In python you can specify the format inside the curved brackets.

You can do things such as

>>> '{:b}'.format(2)
'10'

In your case, d prints as decimal integer.

You can find all the doc here

https://docs.python.org/2/library/string.html#format-specification-mini-language

The "%" operator is used to format a set of variables enclosed in a tuple (a fixed size list), together with a format string.

print ("%d squared is %d" % (10, 10*10))

The % operators in the string are replaced in order by the elements in the tuple.

%d is used for integers, where as %s is used for strings

Eg.

>>>name = "John"
>>>age = 23
>>>print "%s is %d years old." % (name, age)
John is 23 years old.

I'm one of those who prefers words to punctuation -- it's one of the reasons I've picked Python over Perl, for example. "Life is better without braces" (an old Python motto which went on a T-shirt with a cartoon of a smiling teenager;-), after all (originally intended to refer to braces vs indentation for grouping, of course, but, hey, braces are braces!-).

"Paying" some nanoseconds (for the purpose of using a clear, readable short word instead of braces, brackets and whatnots) is generally affordable (it's mostly the cost of lookups into the built-ins' namespace, a price you pay every time you use a built-in type or function, and you can mildly optimize it back by hoisting some lookups out of loops).

So, I'm generally the one who likes to write dict() for {}, list(L) in lieu of L[:] as well as list() for [], tuple() for (), and so on -- just a general style preference for pronounceable code. When I work on an existing codebase that uses a different style, or when my teammates in a new project have strong preferences the other way, I can accept that, of course (not without attempting a little evangelizing in the case of the teammates, though;-).

They are used for formatting strings. %s acts a placeholder for a string while %d acts as a placeholder for a number. Their associated values are passed in via a tuple using the % operator.

name = 'marcog'
number = 42
print '%s %d' % (name, number)

will print marcog 42. Note that name is a string (%s) and number is an integer (%d for decimal).

See https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting for details.

In Python 3 the example would be:

print('%s %d' % (name, number))

It is a formatting character. It tells the formatter to treat the argument as an integer number and format it as such. Other valid formatters could be x to format it as a hexadecimal number, or b for binary, etc.

See the Format String Syntax, and more specifically, the Format Specification Mini-Language:

'd'
Decimal Integer. Outputs the number in base 10.

Each {...} part is a slot, and the positional arguments to the str.format() method are slotted in in the same order.