Python string interpolation example (Like Swift)

formatted.py

import re
import inspect

FORMAT_REGEX = re.compile(r'\\\(([a-zA-Z_]\w*)\)')
def formatted(string, silent=False):
    to_be_replaced = FORMAT_REGEX.findall(string)
    variables = inspect.stack()[1][0].f_locals
    for item in to_be_replaced:
        if item in variables:
            string = string.replace('\({})'.format(item), str(variables[item]))
        elif silent:
            string = string.replace('\({})'.format(item), '')
        else:
            raise NameError('name \'{}\' is not defined'.format(item))
    return string

def func_a():
    foo = 10
    print formatted('foo is \(foo)')

    func_b()

def func_b():
    bar = 20
    print formatted('bar is \(bar)')
    print formatted('foo is \(foo) and bar is \(bar)', silent=True)
    print formatted('foo is \(foo) and bar is \(bar)', silent=False) # An error occurs!

func_a()

# Output
# foo is 10
# bar is 20
# foo is  and bar is 20
# Traceback (most recent call last):
#   ...
# NameError: name 'foo' is not defined