Inserting a string into a list only using the append method

Question

I'm struggling with a question at the moment and was wondering if someone could point out and show me where I'm going wrong. I need to insert a string into a list only using the append method at a designated position specified by an insert_position. Here is my code:

str1_list = ['one', 'three', 'four']

def insert_value(my_list, value, insert_position):

       new_list = []
       for i in range(len(my_list)):
             if i < insert_position:
                 new_list.append(my_list[i])
             elif i == insert_position:
                 new_list.append(my_list[i])
             else:
                 new_list.append(my_list[i-1])

       return new_list

print(str1_list, 'two', 1)

Output should be:

['one', 'two', 'three', 'four']

I know the value parameter needs to be somewhere but can't figure out where. Any help will be greatly appreciated.

Thanks

Have you tried stepping through the code manually? Also, consider: how many times do you expect the loop to run, and how many times does .append need to be called on new_list? — Karl Knechtel
– Karl Knechtel, Commented Nov 11, 2019 at 10:29
Do you really need to use the .append method ? Anything else is accepted ? no methods in view at all ? — han solo
– han solo, Commented Nov 11, 2019 at 10:45

Aryerez · Accepted Answer · 2019-11-11 10:38:12Z

2

You have a few errors (not using the value passed to the function, not caling the function, unneccesary condition). Compare you code with this:

str1_list = ['one', 'three', 'four']
def insert_value(my_list, value, insert_position):
    new_list = []
    for i in range(len(my_list)):
        if i == insert_position:
            new_list.append(value)
        new_list.append(my_list[i])
    return new_list
print(insert_value(str1_list, 'two', 1))

Output:

['one', 'two', 'three', 'four']

edited Nov 11, 2019 at 10:38

answered Nov 11, 2019 at 10:33

Aryerez

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1 Comment

zeps Over a year ago

I see where I have gone wrong. I needed to first append the value and then insert it at the index of i. Thanks

han solo · Accepted Answer · 2019-11-11 10:53:49Z

2

You could just add the new value with the slice like,

>>> def insert_value(l, value, pos):
...     l[pos:pos] = [value]
...     return l # return is not required, since you want to modify the list ?
... 
>>> l = ['one', 'three', 'four']
>>> insert_value(l, 'two', 1)
['one', 'two', 'three', 'four']
>>> l
['one', 'two', 'three', 'four']

edited Nov 11, 2019 at 10:53

answered Nov 11, 2019 at 10:48

han solo

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