CODEWITHSUNDEEP
pythonlistpython-2.x
Mock
Mock

Reputation: 379

Appending a range to a list

I have some basic code that I'm not grasping the behaviour of:

L = [ 'a', 'bb', 'ccc' ]

L.append(range(2))
print len(L)

print len(L + range(1))

print len(L)

The output of which is 

4
5
4

This is confusing to me, as my thought process is that the length of the initial list is 3, and appending range(2) to the end brings it to length of 5. Therefore I'd expect the output to be 5 6 5. I'm sure it's a simple quirk, but I'm a bit lost and having a hell of a time trying to find an answer online. Would anyone be able to point me in the right direction?

Upvotes: 14

Views: 59250

Answers (2)

Don Feto
Don Feto

Reputation: 1486

Insert A Range of item or to List anywhere

 g=[1,2,3,4,7,8]        
    z=[5,6]
    def insertRange(start,YourList,anotherlist):
        if isinstance(YourList,list) and isinstance(anotherlist,list) :
            YourlistPart1=YourList[0:start]
            YourlistPart2=YourList[start:]
            YourlistPart1.extend(anotherlist)
            YourlistPart1.extend(YourlistPart2)
            print(YourlistPart1)
    
    insertRange(4,g,z)

You can't insert range in a specific location in python but you can work around by function using extend you can split your list extend first part and then merge the 2 lists again start= doesn't start from 0 if you wish to start insert from index 3 which = 4 in the example you start with 3

summary

start from 1 adds the list after the index 0 and shift the other elements

start from 4 adds the list after the index 3 and shift the other elements

start from 5 adds the list after the index 4

Upvotes: 0

Martijn Pieters
Martijn Pieters

Reputation: 1121416

You appended a single list object. You did not add the elements from the list that range produces to L. A nested list object adds just one more element:

>>> L = ['a', 'bb', 'ccc']
>>> L.append(range(2))
>>> L
['a', 'bb', 'ccc', [0, 1]]

Note the [0, 1], the output of the range() function.

You are looking for list.extend() instead:

>>> L = ['a', 'bb', 'ccc']
>>> L.extend(range(2))
>>> L
['a', 'bb', 'ccc', 0, 1]
>>> len(L)
5

As an alternative to list.extend(), in most circumstances you can use += augmented assignment too (but take into account the updated L list is assigned back to L, which can lead to surprises when L was a class attribute):

>>> L = ['a', 'bb', 'ccc']
>>> L += range(2)
>>> L
['a', 'bb', 'ccc', 0, 1]

Upvotes: 28

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