Question

I frequently find myself using the following pattern for string formatting.

a = 3
b = 'foo'
c = dict(mykey='myval')

#prints a is 3, b is foo, mykey is myval
print('a is {a}, b is {b}, mykey is {c[mykey]}'.format(**vars()))

That is, I often have the values I need to print in the local namespace, represented by a call to vars(). As I look over my code, however, it seems awfully unpythonic to be constantly repeating the .format(**vars()) pattern.

I’d like to create a function that will capture this pattern. It would be something like the following.

# doesn't work
def lfmt(s):
    """
    lfmt (local format) will format the string using variables
    in the caller's local namespace.
    """
    return s.format(**vars())

Except that by the time I’m in the lfmt namespace, vars() is no longer what I want.

How can I write lfmt so that it executes vars() in the caller’s namespace such that the following code would work as the example above?

print(lfmt('a is {a}, b is {b}, mykey is {c[mykey]}'))

Answer 1

Edit: In order for lfmt to work when called from different namespaces, you’ll need the inspect module. Note, as the documentation warns, the inspect module may not be suitable for production code since it may not work with all implementations of Python

import inspect
def lfmt(s):
    caller = inspect.currentframe().f_back
    return s.format(**caller.f_locals)

a = 3
b = 'foo'
c = dict(mykey='myval')

print(lfmt('a is {a}, b is {b}, mykey is {c[mykey]}'))
# a is 3, b is foo, mykey is myval