String interpolation in Python 2 using `eval` and `inspect` to get caller's locals.

fmt.py

import inspect
import re

def fmt(s):
    """
    Interpolate arbitrary expressions inside '{}' in strings (similar to Ruby or Scala).
    It should go without saying that because this uses `eval`, it is unsafe to use with any user-provided inputs.
    It is also probably terribly slow because it's using `inspect` to get the caller's local variables.
    
    Example:
        x = 1
        print fmt('x is {x}, x+1 is {x+1}')
        > x is  1, x+1 is 2
    """
    caller_locals = inspect.currentframe().f_back.f_locals
    return re.compile(r"{(.*?)}").sub(lambda m: str(eval(m.group(1), globals(), caller_locals)), str(s))