🔒 mypy gives me an error which I dont know how to fix

[mint jacinth]

def make_chapters() -> None:
    """Create all dirs."""
    delete_chapters()
    [os.mkdir(f'Chapter {i}') for i in range(1, 9 + 1)]

"mkdir" does not return a value (it only ever returns None)

[sonic harness]

@mint jacinth

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[mint jacinth]

I might just write

for i in range(1, 9 + 1):
  os.mkdir(f'Chapter {i}') 

But I want this to be done by using 1 line

And I still dont get why mypy gives me this error, since I have () -> None:

[broken flume]

U can use map

To do it in 1 line

!map

[sonic harness]

Did you mean...

» mutable-default-args
» if-name-main

[broken flume]

!doc map

[sonic harness]

map

map(function, iterable, *iterables)```
Return an iterator that applies *function* to every item of *iterable*, yielding the results. If additional *iterables* arguments are passed, *function* must take that many arguments and is applied to the items from all iterables in parallel. With multiple iterables, the iterator stops when the shortest iterable is exhausted. For cases where the function inputs are already arranged into argument tuples, see [`itertools.starmap()`](https://docs.python.org/3/library/itertools.html#itertools.starmap).

Similar names: 2to3fixer.map

[broken flume]

like map(lambda i: os.mkdir(f'Chapter {i}'), range(1, 9 + 1))

I’m on mobile so I can’t really check

I think that works bc it maps those inputs to the lambda function

That technically doesn’t evaluate it tho

list(map(lambda i: os.mkdir(f'Chapter {i}'), range(1, 9 + 1)))

will make them all evaluate

[tight mantle]

you can just write it as 1 line then:

for i in range(1, 9 + 1): os.mkdir(f'Chapter {i}')```
the line break is optional, but every statement within the block has to be on that line, and it cannot have blocks within

[broken flume]

map(os.mkdir, [f'Chapter {i}' for i in range(1, 9 + 1)]))

Pr sure this works too

[mint jacinth]

flake8 E902 :)

Oh no

Thats about another line, let me check again

Surprisingly linter doesnt give me any error about that, thx for that. Anyway want to try write this by map

[tight mantle]

map is a lazy iterable, so for it to do anything you have to wrap it in a call to something like list, as done here

[broken flume]

yeah theoretically slightly less useful to use map when you don’t care about the data

Because it forces you to return the values vs in a for loop u can just ignore them

But in big functions it’s usually more efficient than a for loop if you are trying to generate a huge list from passing values into a function

[tight mantle]

suppose you tried a list comprehension again, but placed the mkdir calls in the condition:

[0 for i in range(1, 9+1) if os.mkdir(f'Chapter {i}')]```
would it give you another IDE error?

[mint jacinth]

I'm currently in Beijing, VPN doesn't work correctly, so we have some delays in response, sorry

[mint jacinth]

I got the same mypy error

error: "mkdir" does not return a value (it only ever returns None) [func-returns-value]

I think for i in range(1, 9 + 1): os.mkdir(f'Chapter {i}') is the best solution here. Make it simple, isnt it?

Thank you for help @broken flume @tight mantle 😎

!close

[sonic harness]

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