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So what if you need to work with
Python versions before 3.5 and

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you still wanna use types.

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Or maybe you don't want to stub
your entire library of code,

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you don't wanna hint everything,
just a file or two at a time.

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But you wanna make sure they don't look
weird to the other developers on your team

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or other teams at your company, or
maybe you want to specify types for

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someone else's library, but they're
resisting poor requests for type hints.

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This is where a very handy feature
known as stub files comes in.

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If you're familiar with C# typescript,
or Collin, this may look very similar.

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So to start off we're gonna create
a new file in typing workshop.

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That is called calculator.pyi.

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So this is the stub file.

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Stub files in Python always
have a .pyi extension and

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they have to share the module name
with the module they define types for.

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So calculator.py, calculator.pyi.

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ingredient.py, ingredient.pyi and so on.

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There are ways to change
the location of the PYI files.

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If you check the my pie docs.

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If you need that then
you'll see how to do it.

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I've put a link in the teacher's notes.

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Now in calculator.pyi, I basically
just redefined my functions and types.

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In fact, I'm actually just going
to copy and paste them over.

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So copy all that, paste it into here.

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But a PYI file doesn't actually
need to have any logic or

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anything like that in it.

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So I'm gonna remove
the body of the functions.

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I'm gonna remove move down here
where I called the print method.

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And I'm gonna remove the colons from
the ends of the function definitions.

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Because we don't need those either,

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because we're not actually
defining functions.

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So, all we're saying is,
hey there's a function here named add and

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it takes these two numbers that are reals.

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In fact, let's go ahead and
change this to real.

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There we go, okay.

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Now that I have the stub file defined,

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I can remove all of the type
hinting from calculator.pyi.

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So I don't need this
from numbers import real.

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And I don't need any of this stuff, so
give me a second while I clean it up.

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And so now if you look, you notice
that I still have the warning for

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using the string when it
expected a type real.

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And if you're in py charm you'll
see these little stars here

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that have a stub item and if I click on
those I'm taken directly to the stub.

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Now if you're using Python 2.7 or
2.3 or whatever.

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You'll never know that these type hints
are there, that they're available.

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So you don't have to worry about
confusing other members of your team or

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other people who use a project
with these type hints.

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If you wanna use type hints but
you don't use py charm.

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You can use the my pypackage
to check your types.

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Type hints add a great safety net to
Python code bases, especially large ones.

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I know that every project
no matter how big or

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small needs more documentation
than it actually has.

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While hints won't replace documentation,
they can definitely reduce the number of

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times you or a coworker has to
dive into the source code for

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some other module to see if
a given type will work with it.

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Python is still the friendly, strong,
dynamic doc type language we all love, but

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now it has a handy way to make
sure we're using it correctly.

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Thanks for watching.

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And I'll see you next time.