如何打印变量的名称和值？

Question

This is what I have in mind because I find myself typing the name twice whenever I want to inspect the value of a variable:

a = 1
my_print(a)  # "a: 1"

Is this possible in Python?

Answer 1

If you are in control of the calling function, you can hack this to work reasonably well like:

Code:

import inspect

def print_name_and_value(var):
    lines = inspect.stack()[1][4]
    var_name = ''.join(lines).strip().split('(')[-1].split(')')[0]
    print("%s: %d" % (var_name, var))

a = 5
print_name_and_value(a)

Results:

a: 5

How does this work?

The inspect module can be used to inspect the caller, and get the line of code used by the caller. With a bit of string hacking the variable name (assuming it is a simple variable and not a more complex expression) can be gathered from the source code.

Answer 2

I would say "no", and any other magic doable is just... too much magic.

However there's something you can do, and that's looking at the stack trace using the inspect module .

import inspect


def my_print(thingy):
    # print("id(thingy)=%s" % id(thingy))
    previous_frame = inspect.currentframe().f_back
    # print("locals: %s" % previous_frame.f_locals)
    for variable_name, variable_value in previous_frame.f_locals.items():
        if id(variable_value) == id(thingy):
            return("%s: %s" % (variable_name, variable_value))

    # print("globals: %s" % previous_frame.f_globals)
    for variable_name, variable_value in previous_frame.f_globals.items():
        if id(variable_value) == id(thingy):
            return("%s: %s" % (variable_name, variable_value))


if __name__ == '__main__':
    a = 1
    print("Test %s" % my_print(a))  # "a: 1"
    list_thingy = [1, 2, 3]
    print("Test %s" % my_print(list_thingy))

    def and_within_function():
        d = {1: "a"}
        print("Test %s" % my_print(d))

    and_within_function()

But this is not reliable and I'd use it more as a curiosity , since there are plenty of "special cases". For instance: the first 255 integers (I think) in Python occupy a specific memory address so, if you have two variables that are =1 I don't think you're gonna really be guaranteed which one is it.