[Baypiggies] Reminder: Introducing Type Annotations for Python TOMORROW (Thursday)

Guido van Rossum guido at python.org
Fri Dec 16 11:01:24 EST 2016

Thanks everyone for showing up last night despite the rain!

Here are the slides we used:

Here is David's Bank example (unannotated, with bugs):

Hopefully the video recording will come online soon.

As a reminder, use "pip install mypy-lang" -- the trailing "-lang" is


On Wed, Dec 14, 2016 at 11:30 AM, Glen Jarvis <glen at glenjarvis.com> wrote:

> Because of the holidays, this is a week earlier than normal. It's tomorrow:
> Also, remember, we're at a new location:
> LinkedIn, Yosemite Room
> 605 W. Maude Ave, Sunnyvale, CA
> Please RSVP to make our lives easier:
> https://www.meetup.com/BAyPIGgies/events/232817503/
> Dropbox has several million lines of production code written in Python
> 2.7. As a first step towards migrating to Python 3, as well as to generally
> make our code more navigable, we are annotating our code with type
> annotations using the PEP 484 standard and type-checking the annotated code
> with mypy. In this talk we will discuss lessons learned and show how you
> too can start type-checking your legacy Python 2.7 code, one file at a
> time. We will also describe some of the many improvements we’ve made to
> mypy in the process, as well as some other tools that come in handy.
> Mypy is an open-source type-checker for Python. It was originally created
> by one of the speakers, Jukka Lehtosalo, in support of his PhD thesis,
> before he joined Dropbox. Mypy supports the PEP 484 standard for gradual
> typing in Python. It supports Python 3.2 and higher, as well as Python 2.7
> (using function signatures in type comments, per a recent update to PEP
> 484).
> Guido van Rossum is the author of the Python programming language. He
> continues to serve as the "Benevolent Dictator For Life" (BDFL), meaning
> that he continues to oversee the Python development process, making
> decisions where necessary. He is currently employed by Dropbox.
> (Based in UK and may not be able to attend)
> Jukka Lehtosalo created mypy, an optional static type checker for Python,
> while working on his PhD at the University of Cambridge. He currently works
> at Dropbox and continues to lead the development of mypy.
> Greg Price is an engineer at Dropbox. Previously he worked at Quora and
> helped Ksplice make rebooting obsolete.
> David Fisher works full time on mypy (the PEP 484 static type checker) at
> Dropbox. He enjoys learning esoteric languages in his spare time.
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--Guido van Rossum (python.org/~guido)
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