Determine Original Name of Variable After Its Passed to a Function

Determine original name of variable after its passed to a function

You're right, this is very much impossible in any sane way, since only the value gets passed into the function.

How to get the original variable name of variable passed to a function

You can't. It's evaluated before being passed to the function. All you can do is pass it as a string.

How to find the name of a variable that was passed to a function?

Not really solution, but may be handy (anyway you have echo('foo') in question):

def echo(**kwargs):
    for name, value in kwargs.items():
        print name, value

foo = 7
echo(foo=foo)

UPDATE: Solution for echo(foo) with inspect

import inspect
import re

def echo(arg):
    frame = inspect.currentframe()
    try:
        context = inspect.getframeinfo(frame.f_back).code_context
        caller_lines = ''.join([line.strip() for line in context])
        m = re.search(r'echo\s*\((.+?)\)$', caller_lines)
        if m:
            caller_lines = m.group(1)
        print caller_lines, arg
    finally:
        del frame

foo = 7
bar = 3
baz = 11
echo(foo)
echo(foo + bar)
echo((foo + bar)*baz/(bar+foo))

Output:

foo 7
foo + bar 10
(foo + bar)*baz/(bar+foo) 11

It has the smallest call, but it's sensitive to newlines, e.g.:

echo((foo + bar)*
      baz/(bar+foo))

Will print:

baz/(bar+foo)) 11

get the variable name passed to a function in C

You can't print the address of a variable using function like you've shown. The reason is that a is local variable, which has a different identity than the variable whose value you passed to printAddress.

You also can't get the name, because the name doesn't exist in that context.

However, you could use a macro:

#define printAddress(x)    printf("Address of variable %s is %p\n", #x, &x)

Note that # here is the stringification operator of the preprocessor; it turns a token into a C string literal (effectively just adding quotes around the token).

Full example:

#include <stdio.h>

#define printAddress(x)    printf("Address of variable %s is %p\n", #x, &x)

int main(void)
{
    int foo;
    printAddress(foo);
    return 0;
}

original variable name passed to function?

It's not possible. Even pass-by-reference won't help you. You'll have to pass the name as a second argument.

But what you have asked is most assuredly not a good solution to your problem.

Get Original Variable Name From Function in Ruby

Implementation of the idea from the comment, but I reiterate that it's extremely fragile and a really bad idea all around.

def orig_var_name(var)
  loc = caller_locations.first
  line = File.read(loc.path).lines[loc.lineno - 1]
  line[/#{__method__}\(\s*(\w+)\s*\)/, 1]
rescue Errno::ENOENT
  raise "Not usable from REPL"
end

foo = 1
puts orig_var_name(foo)
# => foo

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