How to print out the name of a variable

Question

in the following code snippet:

import cv2
for color_space in (cv2.COLOR_RGB2HSV,
                    cv2.COLOR_RGB2LUV,
                    cv2.COLOR_RGB2HLS,
                    cv2.COLOR_RGB2YUV,
                    cv2.COLOR_RGB2YCrCb):   
    *print_it_as_name(color_space)*

With which real statement can I replace print_it_as_name such that the output is

cv2.COLOR_RGB2HSV cv2.COLOR_RGB2LUV cv2.COLOR_RGB2HLS cv2.COLOR_RGB2YUV, cv2.COLOR_RGB2YCrCb

Without hardcoding it using if statements?

Just enclose it in quotation marks `''`? If you want to work with variables dynamically you can always use their names as strings and obtain the corresponding values via `getattr`. — a_guest, Feb 27 '17 at 11:19
But I can't help feeling there's a deeper problem here, to which the usual answer is "use a dict". — Daniel Roseman, Feb 27 '17 at 11:24

EDD · Accepted Answer · 2017-02-27T11:34:05.617

1

Ok I've come up with a little hack to work this out using eval:

for color_space in ("cv2.COLOR_RGB2HSV",
                    "cv2.COLOR_RGB2LUV",
                    "cv2.COLOR_RGB2HLS",
                    "cv2.COLOR_RGB2YUV",
                    "cv2.COLOR_RGB2YCrCb"):   
    print(color_space) # prints the name of the variable
    print(eval(color_space)) # prints the actual value of the variable.

Probably not good practice to actually do this, I would recommend the dictionary approach but since you asked for it this way this is how its done.

edited Feb 27 '17 at 11:34

answered Feb 27 '17 at 11:20

EDD

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My bad: I didnt give you the whole problem in my first post. Please see the edit. – Oblomov Feb 27 '17 at 11:26
Ah sorry for canging the rules of the game again: But I wouldnt bother, if I did not want to use the actual statements cv2.COLOR_RGB2HSV... later in the code. So I really want to iterate over these. Is there no reflection module in python? – Oblomov Feb 27 '17 at 11:49
@user1934212 sorry but I have no idea ^^ – EDD Feb 27 '17 at 12:07
@MukeshIngham This is no good use case for `eval`, you should use `getattr` instead. – a_guest Feb 27 '17 at 12:22

shx2 · Answer 2 · 2017-02-27T11:51:44.630

1

As others suggested, use a dict.

import cv2
data = { 'cv2.'+att : getattr(cv2, att)
         for att in ('COLOR_RGB2HSV','COLOR_RGB2LUV',...) }
print(data.keys())

If you need all the COLOR_* attributes, you can avoid the hard coded list:

data = { ... for att in dir(cv2) if att.startswith('COLOR_') }

edited Feb 27 '17 at 11:51

answered Feb 27 '17 at 11:49

shx2

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Thanks, but that really is not the point. I want to iterate over these values and uses these values later in the code, but also print the name of these values out. – Oblomov Feb 27 '17 at 11:51
@user1934212 I see. See my other answer then. – shx2 Feb 27 '17 at 11:55

score 1 · Answer 3 · answered Feb 27 '17 at 11:55

Use a reverse-map, mapping from the value, to its original name (assuming values are unique).

import cv2
reverse_map = { v:k for k,v in dir(cv2) if k.startswith('COLOR_') }
for color_space in (cv2.COLOR_RGB2HSV,
                    cv2.COLOR_RGB2LUV,
                    cv2.COLOR_RGB2HLS,
                    cv2.COLOR_RGB2YUV,
                    cv2.COLOR_RGB2YCrCb):   
    print(reverse_map[color_space])

How to print out the name of a variable

3 Answers3