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sorted function example mystery
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sorted function example mystery
The following code works, but I don't know why (I'm using python v 3.7.3)

print(f'{"".join(sorted("foo", key="of".index))}')
It correctly prints oof

I don't understand:
"of".index is the index function of str.
It return the index of an element. The function takes an element, which must be inside the str.
If not, it will raise a ValueError.

The key function is called for each char in the str (str is iterable).
The sort order is defined as follows: o == 0 and f == 1
This means, that after sorting, the o comes first, then the f.

It's a strange way to get a custom defined sorting order for str.
My code examples are always for Python >=3.6.0
Almost dead, but too lazy to die:
All humans together. We don't need politicians!
To illustrate DeaD_Eye answer with code:

>>> 'of'.index('f')
>>> 'of'.index('o')
>>> 'of'.index('a')
ValueError: substring not found
I'm not 'in'-sane. Indeed, I am so far 'out' of sane that you appear a tiny blip on the distant coast of sanity. Bucky Katt, Get Fuzzy

Da Bishop: There's a dead bishop on the landing. I don't know who keeps bringing them in here. ....but society is to blame.
Thanks guys. I'm studying Python by working through coding problems from
It's a good site as there are many code examples of the same problem to look at.
This example snippet you've posted is an Anti-pattern.
The sense behind f-strings are to make it easier readable and not to save lines of code.

def my_keyfunc(char):
    Return the index of the string "of"
    return "of".index(char)

sorted_str = "".join(sorted("foo", key=my_keyfunc))
print(f'This is the sorted_str: {sorted_str}')
My code examples are always for Python >=3.6.0
Almost dead, but too lazy to die:
All humans together. We don't need politicians!

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