better error when missing CTE

[edublancas]

when using the --with argument, this runs; however, if the passed key does not exist, the error traceback is pretty long (see attached notebook).

Instead, we should raise an UsageError:

from IPython.core.error import UsageError

raise UsageError(f"{key!r} is not a valid snippet identifier")

To provide a more helpful message, we can also use difflib to check if there are any closes matches:

"subsett" is not a valid snippet identifier. Did you mean "subset"?

If there are no close matches, we can display all available keys:

"subsett" is not a valid snippet identifier. Valid identifiers are "one", "another", and "something"

[edublancas]

sample notebook: sample.ipynb.zip

[anupam-tiwari]

I can look into it!

[anupam-tiwari]

regarding this: "To provide a more helpful message, we can also use difflib to check if there are any closes matches:"

The function difflib.get_close_matches(word, possibilities, n=3, cutoff=0.6) takes parameter possibilities as a list of sequences against which to match word, since key can be user defined example %%sql --save anupam I was wondering how should I pass on the possibilities list as there can be wide range of strings to compare from! am I doing something wrong here?

[anupam-tiwari]

I think I will return the best match if it exist or else return the entire keys:

if key not in self._data: 
            matches = difflib.get_close_matches(key, self._data)
            if matches: 
                raise UsageError(f"{key!r} is not a valid snippet identifier. Did you mean {matches[0]!r}?")
            else: 
                valid = ", ".join(f'"{key}"' for key in self._data.keys())
                raise UsageError(f"{key!r} is not a valid snippet identifier. Valid identifiers are {valid}.")

is this is a sound approach?