Comment by ossopite | Hacker News Reader

Comment by ossopite | Hacker News Reader

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The most important difference in my experience has been that pyright is a lot more rigorous and correct than mypy. I found that it was easy to confuse mypy, leaving large amounts of code unexpectedly not type checked. Put simply, I trust pyright and I do not trust mypy.

You also have a lot more control with pyright over where unknown types are permitted or what other checks should be performed. Also, it can scan library source code to infer types which I don't think mypy supports.

My experience is much the same: pyright is fast, reliable, and (when it complains) correct. MyPy is… not always those things. The teams I know that use Python generally have all moved to pyright if they started with MyPy.

The lack of plug-in support might feel like a hang-up, for instance if you’re using Django. FWIW, I like the “no plug-in” philosophy. I’ve discovered that explicitly adding annotations that a MyPy plug-in would have surmised feels cleaner. (Example: an annotation for a reverse collection on a Model referenced by a foreign key.) Even better: I don’t need to suffer the (in my experience) frequent bugs of the plugins themselves.

An example of where mypy chokes:

  def foo(data: list[str]):
    r = []                        # error: Need type annotation
    for key in data:
      r.append(key if len(r) > 0 else '')
    return r

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