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Fred Baptiste
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Part 4/ Section 4 - Polymorphism and Special Methods
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‎Part 4/Section 04 - Polymorphism and Special Methods/01 - __str__ and __repr__ Methods.ipynb

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‎Part 4/Section 04 - Polymorphism and Special Methods/02 - Arithmetic Operators.ipynb

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‎Part 4/Section 04 - Polymorphism and Special Methods/03 - Rich Comparisons.ipynb

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‎Part 4/Section 04 - Polymorphism and Special Methods/04 - Hashing and Equality.ipynb

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‎Part 4/Section 04 - Polymorphism and Special Methods/05 - Booleans.ipynb

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‎Part 4/Section 04 - Polymorphism and Special Methods/06 - Callables.ipynb

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‎Part 4/Section 04 - Polymorphism and Special Methods/07 - The __del__ Method.ipynb

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‎Part 4/Section 04 - Polymorphism and Special Methods/08 - The __format__ Method.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### The `__format__` Method"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"We saw before the use of `__str__` and `__repr__`."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"However we have one more formatting function to look at!\n",
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"\n",
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"The `format()` function."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"For example we can use `format()` with a format specification for floats:"
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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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"metadata": {},
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"outputs": [],
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"source": [
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"a = 0.1"
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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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"metadata": {},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"'0.10000000000000000555'"
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]
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},
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"execution_count": 2,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"format(a, '.20f')"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Or we can use it with a datetime object:"
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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": 3,
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"metadata": {},
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"outputs": [],
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"source": [
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"from datetime import datetime"
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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": 4,
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"metadata": {},
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"outputs": [],
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"source": [
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"now = datetime.utcnow()"
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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": 5,
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"metadata": {},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"datetime.datetime(2019, 6, 13, 3, 43, 48, 904829)"
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]
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},
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"execution_count": 5,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"now"
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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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"metadata": {},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"'Thu 2019-06-13 03:43 AM'"
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]
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},
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"execution_count": 6,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"format(now, '%a %Y-%m-%d %I:%M %p')"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"We can implement support for format specifiers in our own classes by implementing the `__format__` method.\n",
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"\n",
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"This is actually quite complicated to do, so we usually delegate back to some other type's formatting.\n",
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"\n",
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"Just like with `__str__` and `__repr__`, `__format__` should return a string."
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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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"metadata": {},
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"outputs": [],
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"source": [
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"class Person:\n",
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" def __init__(self, name, dob):\n",
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" self.name = name\n",
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" self.dob = dob\n",
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" \n",
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" def __repr__(self):\n",
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" print('__repr__ called...')\n",
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" return f'Person(name={self.name}, dob={self.dob.isoformat()})'\n",
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" \n",
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" def __str__(self):\n",
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" print('__str__ called...')\n",
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" return f'Person({self.name})'\n",
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" \n",
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" def __format__(self, date_format_spec):\n",
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" print(f'__format__ called with {repr(date_format_spec)}...')\n",
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" dob = format(self.dob, date_format_spec)\n",
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" return f'Person(name={self.name}, dob={dob})'"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"So now have:"
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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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"metadata": {},
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"outputs": [],
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"source": [
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"from datetime import date\n",
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"\n",
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"p = Person('Alex', date(1900, 10, 20))"
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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": 9,
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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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"__str__ called...\n"
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]
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},
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{
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"data": {
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"text/plain": [
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"'Person(Alex)'"
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]
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},
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"execution_count": 9,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"str(p)"
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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": 10,
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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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"__repr__ called...\n"
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]
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},
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{
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"data": {
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"text/plain": [
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"'Person(name=Alex, dob=1900-10-20)'"
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]
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},
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"execution_count": 10,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"repr(p)"
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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": 11,
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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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"__format__ called with '%B %d, %Y'...\n"
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]
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},
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{
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"data": {
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"text/plain": [
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"'Person(name=Alex, dob=October 20, 1900)'"
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]
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},
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"execution_count": 11,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"format(p, '%B %d, %Y')"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"If we do not specify a format, then the `format` function will use an empty string:"
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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": 12,
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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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"__format__ called with ''...\n"
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]
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},
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{
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"data": {
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"text/plain": [
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"'Person(name=Alex, dob=1900-10-20)'"
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]
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},
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"execution_count": 12,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"format(p)"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.6.7"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 2
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}

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