Python: Adding element to list while iterating

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I know that it is not allowed to remove elements while iterating a list, but is it allowed to add elements to a python list while iterating. Here is an example:

    for a in myarr:
      if somecond(a):
          myarr.append(newObj())

I have tried this in my code and it seems to work fine, however I don't know if it's because I am just lucky and that it will break at some point in the future?

EDIT: I prefer not to copy the list since "myarr" is huge, and therefore it would be too slow. Also I need to check the appended objects with "somecond()".

EDIT: At some point "somecond(a)" will be false, so there can not be an infinite loop.

EDIT: Someone asked about the "somecond()" function. Each object in myarr has a size, and each time "somecond(a)" is true and a new object is appended to the list, the new object will have a size smaller than a. "somecond()" has an epsilon for how small objects can be and if they are too small it will return "false"

iteration python
12 Answers

Assuming you are adding at the last of this list arr, You can try this method I often use,

arr = [...The list I want to work with]
current_length = len(arr)
i = 0
while i < current_length:
    current_element = arr[i]
    do_something(arr[i])
    # Time to insert
    insert_count = 1 # How many Items you are adding add the last
    arr.append(item_to_be inserted)
    # IMPORTANT!!!!  increase the current limit and indexer
    i += 1
    current_length += insert_count

This is just boilerplate and if you run this, your program will freeze because of infinite loop. DO NOT FORGET TO TERMINATE THE LOOP unless you need so.

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