How to return the length of each element in a list using the Len() function?

Question

The problem:

Write a loop that traverses:

['spam!', 1, ['Brie', 'Roquefort', 'Pol le Veq'], [1, 2, 3]]

and prints the length of each element.

I have tried as my solution:

list = ['spam!', 1,['Brie', 'Roquefort', 'Pol le Veq'], [1,2,3]]
element = 0

for i in list:
    print len(list[element])
    element += 1

But it receives this error: TypeError: object of type 'int' has no len()

Answer 1

As others have pointed out, the number 1 (second entry of the main list) does not have a defined length. But you still can catch the exception and print out something if something like this is the case, e.g.

myList = ['spam!', 1,['Brie', 'Roquefort', 'Pol le Veq'], [1,2,3]]

for entry in myList:
    try:
        l = len(entry)
        print "Length of", entry, "is", l
    except:
        print "Element", entry, "has no defined length"

Answer 2

First of all, using that element variable as an index for accessing your list items is redundant. When writing a for loop in python, you are iterating through each item in the list such that, on iteration 1:

for item in [1, [1,2,3]]:
    # item = 1
    ...

And on the next iteration: for item in [1, [1,2,3]]: # item = [1, 2, 3] ...

The next problem is that you have an item in that list with no defined length. I don't know what you want to do with that, but a possible solution is this, which will print the length of the item (in digits) if the item is an integer:

items = ['spam!', 1,['Brie', 'Roquefort', 'Pol le Veq'], [1,2,3]]

for item in items:
    if isinstance(item, int):
        print(len(str(item)))
    else:
        print(len(item))

Answer 3

I was thinking on your question and I thought that you maybe were new in Python as me, for me everything was solved in R. The solution that I found is to set all the elements in the list... into a list 'element' so the last code can run over all the lists in the list:

for k in range(len(items)):
    if type(items[k])!= list:
       items[k]=[items[k]]
items

[len(i) for i in items]
>>[1, 1, 3, 3]

Answer 4

The only possible solution is change the int type to str and vice-versa. If it is only a exercise, it should be not a problem.

Answer 5

Can use map and __ len __ to check does it will raise error when use len(), e.g.

myList = ['spam!', 1,['Brie', 'Roquefort', 'Pol le Veq'], [1,2,3]]
myList_filter = list(filter(lambda x: hasattr(x, "__len__"), myList))
myList_len = list(map(len, myList_filter)) 
print(myList_len) # [5, 1, 3, 3]

error_type = [entry for entry in myList if entry not in myList_filter]
print("{0} has no defined length".format(error_type)) # [1] has no defined length

Answer 6

def listlen(lists1):

    """
    return length of each element in a list     
    """
    import numpy
    newlist = []
    for item in lists1:
        if type(item) in [list,str,numpy.ndarray]:
            newlist.append(len(item))
        else:
            newlist.append(len([item]))
    return newlist

# example usage -
listlen(["somestring", 5, [1,2,3]] )

[10, 1, 3]