010 at 22:05 Ho yes! "%s" seems to work just fine. Reply this question and get a lected answer. I used to do "%s" % str(False). Shame on me :) – Juanjo Conti Feb 13, 2010 at 22:07 I always had this distiction in mind, but correct me if I'm wrong. %s (and thus str()) aim to represent the object as transparantly as possible for humans. %r (and thus repr()) aim to represent the object as transparantly as possible for python. For example,


    print(str("foo"))

merely prints

foo

on a new line.


    print(repr("foo"))

however prints


    'foo'

on a new line, including the quotes, since that's what you need to type in the python interpreter to get the corresponding object to the argument in python. – bobismijnnaam Nov 21, 2015 at 13:35

print "{0} {1}".format(True, False);
print "{0:} {1:}".format(True, False);
print "{0:d} {1:d}".format(True, False);
print "{0:f} {1:f}".format(True, False);
print "{0:e} {1:e}".format(True, False);
These are the results
True False
True False
1.000000 0.000000
1.000000e+00 0.000000e+00
Some of the %-format type specifiers (%r, %i) are not available. For details see the Format Specification Mini-Language
                Note that adding formatting options can screw this up. E.g. {:_^5} will get you '__1__' unless you str(...) the booleans.
– Michael
                Apr 24, 2017 at 16:38
                You can get around the problems with type conversions like !s: '{!s:_^5}'.format(True) is 'True_'
– Michael
                Jan 18, 2018 at 17:20
However if you want to actually format the string (e.g. add white space), you encounter Python casting the boolean into the underlying C value (i.e. an int), e.g. 
>>> "{:<8} {}".format(True, False)
'1        False'
To get around this you can cast True as a string, e.g.
>>> "{:<8} {}".format(str(True), False)
'True     False'
To expand on the answer by phd, you can do all that without str()-ing your booleans in the format() call. There are some weird tricks you can exploit to do formatting for booleans with the new style of string interpolation. It also works for f-strings.
The bland, trivial case
'{},{}'.format(True, False)  # 'True,False'
f'{True},{False}'            # 'True,False'
Adding some formatting converts booleans to integers
Any padding length will do this. I am not sure why someone would want it to work this way.
'{:0},{:0}'.format(True, False)  # '1,0'
f'{True:0},{False:0}'            # '1,0'
'{:>5},{:>5}'.format(True, False)  # '    1,    0'
f'{True:>5},{False:>5}'            # '    1,    0'
String coercion can bring back the normal text
Note the !s in there. This is the most direct equivalent to %s. There's also !r for __repr__() and !a for ASCII, but they're not particularly interesting for booleans.
'{!s:>5},{!s:>5}'.format(True, False)  # ' True,False'
f'{True!s:>5},{False!s:>5}'            # ' True,False'
Referring to Python string interpolation
In Python 3.6, string interpolation has been added with a new string literal f prefix
shouldBeTrue = True
print(f"shouldBeTrue={shouldBeTrue}")
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