Let me tell you why it is always 100% unnecessary to use a full slice [:] with a string in Python.

Full slice of a string is irrelevant

Yesterday I challenged your Python 🐍 knowledge!

I asked:

Why is it always 100% unnecessary to use a full slice [:] with a string?

Now it's time I give you the answer!

Let's go 🚀

my_str = "Hello, world!"
#     vvv never use this with strings.
my_str[:]

Recall that slices do a copy of the sliced chunk.

If you are using a full slice my_str[:], that means you are getting the whole string.

So, why wouldn't you just use my_str..?

Why do you need a copy of your string?

Sometimes you do need a copy of a list:

>>> words = "How is your day going?".split()
>>> words
['How', 'is', 'your', 'day', 'going?']
>>> their_words = words[:]
>>> their_words[2] = "their"
>>> their_words
['How', 'is', 'their', 'day', 'going?']
# changed     ^^^^^^^
>>> words
['How', 'is', 'your', 'day', 'going?']
# original    ^^^^^^

Sometimes you need a copy of a list because lists are mutable.

This means that the contents of a list can change!

So, if you want to modify a list but also keep its original values, you need a copy.

But this doesn't make sense for strings!

Can you see why?

>>> l = [42, 73, 0, 10]
>>> new_l = l  # Regular assignment...
>>> new_l[1] = 999
>>> l
[42, 999, 0, 10]
#    ^^^ valued changed “through” new_l.

It doesn't make sense to get a copy of a string because strings are immutable!

What does this mean?

It means that the contents of a string never change!

For example, haven't you noticed how .upper returns a new string?

You never modify the original string!

>>> hey = "Hey!"
>>> scream = hey.upper()
# All upper case:
>>> scream
'HEY!'
# Preserved its casing:
>>> hey
'Hey!'

That is why it never makes sense to make a copy of a string.

You can't change it either way, so might as well use the original string from the start!

Did this make sense?

I hope so 🤞

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Key takeaways:

• [:] copies sliced object
• lists are mutable, i.e., their contents can change
• useful, for example, when you want to modify a list & also keep the original
• irrelevant for strings because strings are immutable, i.e., their contents can't change

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