Template language questions

[DrChiper]

Due to some noticed template magic in this thread , I have a question to understand some detail. I tried to locate this in the calibre user manual, but was lost.

I have a query for finding books with extra files which works well:

template:"""program: if has_extra_files() then 'yes' else 'no' fi#@#:t:yes"""

In the above mentioned thread, I saw another template query for the same:

template:"""program: has_extra_files()#@#:b:yes"""

In my first example a "t" is used, while the 2nd uses a "b". I do understand that "b" is meant for "boolean", but what is the meaning of the "t"? And when using "b" instead of "t" in my first query template it does not work. Why?

[chaley]

Originally Posted by DrChiper

Due to some noticed template magic in this thread , I have a question to understand some detail. I tried to locate this in the calibre user manual, but was lost.

I have a query for finding books with extra files which works well:

template:"""program: if has_extra_files() then 'yes' else 'no' fi#@#:t:yes"""

In the above mentioned thread, I saw another template query for the same:

template:"""program: has_extra_files()#@#:b:yes"""

In my first example a "t" is used, while the 2nd uses a "b". I do understand that "b" is meant for "boolean", but what is the meaning of the "t"? And when using "b" instead of "t" in my first query template it does not work. Why?

The 't' means 'text compare'. The first template returns either the string 'yes' or the string 'no'. The text test in the template search checks for the value 'yes'. For completeness, the other search types are 'b' (boolean, set/not set), 'n' (numeric), and 'd' (date).

As for 'b', the General Program Mode documentation says:

• In a logical context, any non-empty value is True
• In a logical context, the empty value is False

The 'b' test (boolean, or set/not set) is a logical context.

You can't use 'b' in the first template because both 'yes' and 'no' are non-empty thus True. The check always succeeds.

The second template returns the value of has_extra_files(), which is either the string '1' or the empty string. As said above, the empty string is False in the logical context so the 'b' test works.

FWIW: the second template is somewhat faster. Not much because the performance difference is swamped by the time required to check the library for data files.

[DrChiper]

Thanks for this information, most enlightening

Originally Posted by chaley

The 't' means 'text compare'. The first template returns either the string 'yes' or the string 'no'. The text test in the template search checks for the value 'yes'. For completeness, the other search types are 'b' (boolean, set/not set), 'n' (numeric), and 'd' (date).

I had already some clue that string compare was used, but figured the 't' was used as a placeholder for 'true' (=yes). Oh well. However, I think it would be an user guide improvement to add there the above info. When you are in the know, you can figure out the 't', but is is not explicitly mentioned. Nor is the placeholder "#@#": it is shown, but not really explained.

Originally Posted by chaley

FWIW: the second template is somewhat faster. Not much because the performance difference is swamped by the time required to check the library for data files.

It is definitely faster on my machine, that's why I wanted to grasp the difference so I could understand what was going on.

[chaley]

Originally Posted by DrChiper

I had already some clue that string compare was used, but figured the 't' was used as a placeholder for 'true' (=yes). Oh well. However, I think it would be an user guide improvement to add there the above info. When you are in the know, you can figure out the 't', but is is not explicitly mentioned. Nor is the placeholder "#@#": it is shown, but not really explained.

In most cases template searches are built using the Advanced Search dialog, as the documentation suggests. That is what I do. The tooltips in that dialog explain much of what you can do.

You can use the "Copy the current search into the boxes" in that dialog to see what a search you found elsewhere, e.g., in a forum post, is doing. For example, here is what you see with for your 2nd template search.


As for why it is faster, the 2nd template has a smaller, simpler program: it doesn't use an if/then/else. For smaller libraries or fewer data files, the time to execute the 'if' statement is a larger percentage of the total.