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   "source": [
    "# String Methods\n",
    "\n",
    "From an existing string, related strings can be constructed using string methods, which are functions that operate on strings. These methods are called by placing a dot after the string, then calling the function.\n",
    "\n",
    "For example, the following method generates an uppercased version of a string."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'LOUD'"
      ]
     },
     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "\"loud\".upper()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Perhaps the most important method is `replace`, which replaces all instances of a substring within the string. The `replace` method takes two arguments, the text to be replaced and its replacement."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'matchmaker'"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "'hitchhiker'.replace('hi', 'ma')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "String methods can also be invoked using variable names, as long as those names are bound to strings. So, for instance, the following two-step process generates the word \"degrade\" starting from \"train\" by first creating \"ingrain\" and then applying a second replacement."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'degrade'"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s = \"train\"\n",
    "t = s.replace('t', 'ing')\n",
    "u = t.replace('in', 'de')\n",
    "u"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Note that the line `t = s.replace('t', 'ing')` doesn't change the string `s`, which is still \"train\".  The method call `s.replace('t', 'ing')` just has a value, which is the string \"ingrain\"."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'train'"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This is the first time we've seen methods, but methods are not unique to strings.  As we will see shortly, other types of objects can have them."
   ]
  }
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