format() function is similar to the String format method. Internally, both methods call
__format__() method of an object.
While the built-in
format() function is a low level implementation for formatting an object using
__format__() internally, string
format() is a higher level implementation able to perform complex formatting operations on multiple object strings as well.
The syntax of format() is:
format() function takes two parameters:
- value - value that needs to be formatted
- format_spec - The specification on how the value should be formatted.
The format specifier could be in the format:
[[fill]align][sign][#][width][,][.precision][type] where, the options are fill ::= any character align ::= "<" | ">" | "=" | "^" sign ::= "+" | "-" | " " width ::= integer precision ::= integer type ::= "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"
Return value from format()
format() function returns a formatted representation of a given value specified by the format specifier.
Example 1: Number formatting with format()
# d, f and b are type # integer print(format(123, "d")) # float arguments print(format(123.4567898, "f")) # binary format print(format(12, "b"))
123 123.456790 1100
Example 2: Number formatting with fill, align, sign, width, precision and type
# integer print(format(1234, "*>+7,d")) # float number print(format(123.4567, "^-09.3f"))
Here, when formatting the integer
1234, we've specified the formatting specifier
*>+7,d. Let's understand each option:
*- It is the fill character that fills up the empty spaces after formatting
>- It is the right alignment option that aligns the output string to the right
+- It is the sign option that forces the number to be signed (having a sign on its left)
7- It is the width option that forces the number to take a minimum width of 7, other spaces will be filled by fill character
,- It is the thousands operator that places a comma between all thousands.
d- It is the type option that specifies the number is an integer.
When formatting the floating point number
123.4567, we've specified the format specifier
^-09.3f. These are:
^- It is the center alignment option that aligns the output string to the center of the remaining space
-- It is the sign option that forces only negative numbers to show the sign
0- It is the character that is placed in place of the empty spaces.
9- It is the width option that sets the minimum width of the number to 9 (including decimal point, thousands comma and sign)
.3- It is the precision operator that sets the precision of the given floating number to 3 places
f- It is the type option that specifies the number is a float.
Example 3: Using format() by overriding __format__()
# custom __format__() method class Person: def __format__(self, format): if(format == 'age'): return '23' return 'None' print(format(Person(), "age"))
When you run the program, the output will be:
Here, we have overridden the
__format__() method of the class
It now accepts a
format parameter and returns 23 if it is equal to
'age'. If no format is specified,
None is returned.
format() function internally runs
Person().__format__("age") to return 23.