Python 2 vs Python 3 - Difference in Filter Behavior

Question

Can someone please help me understand why the following code that implements the "Eratosthenes sieve" behaves differently in Python 2 and Python 3.

l = range(2, 20)
for i in range(2, 6):
    l = filter(lambda x: x == i or x % i != 0, l)
print(tuple(l))

As of Python 2.7:

> python filter.py
(2, 3, 5, 7, 11, 13, 17, 19)

since Python 3.6:

> python filter.py
(2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 16, 17, 18, 19)

I understand that the Python3 filter returns a filter object, but cannot explain the final result. (The code from this tutorial is lambdas 1 ).

Answer 1

There are two roles here:

• in python-3.x , filterworks as a generator: filtering is done lazily; and
• updated iin lambda x : ..., and also iin the loop formakes a progression.

, , , - :

l = filter(lambda x: x == 5 or x % 5 != 0,
        filter(lambda x: x == 5 or x % 5 != 0,
            filter(lambda x: x == 5 or x % 5 != 0,
                filter(lambda x: x == 5 or x % 5 != 0,l)
            )
        )
    )

, , i 5 . , tuple(..), , , , , .

list , filter ing:

l = range(2, 20)
for i in range(2, 6):
    l = list(filter(lambda x: x == i or x % i != 0, l))
print(tuple(l))

python :

>>> l = range(2, 20)
>>> for i in range(2, 6):
...     l = list(filter(lambda x: x == i or x % i != 0, l))
... 
>>> print(l)
[2, 3, 5, 7, 11, 13, 17, 19]

, python-2.7 python-3.x , "" , : , , .

( @ShadowRanger) , i . , " ". :

lambda x : x == i or x % i != 0

:

(lambda j : (lambda x : x == j or x % j != 0))(i)

, , j, i. , j i.

Answer 2

Python-3 filter ( Python-2 ), , . , , i . , filter i = 5 filter, .

print -, , :

l = range(2, 20)
for i in range(2, 6):
    l = filter(lambda x: print(x, i) or (x == i or x % i != 0), l)
list(l)

2 5
2 5
2 5
2 5
3 5
3 5
3 5
3 5
4 5
4 5
4 5
4 5
5 5
5 5
5 5
5 5
6 5
6 5
6 5
6 5
7 5
7 5
7 5
7 5
8 5
8 5
8 5
8 5
9 5
9 5
9 5
9 5
10 5
11 5
11 5
11 5
11 5
12 5
12 5
12 5
12 5
13 5
13 5
13 5
13 5
14 5
14 5
14 5
14 5
15 5
16 5
16 5
16 5
16 5
17 5
17 5
17 5
17 5
18 5
18 5
18 5
18 5
19 5
19 5
19 5
19 5

[2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 16, 17, 18, 19]

, , . i :

l = range(2, 20)
for i in range(2, 6):
    l = filter((lambda j: lambda x: print(x, j) or (x == j or x % j != 0))(i), l)
    # or
    # l = filter(lambda x, i=i: print(x, i) or (x == i or x % i != 0), l)
list(l)
2 2
2 3
2 4
2 5
3 2
3 3
3 4
3 5
4 2
5 2
5 3
5 4
5 5
6 2
7 2
7 3
7 4
7 5
8 2
9 2
9 3
10 2
11 2
11 3
11 4
11 5
12 2
13 2
13 3
13 4
13 5
14 2
15 2
15 3
16 2
17 2
17 3
17 4
17 5
18 2
19 2
19 3
19 4
19 5

[2, 3, 5, 7, 11, 13, 17, 19]

filter - tuple:

l = range(2, 20)
for i in range(2, 6):
    l = tuple(filter(lambda x: x == i or x % i != 0, l))
print(l)
# (2, 3, 5, 7, 11, 13, 17, 19)