py2mcp.trans#

Input transformation for py2mcp tools: convert arguments before a function runs.

MCP clients send JSON, so a tool that wants a numpy array, a Path or a parsed date needs its inputs converted first. mk_input_trans builds the input_trans callable that py2mcp.mk_mcp_server(), py2mcp.mk_mcp_from_refs(), and the HTTP/stdio builders that wrap them apply to every tool call, from a mapping of argument names to converter functions. (mk_mcp_from_store’s generated CRUD tools take no input_trans.)

Main entry points:

mk_input_trans: name-to-converter mapping in, input_trans callable out

>>> from py2mcp.trans import mk_input_trans
>>> trans = mk_input_trans({'n': int})
>>> trans({'n': '3', 'label': 'x'})
{'n': 3, 'label': 'x'}

Functions

mk_input_trans([name_func_relationships])

Create an input transformation function from name->func mappings.

py2mcp.trans.mk_input_trans(name_func_relationships=None)[source]#

Create an input transformation function from name->func mappings.

The returned callable takes a tool call’s keyword arguments as a dict and returns a new dict in which each named argument has been passed through its converter; arguments with no converter are copied through unchanged. Pass it as input_trans to py2mcp.mk_mcp_server() and friends.

Parameters:: name_func_relationships (Optional[Mapping]) – Which converter applies to which argument, as {name: func}, or reversed as {func: name} or {func: [name, ...]} when one converter serves several arguments. None gives a transformation that only copies the dict.
Return type:: Callable[[dict], dict]
Returns:: A function from a kwargs dict to a new kwargs dict.
Raises:: ValueError – The same argument name is mapped more than once.

Examples

>>> def to_int(x): return int(x)
>>> trans = mk_input_trans({'x': to_int})
>>> trans({'x': '42', 'y': 'hello'})
{'x': 42, 'y': 'hello'}

One converter for several arguments, written the reversed way:

>>> trans = mk_input_trans({to_int: ['x', 'y']})
>>> trans({'x': '1', 'y': '2', 'z': '3'})
{'x': 1, 'y': 2, 'z': '3'}

No mapping means no conversion:

>>> mk_input_trans()({'x': '1'})
{'x': '1'}