issues: 1575131737
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| 1575131737 | I_kwDOCGYnMM5d4ppZ | 525 | Repeated calls to `Table.convert()` fail | 167893 | closed | 0 | 4 | 2023-02-07T22:40:47Z | 2023-05-08T21:59:41Z | 2023-05-08T21:54:02Z | CONTRIBUTOR | ## Summary When using the API, repeated calls to `Table.convert()` do not work correctly since all conversions quietly use the callable (function, lambda) from the first call to `convert()` only. Subsequent invocations with different callables use the callable from the first invocation only. ## Example ```python from sqlite_utils import Database db = Database(memory=True) table = db['table'] col = 'x' table.insert_all([{col: 1}]) print(table.get(1)) table.convert(col, lambda x: x*2) print(table.get(1)) def zeroize(x): return 0 #zeroize = lambda x: 0 #zeroize.__name__ = 'zeroize' table.convert(col, zeroize) print(table.get(1)) ``` Output: ``` {'x': 1} {'x': 2} {'x': 4} ``` Expected: ``` {'x': 1} {'x': 2} {'x': 0} ``` ## Explanation This is some relevant [documentation](https://github.com/simonw/sqlite-utils/blob/1491b66dd7439dd87cd5cd4c4684f46eb3c5751b/docs/python-api.rst#registering-custom-sql-functions:~:text=By%20default%20registering%20a%20function%20with%20the%20same%20name%20and%20number%20of%20arguments%20will%20have%20no%20effect). * `Table.convert()` takes a `Callable` to perform data conversion on a column * The `Callable` is passed to `Database.register_function()` * `Database.register_function()` uses the callable's `__name__` attribute for registration * (Aside: all lambdas have a `__name__` of `<lambda>`: I thought this was the problem, and it was close, but not quite) * However `convert()` first wraps the callable by local function [`convert_value()`](https://github.com/simonw/sqlite-utils/blob/fc221f9b62ed8624b1d2098e564f525c84497969/sqlite_utils/db.py#L2661) * Consequently `register_function()` sees name `convert_value` for all invocations from `convert()` * `register_function()` silently ignores registrations using the same name, retaining only the first such registration There's a mismatch between the comments and the code: https://github.com/simonw/sqlite-utils/blob/fc221f9b62ed8624b1d2098e564f525c84497969/sqlite_utils/db.py#L404 but actually the existing function is returned/used instead (as the "registering custom sql functions" doc I linked above says too). Seems like this can be rectified to match the comment? ## Suggested fix I think there are four things: 1. The call to `register_function()` from `convert()`should have an explicit `name=` parameter (to continue using `convert_value()` and the progress bar). 2. For functions, this name can be the real function name. (I understand the sqlite api needs a name, and it's nice if those are recognizable names where possible). For lambdas would `'lambda-{uuid}'` or similar be acceptable? 3. `register_function()` really should throw an error on repeated attempts to register a duplicate (function, arity)-pair. 4. A test? I haven't looked at the test framework here but seems this should be testable. ## See also - #458 | 140912432 | issue | {"url": "https://api.github.com/repos/simonw/sqlite-utils/issues/525/reactions", "total_count": 0, "+1": 0, "-1": 0, "laugh": 0, "hooray": 0, "confused": 0, "heart": 0, "rocket": 0, "eyes": 0} | completed |