Allow users to pass a full convert() function definition

[simonw]

I think the fix for this is to change the rules about what code is accepted in both the - mode and the literal code string mode: you can pass in a Python expression, OR a fragment that gets turned into a function, OR code that implements its own def convert(value) function. So this would work too:

sqlite-utils convert my.db mytable col1 '
def convert(value):
    return value.upper()
'

Originally posted by @simonw in #353 (comment)

[simonw]

Relevant code:

sqlite-utils/sqlite_utils/cli.py

Lines 2128 to 2135 in 7a43af2

	# If single line and no 'return', add the return
	if "\n" not in code and not code.strip().startswith("return "):
	code = "return {}".format(code)
	where_args = dict(param) if param else []
	# Compile the code into a function body called fn(value)
	new_code = ["def fn(value):"]
	for line in code.split("\n"):
	new_code.append(" {}".format(line))

One way to implement this would be to look to see if the code starts with def ... - but that's not going to work for proper module that start with a docstring or imports.

[simonw]

Maybe attempt to compile their code, and if it fails try again after adding def fn(value): to the start?

[simonw]

Ideally I'd like to show the perfect syntax error messages to the user - but I don't know if it's possible to do this cleanly because the error might occur with their originally entered code OR it might occur after I add def fn(value) to it.

I'm going to punt on that for the moment and tolerate slightly confusing syntax errors.

[simonw]

Here's an example of the new (slightly confusing) error message:

sqlite-utils convert fixtures.db roadside_attractions name '
def foo(value)  
  bar
  baz
'
Error: Syntax error in code:

    def foo(value)

invalid syntax

Another:

sqlite-utils convert fixtures.db roadside_attractions name '$'
Error: Syntax error in code:

    return $

invalid syntax