Static inference of annotations

The mypy daemon supports (as an experimental feature) statically inferringdraft function and method type annotations. Use dmypy suggest FUNCTION togenerate a draft signature in the format(param_type_1, param_type_2, …) -> ret_type (types are included for allarguments, including keyword-only arguments, args and *kwargs).

This is a low-level feature intended to be used by editor integrations,IDEs, and other tools (for example, the mypy plugin for PyCharm),to automatically add annotations to source files, or to propose functionsignatures.

In this example, the function format_id() has no annotation:

def format_id(user):
    return "User: {}".format(user)
 
root = format_id(0)

dymypy suggest uses call sites, return statements, and other heuristics (such aslooking for signatures in base classes) to infer that format_id() acceptsan int argument and returns a str. Use dmypy suggest module.format_id toprint the suggested signature for the function.

More generally, the target function may be specified in two ways:

• By its fully qualified name, i.e. [package.]module.[class.]function.
• By its location in a source file, i.e. /path/to/file.py:line. The path can beabsolute or relative, and line can refer to any line number withinthe function body.

This command can also be used to find a more precise alternative for an existing,imprecise annotation with some Any types.

The following flags customize various aspects of the dmypy suggestcommand.

• —json
• Output the signature as JSON, so that PyAnnotate can read it and addthe signature to the source file. Here is what the JSON looks like:

[{"func_name": "example.format_id",
  "line": 1,
  "path": "/absolute/path/to/example.py",
  "samples": 0,
  "signature": {"arg_types": ["int"], "return_type": "str"}}]

• —no-errors
• Only produce suggestions that cause no errors in the checked code. By default,mypy will try to find the most precise type, even if it causes some type errors.

• —no-any
• Only produce suggestions that don’t contain Any types. By default mypyproposes the most precise signature found, even if it contains Any types.

• —flex-any FRACTION
• Only allow some fraction of types in the suggested signature to be Any types.The fraction ranges from 0 (same as —no-any) to 1.

• —try-text
• Try also using unicode wherever str is inferred. This flag may be usefulfor annotating Python 2/3 straddling code.

• —callsites
• Only find call sites for a given function instead of suggesting a type.This will produce a list with line numbers and types of actualarguments for each call: /path/to/file.py:line: (arg_type_1, arg_type_2, …).

• —use-fixme NAME
• Use a dummy name instead of plain Any for types that cannotbe inferred. This may be useful to emphasize to a user that a given typecouldn’t be inferred and needs to be entered manually.

• —max-guesses NUMBER
• Set the maximum number of types to try for a function (default: 64).