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‎book/111_debugging.ipynb‎

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"metadata": {},
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"source": [
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"We are humans, we make mistakes – that's very much true for coding.\n",
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"Finding errors in our code is fundamental skill to train.\n",
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"\n",
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"We will cover here a few tools that help us find and fix errors more quickly."
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"Finding errors in our code is fundamental skill to train so we will cover here a few tools that help us find and fix errors more quickly."
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]
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},
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{
@@ -32,7 +31,7 @@
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"A debugger is a device that allows us to interrupt code execution and jump into the execution context in a interactive mode, so that we can inspect and run code to find out what's going on. \n",
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"We called that to \"set a breakpoint\" or \"set a trace\".\n",
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"\n",
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"There are a few options to do that natively in python."
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"There are a few options to do that in python."
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]
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},
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{
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"source": [
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"## Python debugger, breakpoints\n",
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"The python standard library includes `pdb` module.\n",
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"If you call this function in your code you will be put into an interactive session exactly at that point.\n",
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"\n",
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"Any of the following options would work:\n",
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"\n",
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"```python\n",
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"import pdb; pdb.set_trace()\n",
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"# your code\n",
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"# your code\n",
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"import pdb\n",
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"pdb.set_trace()\n",
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"# your code\n",
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"# your code\n",
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"breakpoint()\n",
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"# your code\n",
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"# your code\n",
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"# your code\n",
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"```"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"id": "b40ea608-89a9-4cbd-b07f-4f9a33699d89",
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"cell_type": "markdown",
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"id": "1a6d1185-f23d-4fd1-80ee-925836018ef8",
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"metadata": {},
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"outputs": [],
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"source": []
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"source": [
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"Once in the debugger, we have several functions to proceed with code execution with more granular control.\n",
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"\n",
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"There are several options, but the most commonly used methods are:\n",
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"\n",
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"- n (next): Continue execution one line, stay in the current function (step over)\n",
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"- s (step): Execute current line and stop in a foreign function if one is called (step into) \n",
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"- c (continue): Continue whole code execution until a new breakpoint is found"
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]
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},
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{
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"cell_type": "markdown",
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"id": "4ae14f36-84e6-4def-9240-7a423c587e9c",
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"metadata": {},
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"source": [
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"## IPython debugger"
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"## IPython debugger\n",
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"The standard python debugger is fine but a bit basic, so sometimes the IPython debugger is a friendlier option.\n",
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"\n",
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"We need to install it:\n",
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"\n",
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"```bash\n",
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"uv add ipdb\n",
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"```\n",
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"Then we can do:\n",
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"\n",
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"```python\n",
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"import ipdb\n",
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"ipdb.set_trace()\n",
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"```"
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]
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},
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{
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"cell_type": "markdown",
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"id": "886ba261-d3a3-43e0-b7e1-3353d0029622",
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"metadata": {},
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"source": [
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"## Notebook %%debug"
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"## Notebook %debug\n",
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"Inside the jupyter notebook we can directly jump into a debugger when there is an error.\n",
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"\n",
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"If a cell throws an error, you can type this \"ipython magic method\" in the following cell:\n",
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"\n",
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"```python\n",
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"%debug\n",
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"```"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"id": "76c6445c-3cc0-4bc6-b602-97cd5707feee",
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"metadata": {},
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"outputs": [
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{
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"ename": "AssertionError",
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"evalue": "",
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"output_type": "error",
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"traceback": [
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"\u001b[31m---------------------------------------------------------------------------\u001b[39m",
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"\u001b[31mAssertionError\u001b[39m Traceback (most recent call last)",
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"\u001b[36mCell\u001b[39m\u001b[36m \u001b[39m\u001b[32mIn[1]\u001b[39m\u001b[32m, line 5\u001b[39m\n\u001b[32m 2\u001b[39m a = \u001b[32m1\u001b[39m\n\u001b[32m 3\u001b[39m \u001b[38;5;28;01massert\u001b[39;00m a == \u001b[32m0\u001b[39m\n\u001b[32m----> \u001b[39m\u001b[32m5\u001b[39m \u001b[43mwrong_func\u001b[49m\u001b[43m(\u001b[49m\u001b[43m)\u001b[49m\n",
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"\u001b[36mCell\u001b[39m\u001b[36m \u001b[39m\u001b[32mIn[1]\u001b[39m\u001b[32m, line 3\u001b[39m, in \u001b[36mwrong_func\u001b[39m\u001b[34m()\u001b[39m\n\u001b[32m 1\u001b[39m \u001b[38;5;28;01mdef\u001b[39;00m\u001b[38;5;250m \u001b[39m\u001b[34mwrong_func\u001b[39m():\n\u001b[32m 2\u001b[39m a = \u001b[32m1\u001b[39m\n\u001b[32m----> \u001b[39m\u001b[32m3\u001b[39m \u001b[38;5;28;01massert\u001b[39;00m a == \u001b[32m0\u001b[39m\n",
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"\u001b[31mAssertionError\u001b[39m: "
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]
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}
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],
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"source": [
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"def wrong_func():\n",
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" a = 1\n",
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" assert a == 0\n",
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"\n",
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"wrong_func()"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"id": "9225666f-7cce-4bec-96ac-c5fc1f167968",
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"> \u001b[32m/tmp/ipykernel_81865/3667203143.py\u001b[39m(\u001b[92m3\u001b[39m)\u001b[36mwrong_func\u001b[39m\u001b[34m()\u001b[39m\n",
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"\u001b[32m 1\u001b[39m \u001b[38;5;28;01mdef\u001b[39;00m wrong_func():\n",
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"\u001b[32m 2\u001b[39m a = \u001b[32m1\u001b[39m\n",
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"\u001b[32m----> 3\u001b[39m \u001b[38;5;28;01massert\u001b[39;00m a == \u001b[32m0\u001b[39m\n",
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"\u001b[32m 4\u001b[39m \n",
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"\u001b[32m 5\u001b[39m wrong_func()\n",
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"\n"
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]
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},
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{
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"name": "stdin",
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"output_type": "stream",
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"text": [
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"ipdb> print(a)\n"
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]
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},
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"1\n"
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]
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},
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{
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"name": "stdin",
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"output_type": "stream",
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"text": [
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"ipdb> exit\n"
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]
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}
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],
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"source": [
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"%debug"
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]
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},
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{
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"cell_type": "markdown",
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"id": "fac0dd96-22c9-40a8-b279-e5043f415fa9",
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"metadata": {},
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"source": [
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"Notice that we typed \"exit\" to get out of the debugger."
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]
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},
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{
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"cell_type": "markdown",
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"id": "7995bd99-3ba9-49d5-8c18-2b289f999133",
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"metadata": {},
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"source": [
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"## Exercises\n",
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"\n",
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"Here's a piece of code that will fail at run-time:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 8,
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"id": "abb2830e-8f39-4bad-9f1c-cc0dd697f09c",
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"metadata": {},
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"outputs": [],
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"source": [
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"def f(p):\n",
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" assert p == 0\n",
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" \n",
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"def main():\n",
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" a = 0\n",
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" f(a)\n",
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" b = 1 \n",
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" f(b)\n",
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" c = 0\n",
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" f(c)"
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]
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},
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{
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"cell_type": "markdown",
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"id": "8275e207-c5b3-4242-832e-4f98d30f1145",
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"metadata": {},
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"source": [
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"1) Run the code to see the error\n",
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"2) Set a breakpoint inside `main` to use the debugger\n",
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"3) Step through the code using `n (next)` and another time using `s (step)`\n",
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"4) Set a second breakpoint inside `main`and run again the code but this time use `c (continue)`\n",
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"5) Download [this public dataset](https://github.com/fabridamicelli/ds005588/archive/refs/heads/broken-data.zip) into the folder `/pycourse/data/` (create it if you don't yet have it).\n",
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"\n",
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"This dataset was modified and has some problems apparently.\n",
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"Here's a bit of code to unzip it and read through the files."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 6,
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"id": "bbe54d2f-f5a4-44f1-a015-8a4d19e1097a",
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"metadata": {},
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"outputs": [],
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"source": [
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"path = \"/home/fdamicel/projects/pycourse/data/ds005588-broken-data.zip\"\n",
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"target = \"/home/fdamicel/projects/pycourse/data\""
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]
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},
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{
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"cell_type": "code",
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"execution_count": 7,
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"id": "e7ad9b30-c041-4edc-83d4-2cfdf984dac7",
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"metadata": {},
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"outputs": [],
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"source": [
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"import zipfile"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 8,
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"id": "123149ab-4410-4444-9348-099cbf067f91",
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"metadata": {},
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"outputs": [],
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"source": [
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"with zipfile.ZipFile(path) as file:\n",
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" file.extractall(target)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 13,
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"id": "8d95f7c4-977f-4cc5-8f8e-80e87ec7d40a",
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"metadata": {},
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"outputs": [],
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"source": []
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},
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{
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"cell_type": "code",
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"execution_count": 14,
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"id": "3f764de2-552c-49ab-ae8c-8d8455d254c3",
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"metadata": {},
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"outputs": [],
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"source": []
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},
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{
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"cell_type": "code",
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"execution_count": 15,
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"id": "4fbd3efe-bd52-4414-99a5-42058984a3c8",
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"metadata": {},
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"outputs": [
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{
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"ename": "UnicodeDecodeError",
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"evalue": "'utf-8' codec can't decode byte 0xb9 in position 10: invalid start byte",
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"output_type": "error",
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"traceback": [
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"\u001b[31m---------------------------------------------------------------------------\u001b[39m",
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"\u001b[31mUnicodeDecodeError\u001b[39m Traceback (most recent call last)",
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"\u001b[36mCell\u001b[39m\u001b[36m \u001b[39m\u001b[32mIn[15]\u001b[39m\u001b[32m, line 1\u001b[39m\n\u001b[32m----> \u001b[39m\u001b[32m1\u001b[39m lines = \u001b[43mf\u001b[49m\u001b[43m.\u001b[49m\u001b[43mreadlines\u001b[49m\u001b[43m(\u001b[49m\u001b[43m)\u001b[49m\n",
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"\u001b[36mFile \u001b[39m\u001b[32m<frozen codecs>:325\u001b[39m, in \u001b[36mdecode\u001b[39m\u001b[34m(self, input, final)\u001b[39m\n",
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"\u001b[31mUnicodeDecodeError\u001b[39m: 'utf-8' codec can't decode byte 0xb9 in position 10: invalid start byte"
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]
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}
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],
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"source": []
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"id": "4877305d-66bb-47ab-95c9-ae9377323bef",
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"metadata": {},
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"outputs": [],
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"source": []
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}
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],
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"metadata": {

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