Join, set set, dark copy in Python

A. Join
1. The join method in Str. Convert a list to a string
2. Lists and dictionaries cannot be deleted directly in the loop.
You need to record the content you want to delete in the new list.
The new list is then recycled. Delete a dictionary or list
3. Fromkeys ()
1. Return to the new dictionary. No effect on the original dictionary
2. The following value. Is multiple keys share a value
Two. Set Set
Features: unordered, non-repeating, elements must be hashed (immutable)
Function: To repeat
itself is a mutable data type. There is an increase and deletion check operation.
Frozenset () freezes the collection. Immutable. Hash-able
Three. Depth copy (difficulty)
1. Assign a value. No new objects were created. Common same Object
2. Shallow copy. Copy the first layer of content. [:] or copy ()
3. Deep copy. Copy all content. including all the inside.

Join, set set, dark copy in Python