getting a variable name

[db_ozbecool]

How to get the NAME of the passed parameter ?
Eg. in the example below how to get printed , inside my_func() , value = "test_var"

def my_func(aaa):
[INDENT]print aaa     # <---- this will print the VALUE of passed parameter 'aaa' [/INDENT] 
[INDENT]# ..... but how to print the NAME of the 'aaa' above as called by a parent function main() - i.e.

how to make it print 'test_var'[/INDENT]

def main():
[INDENT]test_var = 123[/INDENT]
[INDENT]my_func(test_var)[/INDENT]

Note that I do not want to get 'aaa' printed but 'test_var'

[sneekula]

Local variables are kept in the function's local dictionary which you can access with vars(). To access one function's local dictionary in another function, you have to pass it along:

def my_func(aaa, main_var):
    mvar = [key for key, val in main_var.items() if val==aaa][0]
    print aaa, main_var, mvar  # 123 {'test_var': 123} test_var

def main():
    test_var = 123
    my_func(test_var, vars())

main()

[db_ozbecool]

thanks for a reply but can you re-write the mvar = ... line in more 'beginners' friendly format ? :
mvar = [key for key, val in main_var.items() if val==aaa][0]

i.e. few separate lines so that I would understand what ot does ?
Thanks

[sneekula]

I hope you understand this better:

def main():
    a = 1
    b = 2
    c = 3
    # local variable dictionary
    main_var = vars()
    print main_var  # {'a': 1, 'c': 3, 'b': 2}

    # get the key (variable name) of a certain value, for instance 3
    mvar = [key for key, val in main_var.items() if val==3][0]
    print mvar  # c

    # in somewhat longer form ...
    mvar_list = []
    # extract the key:value pairs from the dictionary
    for key, val in main_var.items():
        # if value is 3 save the key in a list
        if val == 3:
            mvar_list.append(key)
    print mvar_list     # ['c']
    # pick the first item on the list
    print mvar_list[0]  # c

main()

[db_ozbecool]

Great thanks for the time you spent on it. Most appreciated. BTW: where can I find explanation of what this is (from your code above):

... = [key .... ]

i.e. [ followed by a reserved word

[vegaseat]

the code within [] is called list comprehension and it creates a list

...

q = [process(x) for x in somelist if condition(x)]

is a shorthand notation for ...
q = []
for x in somelist:
    if condition(x):
        q.append(process(x))

...

[db_ozbecool]

One more thing :
How to catch (inside my_func()) a situation of receiving a literal value instead of a variable name:
my_func(test_var, vars()) --- > my_func(123, vars())

thus avoiding this error when making a call to main():
< IndexError: list index out of range >

Note: I realize that my_func() is not able to recover the 'key' for literal data passed, but as long as it does not cause a run time error then I would be fine)

[ZZucker]

Nice observation! Trap the error with try/except like this:

def my_func(aaa, main_var=None):
    try:
        mvar = [key for key, val in main_var.items() if val==aaa][0]
        print aaa, main_var, mvar
    except:
        print aaa
    # other code follows
    pass

def main():
    test_var = 123
    my_func(test_var, vars())
    my_func(123, vars())
    my_func(456, vars())
    my_func(123)

main()

"""
my output -->
123 {'test_var': 123} test_var
123 {'test_var': 123} test_var
456
123
"""