String Replacement Fields in Python

The Python String .format() Method

Here we will learn string.format() method which is very useful to do formatting in string dynamically by replacing placeholder with values we provide.

Syntax

.format(<positional_argument(s)>, <keyword_argument(s)>)

Note that it is a technique, not an operator. The < template > method, which is a string containing the replacement fields, is called. The method specifies < positional arguments > and < keyword arguments > values that are inserted into < template > instead of the replacement fields. The resulting formatted string is the return value of the method.

Replacement fields are enclosed in curly braces ({}) in the < template > string.A literal text that is copied directly from the template to the output is anything not contained in curly braces. If you need to include, in the template string, a literal curly bracket character, such as {or}, then you can escape this character by doubling:

>>> '{{ {0} }}'.format('Hello')
'{ Hello }'

Now lets talk about arguments, there are two ways to pass the arguments in string.format() method:

1. Positional Arguments:

Positional arguments are inserted instead of numbered replacement fields into the template. Like list indexing, replacement field numbering is zero-based. The number of the first positional argument is 0, the number of the second is 1, and so on:

>>> '{0}/{1}/{2}'.format( 'indb',  'ndls',  '007')
 'indb/ndls/007'

Note that replacement fields don’t have to appear in numerical order in the template. In any order, they can be specified, and they can appear more than once:

>>>  '{2}.{1}.{0}/{0}{0}.{1}{1}.{2}{2}'.format('indb', 'ndls', '007')
 '007.ndls.indb/indbindb.ndlsndls.007007'

The numbers in the substitute fields can be omitted, in which case the interpreter assumes a sequential order. This is known as automatic numbering of a field:

>>> '{}/{}/{}'.format('indb', 'ndls', '007')
 'foo/bar/baz'