ParamOverrides stops Filename search_paths from working

[ceball]

When fixing the underlying issue, could maybe add a test based on this.

[jbednar]

It looks like what is happening here is that ParamOverrides just returns whatever it finds in its own dict (params here), and thus doesn't perform any special processing that might be done in the __get__ method of any Parameter type. In this case, Path.__get__ (inherited by Filename.__get__) is what does the resolution of a string into a particular file using the search path, and so that step only gets called if there is no value for that parameter in the overrides.

This is a general problem with using ParamOverrides, and it is difficult to see any easy fix. The best I can think of is that anything with a custom __get__ would have to register that somehow for ParamOverrides to discover and use it, which seems very tricky. Anyone have a better idea?

[jbednar]

Here's the .ipynb file to reproduce it, for future reference (using Path, since that's the superclass and it has the same issue):

 "cells": [
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "import param"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "param.__file__"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "class A(param.Parameterized):\n",
    "    path = param.Path(search_paths=['/etc'])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "a = A(path='fstab.hd')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "a.path"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class A2(param.Parameterized):\n",
    "    path = param.Path(search_paths=['/etc'])\n",
    "    def __call__(self,**params):\n",
    "        p = param.ParamOverrides(self,params)\n",
    "        return p.path"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "a2 = A2(path='fstab.hd')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "a2()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "a2(path='fstab.hd')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "A.path"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "a.path"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "a2()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "a2(path=\"fstab.hd\")"
   ]
  }
 ],
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