a REPL for development

[justin2004]

Hi all,

I am making some new commands and I kept finding myself doing this:

# BaseSheet.addCommand('1', 'hello-world', 'status(dir(sheet))')
BaseSheet.addCommand('1', 'hello-world', 'status(sheet.cursorCell.text)')

that is, using the status window as a console log to see what functions/attributes objects have.
But that requires that I save .visidatarc and re-run vd.

I really wanted a REPL for this so I put this into my .visidatarc.

BaseSheet.addCommand('', 'REPL', """
import subprocess
import pprint
with SuspendCurses():
    pp = pprint.PrettyPrinter(indent=4).pprint
    # now you can `pp(dir(sheet))` for example
    while True:
        try:
            # print(eval(input(">>> "))) # this works if you don't want expression history
            print(eval(subprocess.run(['rlwrap','--one-shot','--substitute-prompt',">>> ",'cat'], text=True, capture_output=True).stdout))
        except Exception as e:
            # print(f"Error: {e}")
            print(e)
            break
""")

You'll first want to apt-get install rlwrap and if you like vim I would put this in ~/.inputrc:

set editing-mode vi

Now I can inspect stuff at the REPL and the jump back into vd at the sheet where I left off.
e.g.
from a sheet I do <space>REPL<enter>

more usefully:

I'd like to fix the exception handling:

Ideally we'd catch the EOF and return quietly and for syntax errors i'd like to continue and stay in the REPL.
Can anyone see the problem with that?

Well I hope this helps someone else too!

Note, I know about the exec-python command but you don't get command/expression history and it doesn't feel REPLy.

[ajkerrigan]

Using an rlwrap subprocess is a clever idea, I dig it!

I also found myself often wanting a REPL which led to the vdrepl plugin. That's a different approach with different assumptions/dependencies though. I haven't touched it because it still works, but it could probably use a cleanup pass.

Your method seems to work smoothly out of the box for me 💪 . Regarding the name 'e' is not defined error, I know scoping can get pretty funky with the timing of evals and stuff. A couple tweaks like this seem to help dodge that issue, allow you to catch/display "real" errors, and silently exit back to vd on ^D or ^C:

import subprocess
import pprint

def rlwrap_repl():
    with SuspendCurses():
        pp = pprint.PrettyPrinter(indent=4).pprint
        while True:
            try:
                source = subprocess.run(['rlwrap','--one-shot','--substitute-prompt',">>> ",'cat'], text=True, capture_output=True).stdout
                if not source:
                    break
                print(eval(source))
            except (EOFError, KeyboardInterrupt):
                break
            except Exception as e:
                print(e)
                continue

BaseSheet.addCommand('', 'REPL', 'rlwrap_repl()')

[justin2004]

thanks, @ajkerrigan !

when i was looking for a vd repl i didn't find your plugin. i'll try it out too!

[saulpw]

Since multiple people want a REPL for VisiData like this, what do y'all think about combining the best ideas from @justin2004's code and @ajkerrigan's vdrepl plugin and pulling them into the vd repo formally?

[justin2004]

@saulpw , sounds good!

note that i had to update mine to allow statements (like assignment):

            except SyntaxError as e:
                # `source` might have been a statement (like assignment)
                exec(source)

[ajkerrigan]

Sounds good to me! Not sure the best way to combine things, but after using both side by side for a bit I realized my take wasn't bringing as many variables into the local scope. Tweaked that.

Some other thoughts:

• I think @justin2004 's implementation feels closer to vd's normal exec-python semantics, where ptipython might be heavier than most people want.
• rlwrap seems quick/easy to install across multiple platforms via apt/brew/etc 👍 . my approach leans on ptpython/ptipython being installed via pip. From the vd maintenance perspective does one fit better than the other? Feels pretty user-dependent to me, both totally valid.
• A formal repl should probably offer a history file option, but default to something inside the visidata dir (~/.visidata/cache/repl_history or something?)
  • After writing this reply I came across [stored] automatically save input history by default #2298 (comment) which seems relevant for this

[saulpw]

BTW did y'all know about the Ctrl+Y family of commands? They pull up a sheet with the row/cell/sheet of the attributes of the underlying Python object.

[frosencrantz]

@saulpw what happened with this feature:? It looks like it did not get added this year. I can add a feature request to track this, if that would help any.