How to associate a code block to another one so that it is executed beforehand?

How to associate a code block to another one so that it is executed beforehand?

[Rodrigo Morales]

Is it possible to associate a code block (A) to another code block (B)
so that when (A) is executed (B) is executed beforehand? I'm asking this
because I have a bash code block (B) that creates a file that is then
processed by a python code block (A) so before executing (A) block, the
file needs to be created by (B).

I managed to accomplish this only with shell code blocks by creating a
function that gets a code block as an string but now that code blocks
have different languages (bash and python) I can't use this same
approach. Recall that ":prologue" inserts an string at the beginning of
the code block (see minimal working example of this idea below.)

#+NAME: create-file
#+begin_src bash :results silent
cat << EOF > main.txt
foo
bar
EOF
#+end_src

#+HEADER: :prologue (org-babel-get-block-as-string "create-file")
#+begin_src bash
cat main.txt
#+end_src

#+RESULTS:
#+begin_example
foo
bar
#+end_example

-- 
Rodrigo Morales.
IRC: rdrg109 (freenode)

Re: How to associate a code block to another one so that it is executed beforehand?

[John Kitchin]

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Here is one way to do it.  You use a :var to "run" the other block.

#+NAME: create-file
#+begin_src bash :results silent
cat << EOF > main.txt
foo
bar
EOF
#+end_src

#+BEGIN_SRC python :var run=create-file
with open('main.txt') as f:
    print(f.read())
#+END_SRC

#+RESULTS:
: foo
: bar
:

John

-----------------------------------
Professor John Kitchin
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803
@johnkitchin
http://kitchingroup.cheme.cmu.edu



On Mon, Feb 15, 2021 at 4:01 PM Rodrigo Morales <
moralesrodrigo1100@gmail.com> wrote:

>
> Is it possible to associate a code block (A) to another code block (B)
> so that when (A) is executed (B) is executed beforehand? I'm asking this
> because I have a bash code block (B) that creates a file that is then
> processed by a python code block (A) so before executing (A) block, the
> file needs to be created by (B).
>
> I managed to accomplish this only with shell code blocks by creating a
> function that gets a code block as an string but now that code blocks
> have different languages (bash and python) I can't use this same
> approach. Recall that ":prologue" inserts an string at the beginning of
> the code block (see minimal working example of this idea below.)
>
> #+NAME: create-file
> #+begin_src bash :results silent
> cat << EOF > main.txt
> foo
> bar
> EOF
> #+end_src
>
> #+HEADER: :prologue (org-babel-get-block-as-string "create-file")
> #+begin_src bash
> cat main.txt
> #+end_src
>
> #+RESULTS:
> #+begin_example
> foo
> bar
> #+end_example
>
> --
> Rodrigo Morales.
> IRC: rdrg109 (freenode)
>
>

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Re: How to associate a code block to another one so that it is executed beforehand?

[Rodrigo Morales]

John Kitchin <jkitchin@andrew.cmu.edu> writes:

> Here is one way to do it.  You use a :var to "run" the other block.

Thank you very much for the suggestion. It indeed works but I think that
I don't need what I was requesting now that I've found out about the
=:post= header argument.e

After reading your answer, I remembered that there exists the =:post=
header argument and that fully changed the way I was taking notes.

This is how my notes looked like

#+begin_src org
,#+NAME: create-file-foo
,#+begin_src dash :results silent
cat << EOF > main.txt
foo first
foo second
EOF
,#+end_src

,#+NAME: create-file-bar
,#+begin_src dash :results silent
cat << EOF > main.txt
bar first
bar second
EOF
,#+end_src

The following code block prints each line the corresponding index and the length of the specified file.

# ====================================================================
# Here I wanted to call one of the code blocks presented above so that
# before the Python code block is executed, the file is created.
# ====================================================================

,#+begin_src python
with open('main.txt') as f:
    for line in f:
        print(line, end='')
,#+end_src
#+end_src

Now using the =:post= header argument my notes look like

#+begin_src org
We can print each line together with its index by executing

,#+NAME: read-file-with-index
,#+begin_src python
with open('main.txt') as file:
    for idx,line in enumerate(file):
        print(idx, line, end='')
,#+end_src

,#+begin_src dash :post read-file-with-index()
cat << EOF > main.txt
foo first
foo second
EOF
,#+end_src

,#+RESULTS:
,#+begin_example
0 foo first
1 foo second
,#+end_example

,#+begin_src dash :post read-file-with-index()
cat << EOF > main.txt
bar first
bar second
EOF
,#+end_src

,#+RESULTS:
,#+begin_example
0 bar first
1 bar second
,#+end_example
#+end_src

Note that, in this scenario, when using the =:post= header argument it
is only necessary to name the Python code block instead of naming all
the code blocks that are meant to be processed by the Python script.

-- 
Rodrigo Morales.
IRC: rdrg109 (freenode)