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Python Python Collections (2016, retired 2019) Slices Introduction To Slices

Sohail Mirza
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Sohail Mirza
Python Web Development Techdegree Student 5,158 Points
Posted by Sohail Mirza
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Sohail Mirza
Python Web Development Techdegree Student 5,158 Points

using [:]

Sorry my question is very weird. In this video towards the end Kenneth use the following code clean_list = messy_list[:] , my question is why wouldnt the following line work clean_list = messy_list , all i am doing is removing is [:]

I understand kenneth said it copy all contents but again why wouldnt it work just by omitting [:]

why wouldnt this work

1 Answer

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

When you make an assignment using a list, the assigned variable becomes a reference to the same list. If you want a copy of the list instead, you must make one with an operation like a slice or using the ".copy()" method.

If you make any changes to the original list, the difference between a reference and a copy will become significant. For example:

test = [1, 2]
test_ref = test
test_cpy = test[:]
test[0] = 99
print(test_ref[0])  # will show "99"
print(test_cpy[0])  # will show "1"