Python String Formatting

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format() method allows you format string in any way you want.

Syntax: template.format(p1, p1, .... , k1=v1, k2=v2)

template is a string containing format codes, format()  method uses it’s argument to substitute value for each format codes. For e.g

{0}  and {1}  are format codes. The format code {0}  is replaced by the first argument of format()  i.e 12 , while {1}  is replaced by the second argument of format()  i.e 31 .

Expected Output:

This technique is okay for simple formatting but what if you want to specify precision in floating point number ? For such thing you need to learn more about format codes. Here is the full syntax of format codes.

Syntax: {[argument_index_or_keyword]:[width][.precision][type]}

type  can be used with format codes

Format codes Description
d for integers
f for floating point numbers
b for binary numbers
o for octal numbers
x for octal hexadecimal numbers
s for string
e for floating point in exponent format

Following examples will make things more clear.

Example 1:

Here we specify 2  digits of precision and f  is used to represent floating point number.

Expected Output:

Example 2

Here we specify 3  digits of precision, 10  for width and f  for floating point number.

Expected Output:

Example 3:

here d  in {1:d} represents integer value.

Expected Output:

You need to specify precision only in case of floating point numbers if you specify precision for integer ValueError  will be raised.

Example 5:

Expected Output:

Example 6:

Expected Output:

Example 7:

Expected Output:

Example 8:

Expected Output:

format()  method also supports keywords arguments.

Note while using keyword arguments we need to use arguments inside {}  not numeric index.

You can also mix position arguments with keywords arguments

format()  method of formatting string is quite new and was introduced in python 2.6 . There is another old technique  you will see in legacy codes which allows you to format string using %  operator instead of format()  method.

Let’s take an example.

Here we are using template string on the left of % . Instead of {} for format codes we are using % . On the right side of % we use tuple to contain our values. %d and %.2f are called as format specifiers, they begin with % followed by character that represents the data type. For e.g %d  format specifier is a placeholder for a integer, similarly %.2f  is a placeholder for floating point number.

So %d  is replaced by the first value of the tuple i.e 12  and %.2f  is replaced by second value i.e 150.87612 .

Expected Output:

Some more examples

Example 1:

New: "{0:d} {1:d} ".format(12, 31)

Old: "%d %d" % (12, 31)

Expected Output:

Example 2:

New: "{0:.2f} {1:.3f}".format(12.3152, 89.65431)

Old "%.2f %.3f" % (12.3152, 89.65431)

Expected Output:

Example 3:

New: "{0:s} {1:o} {2:.2f} {3:d}".format("Hello", 71, 45836.12589, 45 )

Old:  "%s %o %.2f %d" % ("Hello", 71, 45836.12589, 45 )

Expected Output:


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7 thoughts on “Python String Formatting

    1. admin Post author

      width specifier is used to data in particular format. Let’s say you set the width of 10 but the length of the number to be output is 3, then in this case 7 leading spaces will be added.

    1. admin Post author

      *array is used to unpack the elements of an array.and send individual elements to placeholders like {0}, {1} and so on

      Similarly **d is used to unpack elements of a dictionary.


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