[Python] Comprehension notation. Write a for statement simply. (A collection is the difference between an iterator and an iterator)

[Python] Comprehension notation. Write a for statement simply. (A collection is the difference between an iterator and an iterator)

You can create a list, set type, etc. (collection) using a for statement.

What is a comprehension?

How to write a for statement easily.

・ [Expression for variable in iterable] └ If you enclose it in [], the output type will be list. └ {} is a set type

[(i*2) for i in range(5)]

#output
[0, 2, 4, 6, 8]

The output is in list format. Same as below.

python

arrs=[]
for i in range(5):
    arr = (i*2)
    arrs.append(arr)
arrs

#output
[0, 2, 4, 6, 8]

▼ {} is a set type

{(i*2) for i in range(5)}

#output
{0, 2, 4, 6, 8}

list, range, set, etc.

Str, int, float, etc. that can only have one data are not collections.

■ Difference between iterator and iterator

Iterable is a general term for repeatable objects. Iterators are a type of iterator and are more limited.

** ・ Iterable ** A repeatable object. Objects of type list, tapple, range.

"For i in iterable"

** ▼ Confirmation of iterator type **

For list

arr = [1,2,3,4,5]

iterArr = iter(arr)
type(iterArr)

#list_iterator

For tuple

brr = (1,2,3,4,5)

iterArr = iter(arr)
type(iterArr)

#tuple_iterator

For range

crr = range(5)

iterArr = iter(arr)
type(iterArr)

#range_iterator

** ・ next function ** Extract the elements of type iter one by one. irreversible.

next (iterator)

Iterator & next

arr = [1,2,3,4,5]
iterArr = iter(arr)

next(iterArr)
1

next(iterArr)
2
~
~
~
next(iterArr)
5

next(iterArr)
StopIteration: #← An error will occur if all are extracted

If you use an iterator and next, you can process in order.

▼ Iterators can also use for statements. Iterators are one of the iterator elements.

python

arr = [1,2,3]
iterArr = iter(arr)

for i in iterArr:
    print(i)

1
2
3