eolas/_meta/Unsorted_notes.md

Difference in import types Python

import x requires dot notation to individuate different components in the module

from x import y

import a component directly from the module removes the need to use dot notation to indviduate

Complex filter function using lambdas

def update_entries(old, new):
    """Merge old and new data, removing dupes"""
    combined = old + new
    seen = set()

    filter_func = lambda x: not (tuple(x) in seen or seen.add(tuple(x)))

    unique_combined = list(filter(filter_func, combined))

ChatGpt explanation

Certainly, the line

filter_func = lambda x: not (tuple(x) in seen or seen.add(tuple(x)))

creates a lambda function that takes a single argument x, where x is expected to be a list. The function converts x to a tuple and checks for its existence in the seen set.

Here is a breakdown of the logic:

1. tuple(x): This converts the list x to a tuple because lists are unhashable and cannot be stored in a set. Tuples, being immutable, can be stored in a set.

2. tuple(x) in seen: This checks whether the tuple form of x is already in the seen set.

3. seen.add(tuple(x)): This adds the tuple form of x to the seen set. The add method of a set returns None.

4. tuple(x) in seen or seen.add(tuple(x)): This combines the above two steps. The or operator returns the first "truthy" value it encounters, or the last value otherwise. Since seen.add() returns None, which is "falsy," this part will return True if tuple(x) was already in seen, and None otherwise. Importantly, if tuple(x) was not already in seen, it will be added.

5. not (...): The not negates the result. So if tuple(x) in seen was True, not True would be False, causing the filter to skip this item. If tuple(x) in seen was False, not None would be True, causing the filter to include this item and also adding it to seen.

In summary, the lambda function acts as a filter that only returns True for the first occurrence of each unique list x, after converting it to a tuple for hashability and set membership tests. After a unique list has been seen once, any subsequent occurrences will cause the lambda function to return False, effectively filtering them out.