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]