Python String Of Letters Is A String Of Letters, But Not With Special
Waylon Walker
Learning in Public @_WaylonWalker
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In python, a string is a string until you add special characters.
In browsing twitter this morning I came accross this tweet, that showed that
you can use is accross two strings if they do not contain special characters.
https://twitter.com/bascodes/status/1492147596688871424
I popped open ipython to play with this. I could confirm on 3.9.7, short
strings that I typed in worked as expected.
waylonwalker ↪main v3.9.7 ipython ❯ a = "asdf" waylonwalker ↪main v3.9.7 ipython ❯ b = "asdf" waylonwalker ↪main v3.9.7 ipython ❯ a is b True
Using the upper() method on these strings does break down.
waylonwalker ↪main v3.9.7 ipython ❯ a.upper() is b.upper() False waylonwalker ↪main v3.9.7 ipython ❯ a = "ASDF" waylonwalker ↪main v3.9.7 ipython ❯ b = "ASDF" waylonwalker ↪main v3.9.7 ipython ❯ a is b True
If You can also see this in the id of the objects as well, which is the memmory address in CPython.
waylonwalker ↪main v3.9.7 ipython ❯ id(a) 140717359289568 waylonwalker ↪main v3.9.7 ipython ❯ id(b) 140717359289568 waylonwalker ↪main v3.9.7 ipython ❯ id(a.upper()) 140717359581824 waylonwalker ↪main v3.9.7 ipython ❯ id(b.upper()) 140717360337824
Finally just as the post shows if you add a special character in there it also breaks.
waylonwalker ↪main v3.9.7 ipython ❯ a = "ASDF!" waylonwalker ↪main v3.9.7 ipython ❯ b = "ASDF!" waylonwalker ↪main v3.9.7 ipython ❯ a is b False
What should you do
First and foremost, these are the exact pitfalls that flake8 guards you
against. So the very first things you should take away here is that there is a
lot of wisdom and value in flake8.
Second, the is comparison should be used for things that you want to compare
to exact memmory addresses. These include booleans and None. Don't use is
accross two assigned variables.