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Python Python Collections (2016, retired 2019) Lists Removing items from a list

Posted by akshaan Mazumdar
akshaan Mazumdar
997 Points

Is there a way to check the data types in a loop ?

I can use del and remove the string and list and boolean one by one. But is there a way i could run the list through a loop and check the items for their data type????

lists.py 
messy_list = ["a", 2, 3, 1, False, [1, 2, 3]]

# Your code goes below here
X=messy_list.pop(3)
messy_list.insert(0,X)

2 Answers

codeoverload
codeoverload
24,260 Points
codeoverload
codeoverload
24,260 Points

This is how I would do it:

messy_list = ["a", 2, 3, 1, False, [1, 2, 3]]

# Your code goes below here
messy_list.insert(0, messy_list.pop(messy_list.index(1)))
copy_list = messy_list[:] # Make a copy of messy_list
for item in copy_list: # Iterate over copy_list
    if type(item) is not int: 
        del messy_list[messy_list.index(item)] # if the item isn't an int remove it from messy_list

You need to make a copy of messy_list because you can't remove items from a list while iterating over it.

If you've still got questions, don't hesitate to ask me :)

Daniel Santos
Daniel Santos
34,969 Points

I wouldn't make a copy. If the list is huge, then your program will not perform well. Here is what I would do:

messy_list = ["a", 2, 3, 1, False, [1, 2, 3]]

clean_list = []

for item in messy_list:
    if type(item) is int:
        clean_list.append(item)

print(clean_list)

Check my official answer, which is another way of doing this.

codeoverload
codeoverload
24,260 Points
codeoverload
codeoverload
24,260 Points

From a performance perspective you're certainly right :)
I just wanted to modify the messy_list directly because of the code challenge.
But still thanks for your suggestion!

Daniel Santos
Daniel Santos
34,969 Points
Daniel Santos
Daniel Santos
34,969 Points

This is a functional way of solving this problem. It doesn't require explicit copy of the list and its just one line. Of course, don't give up readability for less code. I just wanted to show another way of doing it and if it makes sense for you, even better.

messy_list = ["a", 2, 3, 1, False, [1, 2, 3]]

# filter will iterate through every element in messy_list, and you can access them with x.
# If type(x) is int evaluates to True, then whatever element x is a the moment will be included
# in the new list.
clean_list = list(filter(lambda x: type(x) is int, messy_list))

print(clean_list)

This is a more functional programming style, if you have any questions, please let me know.

-Dan