What is %s in python print?

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'

The % symbol is used in Python with a large variety of data types and configurations. %s specifically is used to perform 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. 

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 Python code illustrates the way of performing string formatting. 

Simple use of %s

Python3

name = "Geek"

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

Output

Hey, Geek!

Multiple %s

Multiple strings can also be appended within a single string using the %s operator. The strings are replaced in the order of their position in the brackets, where ever there is an %s sign. This is illustrated using the following code snippet :

Python3

var1 = "Geek!"

var2 = "Geeks for Geeks"

print("Hello %s Are you enjoying being at %s for preparations." % (var1, var2))

Output

Hello Geek! Are you enjoying being at Geeks for Geeks for preparations.

Mapping strings to %s

However, the number of occurrences of this operator must be equal to the number of strings to replace with after the % sign. Otherwise, an error of the type “TypeError: not enough arguments for format string” is thrown.

Python3

str1 = 'Understanding'

str2 = '%s'

str3 = 'at'

str4 = 'GeeksforGeeks'

final_str = "%s %s %s %s" % (str1, str3, str4)

print("Concatenating multiple strings using Python '%s' operator:\n")

print(final_str)

Error

Traceback (most recent call last):

  File “/home/c7b65fabd2ad00163eba70bbc39685d3.py”, line 8, in

    final_str = “%s %s %s %s” % (str1, str3, str4)

TypeError: not enough arguments for format string

Correct Code

Python3

str1 = 'Understanding'

str2 = '%s'

str3 = 'at'

str4 = 'GeeksforGeeks'

final_str = "%s %s %s %s" % (str1, str2, str3, str4)

print("Concatenating multiple strings using Python '%s' operator:\n")

print(final_str)

Output

Concatenating multiple strings using Python '%s' operator:

Understanding %s at GeeksforGeeks

Order %s using dictionary

The strings are printed in whatever order they are appended using the dictionary key in output.

Python3

dct = {'str1': 'at',

       'str2': 'GeeksforGeeks',

       'str3': 'Understanding',

       'str4': '%s'}

final_str = "%(str3)s %(str4)s %(str1)s %(str2)s" % dct

print("Concatenating multiple strings using Python '%s' operator:\n")

print(final_str)

Output

Concatenating multiple strings using Python '%s' operator:

Understanding %s at GeeksforGeeks

List as a string for %s

A non-string operator can also be formatted using the %s symbol in Python. Tuples can also be both inserted and formatted using this operator. 

Python3

str1 = 'Understanding'

str2 = 'integers'

str3 = 'at'

str4 = 'GeeksforGeeks = '

lst = [1, 2, 3]

final_str = "%s %s %s %s %s" % (str1, str2, str3, str4, lst)

print("Concatenating multiple values using Python '%s' operator:\n")

print(final_str)

Output

Concatenating multiple values using Python '%s' operator:

Understanding integers at GeeksforGeeks =  [1, 2, 3]

What is %s and %D in Python?

What is the difference between %S and %R in Python?