Generating a list of EVEN numbers in Python

Question

Basically I need help in generating even numbers from a list that I have created in Python:

[1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597         


        

Answer 1

You could use a for and if loop using the length function, like this:

for x in range(len(numList)):
    if x%2 == 0:
        print(x)
        NewList.append(x)

Answer 2

Basically you should create a variable and put your list in and then sort your even numbers list by adding it only the even numbers

numbers = [1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 28657, 46368, ...] even = [e for e in numbers if e%2==0]

Answer 3

Just for fun, checking if number%2 != 1 also works ;)

evens=[x for x in evens_and_odds if number%2 != 1 ]

Note that you can do some clever things to separate out evens and odds in one loop:

evens=[]
odds=[]
numbers=[ evens, odds ]
for x in evens_and_odds:
    numbers[x%2 == 1].append(x)

print evens
print odds   

The above trick works because logical expressions (==, >, etc.) operating on numbers True (1) and/or False (0).

Answer 4

You can do this with a list comprehension:

evens = [n for n in numbers if n % 2 == 0]

You can also use the filter function.

evens = filter(lambda x: x % 2 == 0,numbers)

If the list is very long it may be desirable to create something to iterate over the list rather than create a copy of half of it using ifilter from itertools:

from itertools import ifilter
evens = ifilter(lambda x: x % 2 == 0,numbers)

Or by using a generator expression:

evens = (n for n in numbers if n % 2 == 0)

Answer 5

Use a list comprehension (see: Searching a list of objects in Python)

myList = [<your list>]
evensList = [x for x in myList if x % 2 == 0]

This is good because it leaves list intact, and you can work with evensList as a normal list object.

Hope this helps!

Answer 6

In your specific case my_list[1::3] will work. There are always two odd integers between even integers in fibonacci: even, odd, odd, even, odd, odd.....

>>> my_list = [1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 28657, 46368]
>>>         
... 
>>> my_list[1::3]
[2, 8, 34, 144, 610, 2584, 10946, 46368]