NameError in filter

[UlyssesZh]

target[src] and content[src] appear in the output of -K, but using them causes NameError (none of target, content, src is defined). Is this a bug? Or did I do something wrong?
I was trying to download something from DeviantArt by filtering by source url.

[mikf]

-K shows the syntax used in format strings. In actual Python code (--filter), you need to put those key values in quotes to make them strings: target['src']. target.get('src') would also work.

[UlyssesZh]

I see. I think it is better to clarify that in the output of -K.

[mikf]

Do you have an idea or a suggestion how? The output is already cluttered as is.
I also kind of expect users to know the difference between format strings and Python expressions and how to access data when using "advanced" stuff in --filter.

Alternatively, you can use -j --range 1 to get a better(?) look at the actual data and how it is structured, or you specify a name for the download URL value and use that: -o url-metadata=dlurl --> --filter "print(dlurl)"

[UlyssesZh]

Oh! I found a case where there is unexpected NameError. The minimum reproducing code is:

gallery-dl --filter "any(map(lambda s: extension, ['']))" deviantart.com/ayyasap

Output:

[deviantart][error] FilterError: Evaluating filter expression failed (NameError: name 'extension' is not defined)

[UlyssesZh]

Do you have an idea or a suggestion how? The output is already cluttered as is.

What about this: in the output of -K, change

Keywords for filenames and --filter:
------------------------------------

into

Keywords for filenames and --filter (for use in filters, add quotes to the keys):
------------------------------------

or other wordings.