Third session fixes and additions

Author: astrojuanlu

sessions/03_pip-vs-conda.ipynb

@@ -10,7 +10,7 @@
    "source": [
     "![IE](../img/ie.png)\n",
     "\n",
-    "# Sessions 4 & 5: pip vs conda\n",
+    "# Sessions 5 & 6: pip vs conda\n",
     "\n",
     "### Juan Luis Cano Rodríguez <jcano@faculty.ie.edu> - Master in Business Analytics and Big Data (2019-04-05)"
    ]
@@ -247,6 +247,50 @@
     "  - <8.x (avoid like the plague!)\n",
     "* As a general rule, _don't upgrade straight away_ - the developers iron the issues after each release"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Project requirements\n",
+    "\n",
+    "We saw in the previous session how to make a project pip-installable. Sometimes our project will depend on third-party libraries (pandas, scikit-learn). To make pip install those dependencies automatically, we can add them to our `setup.cfg` under the `options` section, using the `install_requires` option:\n",
+    "\n",
+    "```\n",
+    "[metadata]\n",
+    "name = my_package\n",
+    "version = 0.1.dev0\n",
+    "\n",
+    "# Remember not to touch package_dir, packages, and where\n",
+    "[options]\n",
+    "install_requires=\n",
+    "    pandas\n",
+    "    matplotlib>=2\n",
+    "package_dir=\n",
+    "    =src\n",
+    "packages=find:\n",
+    "\n",
+    "[options.packages.find]\n",
+    "where=src\n",
+    "```\n",
+    "\n",
+    "On the other hand, we might want to specify _optional_ dependencies that should only be installed upon request, or for some specific purposes. A typical example will be development dependencies: we will need things like pytest and black, but we don't want the user to install them as part as our library. To do that, we can specify *groups* of optional dependencies under the `options.extras_require` section:\n",
+    "\n",
+    "```\n",
+    "[options.extras_require]\n",
+    "dev=\n",
+    "    black\n",
+    "    pytest\n",
+    "```\n",
+    "\n",
+    "That way, they will only get installed when `[dev]` is added after the name of our library:\n",
+    "\n",
+    "```\n",
+    "$ pip install --editable .[dev]\n",
+    "$ # pip install --editable /path/to/library/[dev]  # Absolute instead of relative paths\n",
+    "$ # pip install library[dev]  # Libraries already available in pypi.org\n",
+    "```"
+   ]
   }
  ],
  "metadata": {