`sqlite_utils.utils.TypeTracker` should be a documented API

[simonw]

I've used it in a couple of external places now:

• https://github.com/simonw/datasette-socrata/blob/32fb256a461bf0e790eca10bdc7dd9d96c20f7c4/datasette_socrata/__init__.py#L264-L280
• https://github.com/simonw/datasette-lite/blob/caa8eade10f0321c64f9f65c4561186f02d57c5b/webworker.js#L55-L64

Refs:

• Ability to load CSV from a URL datasette-lite#32

[simonw]

Code to document:

sqlite-utils/sqlite_utils/utils.py

Lines 318 to 331 in 3fbe8a7

	class TypeTracker:
	def __init__(self):
	self.trackers = {}
	def wrap(self, iterator):
	for row in iterator:
	for key, value in row.items():
	tracker = self.trackers.setdefault(key, ValueTracker())
	tracker.evaluate(value)
	yield row
	@property
	def types(self):
	return {key: tracker.guessed_type for key, tracker in self.trackers.items()}

[simonw]

I also added inline documentation and types:

sqlite-utils/sqlite_utils/utils.py

Lines 318 to 360 in 773f2b6

	class TypeTracker:
	"""
	Wrap an iterator of dictionaries and keep track of which SQLite column
	types are the most likely fit for each of their keys.
	Example usage:
	.. code-block:: python
	from sqlite_utils.utils import TypeTracker
	import sqlite_utils
	db = sqlite_utils.Database(memory=True)
	tracker = TypeTracker()
	rows = [{"id": "1", "name": "Cleo", "id": "2", "name": "Cardi"}]
	db["creatures"].insert_all(tracker.wrap(rows))
	print(tracker.types)
	# Outputs {'id': 'integer', 'name': 'text'}
	db["creatures"].transform(types=tracker.types)
	"""
	def __init__(self):
	self.trackers = {}
	def wrap(self, iterator: Iterable[dict]) -> Iterable[dict]:
	"""
	Use this to loop through an existing iterator, tracking the column types
	as part of the iteration.
	:param iterator: The iterator to wrap
	"""
	for row in iterator:
	for key, value in row.items():
	tracker = self.trackers.setdefault(key, ValueTracker())
	tracker.evaluate(value)
	yield row
	@property
	def types(self) -> Dict[str, str]:
	"""
	A dictionary mapping column names to their detected types. This can be passed
	to the ``db[table_name].transform(types=tracker.types)`` method.
	"""
	return {key: tracker.guessed_type for key, tracker in self.trackers.items()}

[simonw]

New documentation:

• https://sqlite-utils.datasette.io/en/latest/python-api.html#detecting-column-types-using-typetracker
• https://sqlite-utils.datasette.io/en/latest/reference.html#sqlite-utils-utils-typetracker