输入数据的验证需要注意！！！

Constructs a transformer from an arbitrary callable.

A FunctionTransformer forwards its X (and optionally y) arguments to a user-defined function or function object and returns the result of this function. This is useful for stateless transformations such as taking the log of frequencies, doing custom scaling, etc.

Note: If a lambda is used as the function, then the resulting transformer will not be pickleable.

New in version 0.17.

Read more in the User Guide.

Parameters:
func : callable, optional default=None
The callable to use for the transformation. This will be passed the same arguments as transform, with args and kwargs forwarded. If func is None, then func will be the identity function.

inverse_func : callable, optional default=None
The callable to use for the inverse transformation. This will be passed the same arguments as inverse transform, with args and kwargs forwarded. If inverse_func is None, then inverse_func will be the identity function.

validate : bool, optional default=True
Indicate that the input X array should be checked before calling func. The possibilities are:

If False, there is no input validation.
If True, then X will be converted to a 2-dimensional NumPy array or sparse matrix. If the conversion is not possible an exception is raised.
Deprecated since version 0.20: validate=True as default will be replaced by validate=False in 0.22.
accept_sparse : boolean, optional
Indicate that func accepts a sparse matrix as input. If validate is False, this has no effect. Otherwise, if accept_sparse is false, sparse matrix inputs will cause an exception to be raised.

pass_y : bool, optional default=False
Indicate that transform should forward the y argument to the inner callable.

check_inverse : bool, default=True
Whether to check that or func followed by inverse_func leads to the original inputs. It can be used for a sanity check, raising a warning when the condition is not fulfilled.

New in version 0.20.

kw_args : dict, optional
Dictionary of additional keyword arguments to pass to func.

inv_kw_args : dict, optional
Dictionary of additional keyword arguments to pass to inverse_func.