Advantages and disadvantages of generator and list derivation in Python3 __python

The difference between a list derivation and a generator in Python3:

(1)

The list derivation is to load all the values into memory at once

The builder converts a list-inferred [] to (), does not load all values into memory at once, delays the calculation, returns one result at a time, and it does not produce all the results at once, which is useful for processing large amounts of data.

Fun ():
    Range (1,50): Sleep
        (1)
        i

Fun ():
    print ( I

# generator Function: A function contains the yield key, then this function is not a normal function, is a generator function
# call the generator function, not immediately execute the code inside the function, but will return a generator

Func ():
    print ("a")
    yield
    print ("B")
    yield
 Print ("C")     
    yield
 Print ("D")     
    yield

Generator = func ()
print (generator)
print (Type (generator))

# Next (Generator)
# next (Generator)
# Next (Generator)
Generator: Pass 
    

Range (10000000000))
Range (10000000000)])

The first one has almost no memory footprint, and the second memory occupies a lot

Principle: The built-in function in Python3 when the SUM function uses the iterator protocol to access the object, and the generator implements the iterator protocol, so we can directly compute the sum of a series of values without having to construct a list first.

The builder can also improve the readability of your code:

# for a paragraph of text, where
 each word appears index_words (text): Result
    = []
    text:
        result.append (0)
     Enumerate (text,1): ": Result.append ( 
        
            index)
     Result

index_words (text):
    text:
        0
      Enumerate (text,1):
        ':
            Index

(2)

List derivations can traverse any of the Times

The builder can only traverse once

Range (1,5)) print
(next generator) print (
next (generator)
) Generator:
    Print (i
)generator:
    print (i)

Print results:

1
2
3
4

Range (1,5)]
print (list1[0])
print (list1[1])
print (list1[2)
list1:
    print (i)
 list1: Print ( 
    i)

Print results:

1
2
3
1
2
3
4
1
2
3
4