Getting key arguments from prepared string [duplicate]

Question

I have a prepared string, e.g. my_string = 'My name is {name}.'

and I have dictionary of kwargs, such as:

format_kwargs = {
    'name': 'John',
    ...
}

So that I can format the string in this manner: my_string.format(**format_kwargs)

That is all good. The problem is that I want to determine what keys are in the string, so that I do not calculate the kwargs needlessly. That is, I have a set of keywords used in these strings by default, but not all of them are used in all strings. They are basically regular messages shown to user, such as '{name}, you account was successfully created!'.

I want to do something like:

format_kwargs = {}

if 'name' in <my_string.keys>:
    format_kwargs['name'] = self.get_user().name
if '...' in <my_string.keys>:
    format_kwargs['...'] = some_method_...()

my_string.format(**format_kwargs)

How do I retrieve the keys?

EDIT:

a simple if 'name' in my_string does not work because that would also match something like {parent_name} or 'The name change was not successful.'

Answer 1

Use string.Formatter

from string import Formatter
s = 'Hello {name}. Are you {debil_status}'
keys = [i[1] for i in Formatter().parse(s)]
print keys

>>> ['name', 'debil_status']