How can I avoid the format string?

Question

Is it possible to use Python syntax str.format(key=value) to replace only certain keys.

Consider the following example:

 my_string = 'Hello {name}, my name is {my_name}!' my_string = my_string.format(name='minerz029') 

which returns

 KeyError: 'my_name' 

Is there any way to achieve this?

Answer 1

A slightly simpler workaround that I use:

 my_string = 'Hello {name}, my name is {my_name}!' to_replace = { "search_for" : "replace_with", "name" : "minerz029", } for search_str in to_replace: my_string = my_string.replace('{' + search_str + '}', to_replace[search_str]) print(my_string) 

This can easily be expanded with more keys in the to_replace dict and will not complain even if the search string does not exist. It could probably be improved to offer more .format() functions, but that was enough for me.

Answer 2

You can escape my_name using double curly braces, e.g.

 >>> my_string = 'Hello {name}, my name is {{my_name}}!' >>> my_string.format(name='minerz029') 'Hello minerz029, my name is {my_name}!' 

As you can see, after formatting, the external {} is deleted once and {{my_name}} becomes {my_name} . If you later want to format my_name , you can just format it again, for example

 >>> my_string = 'Hello {name}, my name is {{my_name}}!' >>> my_string = my_string.format(name='minerz029') >>> my_string 'Hello minerz029, my name is {my_name}!' >>> my_string.format(my_name='minerz029') 'Hello minerz029, my name is minerz029!' 

Answer 3

Python3.2 + has a format_map that allows you to do this

 >>> class D(dict): ... def __missing__(self, k):return '{'+k+'}' ... >>> my_string = 'Hello {name}, my name is {my_name}!' >>> my_string.format_map(D(name='minerz029')) 'Hello minerz029, my name is {my_name}!' >>> _.format_map(D(my_name='minerz029')) 'Hello minerz029, my name is minerz029!' 

Now there is no need to add additional {} , only the keys that you point to D will be replaced

As @steveha points out, if you are using older Python3, you can still use

 my_string.format(**D(name='minerz029'))