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• Python+Deep+Dive+2.pdf

• List Comprehension

  • nested

  [(i, j) for i in range(1, 6) if i%2==0 for j in range(1, 6) if j%3==0]
  [[i*j for j in range(5)] for i in range 5]
  

  - Generator - something that yield is a generator - List comprehension build with [], generator expression build with () - (i**2 for i in range(5)) - Lazy evaluation and local scope . get value of i**2 until next - yield and yield from (python 3.3) - yield is used to produce a value from the generator and to suspend the function’s state so that it can be resumed right from where it left off. - It essentially allows the function to return a value (like a regular function would with return) but remembers its state for future calls.

    ``` python
    def simple_generator():
        yield 1
        yield 2
        yield 3
  
    gen = simple_generator()
  
    print(next(gen))  # Output: 1
    print(next(gen))  # Output: 2
    print(next(gen))  # Output: 3
    ```
  - `yield from` is used to delegate part of its operations to another generator. This simplifies the code when a generator function is calling another generator function. It's a way to yield all values from another iterable (often another generator) without using a loop.
  - Example:
  
    ``` python
    def generator_without_yield_from():
        for item in simple_generator():
            yield item
  
    gen = generator_without_yield_from()
  
    print(next(gen))  # Output: 1
    print(next(gen))  # Output: 2
    print(next(gen))  # Output: 3
  
    # with yield from
    def generator_with_yield_from():
        yield from simple_generator()
  
    gen = generator_with_yield_from()
  
    print(next(gen))  # Output: 1
    print(next(gen))  # Output: 2
    print(next(gen))  # Output: 3
    ```
  - User case
      - `yield`: When you're producing values in a generator function.
      - `yield from`: When you want to delegate yielding values to another generator (or any iterable) within a generator function.
      - also `yield from` is useful when `with open(filename) as f:` context and you should `yield from` instead of `yield` or `return` the lazy iterator inside context
  

  • Set
  • operations
    • | : union, set1|set2|set3
    • &: join set1 & set2 & set3
    • -: difference set1 - set2
    • ^: semmetric difference, same as (s1 | s2) -( s1 & s2 )
    • < and <= containment, > and >=
  • mutate a set

    - |=, &=, -=, ^=

  • frozenset is a const set