What are %s %d in python?

These are all informative answers, but none are quite getting at the core of what the difference is between %s and %d.

%s tells the formatter to call the str() function on the argument and since we are coercing to a string by definition, %s is essentially just performing str(arg).

%d on the other hand, is calling int() on the argument before calling str(), like str(int(arg)), This will cause int coercion as well as str coercion.

For example, I can convert a hex value to decimal,

>>> '%d' % 0x15
'21'

or truncate a float.

>>> '%d' % 34.5
'34'

But the operation will raise an exception if the argument isn't a number.

>>> '%d' % 'thirteen'
Traceback (most recent call last):
  File "", line 1, in 
TypeError: %d format: a number is required, not str

So if the intent is just to call str(arg), then %s is sufficient, but if you need extra formatting (like formatting float decimal places) or other coercion, then the other format symbols are needed.

With the f-string notation, when you leave the formatter out, the default is str.

>>> a = 1
>>> f'{a}'
'1'
>>> f'{a:d}'
'1'
>>> a = '1'
>>> f'{a:d}'
Traceback (most recent call last):
  File "", line 1, in 
ValueError: Unknown format code 'd' for object of type 'str'

The same is true with string.format; the default is str.

>>> a = 1
>>> '{}'.format(a)
'1'
>>> '{!s}'.format(a)
'1'
>>> '{:d}'.format(a)
'1'

In this article, we will see the difference between %s and %d in Python. Here, we start with the proper explanation of one at a time, then both, and at last compare these.

What does %s do in Python?

The % symbol is used in Python with a large variety of data types and configurations. It is used as an argument specifier and string formatter. %s specifically is used to perform the concatenation of strings together. It allows us to format a value inside a string. It is used to incorporate another string within a string. It automatically provides type conversion from value to string.

How to Use %s in Python

The %s operator is put where the string is to be specified. The number of values you want to append to a string should be equivalent to the number specified in parentheses after the % operator at the end of the string value. The following code illustrates the usage of the %s symbol :

Python3

name = "Geek"

print("Hey, %s!" % name)

Output

Hey, Geek!

What does %d do in Python? 

The %d operator is used as a placeholder to specify integer values, decimals, or numbers. It allows us to print numbers within strings or other values. The %d operator is put where the integer is to be specified. Floating-point numbers are converted automatically to decimal values. 

Python3

num = 2021

print("%d is here!!" % num)

Output

2021 is here!!

How to Use %d in Python

The decimal and rational numbers are rounded off to the absolute integral part and the numbers after the decimal are scraped off, that is only the integers are extracted. The following code illustrates the usage of %d with decimal and fractional numbers:

Python3

frac_num = 8/3

print("Rational number formatting using %d")

print("%d is equal to 8/3 using this operator." % frac_num)

dec_num = 10.9785

print("Decimal number formatting using %d")

print("%d is equal to 10.9785 using this operator." % dec_num)

Output

Rational number formatting using %d
2 is equal to 8/3 using this operator.
Decimal number formatting using %d
10 is equal to 10.9785 using this operator.

Difference Between %s and %d?

We can use a combination of operators also within a single program. Before that first, clear some concepts by comparing as given below :

Common Errors Using %s and %d

Example 1:

The %s automatically converts a numeric value to a string without throwing an error. 

Python3

name = "Sita"

age = 22

print("Using %s ")

print ("%s's age is %s."%(name,age))

Output

Using %s 
Sita's age is 22.

Example 2:

 The %d, however, can only be used for numeric values. Otherwise, an error is returned. 

Python3

name = "Sita"

age = 22

print("Using %d")

print ("%d's age is %d."%(name,age))

Error

Using %d
Traceback (most recent call last):
 File "", line 4, in 
TypeError: %d format: a number is required, not str