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    "# How to convert ordinary string to an f-string or evaluate an ordinary string as an f-string?\n",
    "\n",
    "At this month's COhPy meeting,\n",
    "someone asked how to either\n",
    "convert an ordinary string to an f-string\n",
    "or evaluate an ordinary string as an f-string.\n",
    "\n",
    "One solution is to use eval() as shown below.\n",
    "What other solutions are there?\n",
    "\n",
    "Why was %r used instead of %s or %a in the first eval expression?"
   ]
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     "name": "stdout",
     "output_type": "stream",
     "text": [
      "iso:\n",
      "2017-03-27\n",
      "2017-04-24\n",
      "2017-05-22\n",
      "us:\n",
      "3/27/2017\n",
      "4/24/2017\n",
      "5/22/2017\n",
      "other:\n",
      "27 3 2017\n",
      "24 4 2017\n",
      "22 5 2017\n"
     ]
    }
   ],
   "source": [
    "date_formats = {\n",
    "    'iso': '{year}-{month:02d}-{day:02d}',\n",
    "    'us': '{month}/{day}/{year}',\n",
    "    'other': '{day} {month} {year}',\n",
    "}\n",
    "dates = (\n",
    "    (2017, 3, 27),\n",
    "    (2017, 4, 24),\n",
    "    (2017, 5, 22),\n",
    ")\n",
    "\n",
    "for format_name, format in date_formats.items():\n",
    "    print(f'{format_name}:')\n",
    "    for year, month, day in dates:\n",
    "        print(eval('f%r' % format))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
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   "source": [
    "One surprise for me is that this is another way of deferring\n",
    "evaluation of f-strings, and that it is easier to read than\n",
    "using lambdas. I wonder how much slower eval() is than using\n",
    "the lambdas."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
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   "source": [
    "Which of the following is easier for you read?\n",
    "Why/how?\n",
    "\n",
    "    print(eval('f%r' % format))\n",
    "    print(eval(f'f{format!r}'))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
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   },
   "source": [
    "I wonder what sympy thinks of manipulating f-strings."
   ]
  }
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