index.html

$title mypy - Optional Static Typing for Python$
$keywords mypy, mypy language, python static typing, python, python optional styping, optional typing, python type checker$
$description Mypy is an optional static type checker for Python.$

  <div id="rightbar">
    <div id="fork" class="rightbox">
      <a href="https://github.com/python/mypy">Get the Code on GitHub!</a>
    </div>
    <div id="twitter" class="rightbox">
      <b>Mypy on Twitter is @mypyproject</b>
      <p><a href="https://twitter.com/mypyproject">Follow @mypyproject on
      Twitter</a>
    </div>
    <div id="why" class="rightbox">
      <div class="title">Why mypy?</div>
      <dl>
        <dt><b>Compile-time type checking</b>
        <dd>Static typing makes it easier to find bugs
          with less debugging.
        <dt><b>Easier maintenance</b>
        <dd>Type declarations act as
           machine-checked documentation.
           Static typing makes your code easier to understand and easier to modify
           without introducing bugs.
        <dt><b>Grow your programs from dynamic to static</b>
          typing
        <dd>You can develop programs with dynamic typing and add
          static typing after your code has matured, or migrate existing
          Python code to static typing.
      </dl>
    </div>
  </div>

    <h1 id="mypy-heading">mypy</h1>

    <div id="desc">
    Mypy is an optional static type checker for Python that aims
    to combine the benefits of dynamic (or "duck") typing and static typing.
    Mypy combines the expressive power and
    convenience of Python with a powerful type system and compile-time type checking.
    Mypy type checks standard Python programs; run them using any Python VM
    with basically no runtime overhead.
    </div>

    <h1>What's new</h1>

    $latestnews$

    <p><a href="news.html">Older news</a>

    <h1>Seamless dynamic and static typing</h1>

    <div class="front-sample">
    <div class="sample-header">From Python...</div>
    $code!
||def fib(n)||:
    a, b = 0, 1
    while a < n:
        yield a
        a, b = b, a+b
!
    </div>
    <div class="front-sample">
    <div class="sample-header">...to statically typed Python</div>
    $code!
||def fib(n: int) -> Iterator[int]||:
    a, b = 0, 1
    while a < n:
        yield a
        a, b = b, a+b
!
    </div>
    <div class="clear-left"></div>

    <p>Migrate existing code to static typing, a function at a time.
      You can freely mix static and dynamic typing within a program, within
      a module or within an expression. No need to
      give up dynamic typing &#8212; use static typing
      when it makes sense.
    Often just adding function signatures gives you statically typed code.
    Mypy can infer the types of other
    variables.

    <h1>Python syntax</h1>

    <p>Mypy type checks programs that have type annotations conforming to
    <a href="https://www.python.org/dev/peps/pep-0484/">PEP 484</a>.
    Getting started is easy if you know Python.
    The aim is to support almost all Python language constructs in mypy.

    <h1>Powerful type system</h1>

    <p>Mypy has a powerful, modern type system with features such as bidirectional type inference,
    generics, callable types, abstract base classes, multiple inheritance and tuple types.

    <h1>Access to Python libs</h1>

    <p>Many commonly used libraries have stubs (statically typed interface
    definitions) that allow mypy to check that your code uses the
    libraries correctly.

    <div id="learn-more">
      $include(learn.html)$
    </div>