If Else in List Comprehension, Python

In a python List Comprehension, the usual style of using an if statement is as below:

["Even" for el in range(1,7) if el%2 == 0]

which goves you the output:
[‘Even’, ‘Even’, ‘Even’]

But if we want to add an else clause to the above list the most intuitive way is to just add the else clause at the end as below:

["Even" for el in range(1,7) if el%2 == 0 else "Odd"]

If you try to run the above code python throws an error, so we need to use a conditional expression which is not part of the list comprehension syntax.

The correct way to do this is as follows:

["Even" if el%2 == 0 else "Odd" for el in range(1,7)]

which gives the output:
[‘Odd’, ‘Even’, ‘Odd’, ‘Even’, ‘Odd’, ‘Even’]

Multiple if else conditionals can be used in a list comprehension. But the ternary form of the conditionals does not have an elif construct but it can be simulated using the else condition as follows:

["Even" if el%2==0 else "divby3" if el%3==0 else "divby5" if el%5==0 else "None" for el in range(1,15)]

This is exactly like saying:

for v in l:
    if v == 1 :
        print 'yes'
    else:
        if v == 2:
            print 'no'
        else:
            print 'idle'

which gives the output:
[‘None’, ‘Even’, ‘divby3’, ‘Even’, ‘divby5’, ‘Even’, ‘None’, ‘Even’, ‘divby3’, ‘Even’, ‘None’, ‘Even’, ‘None’, ‘Even’]

We can also frame more than one for loop in the form of a list comprehension. Let’s take the the following piece of code which has two for loops.

arr = [10,8,7,14,5]

for i in range(0,len(arr)):
        for j in range(0,i):
            if arr[j] < arr[i]:
                print(arr[i]-arr[j])

The same piece of code in list comprehension is as follows:

[arr[i]-arr[j] for i in range(0,len(arr)) for j in range(0,i) if (arr[j] < arr[i])]