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Add section on default object comparison
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‎source-code/object-orientation/attr_intro.ipynb

Lines changed: 199 additions & 3 deletions
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@@ -914,13 +914,209 @@
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" print(f'no luck with {guess}')"
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]
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},
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{
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"cell_type": "markdown",
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"id": "b4a1f9ec-2403-4c86-b41d-b3b22044bc45",
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"metadata": {},
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"source": [
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"## Comparisons"
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]
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},
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{
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"cell_type": "markdown",
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"id": "29040163-48b6-4529-86ad-bb9b6488c8d1",
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"metadata": {},
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"source": [
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"By default, `attrs` will construct comparison methods for you, i.e., `__eq__`, `__neq__`, but also `__lt__` and so on."
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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": 18,
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"id": "d3d21db1-0858-4929-b48a-1df7d69bbb56",
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"metadata": {},
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"outputs": [],
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"source": [
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"@attr.s\n",
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"class Person:\n",
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" lastname: str = attr.ib()\n",
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" firstname: str = attr.ib()\n",
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" age: int = attr.ib()\n",
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" \n",
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" @age.validator\n",
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" def age_validator(self, attribute, value):\n",
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" if value < 0 or value >= 130:\n",
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" raise ValueError(f'age should be between 0 and 130')"
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]
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},
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{
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"cell_type": "markdown",
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"id": "c3567e93-7d09-475c-a225-c482095f829e",
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"metadata": {},
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"source": [
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"The natural order for objects of this class is lexicographic on lastname, firstname, and the numeric on age. Note that the declaration order of the attributes matters and determines the final sort order."
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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": 24,
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"id": "876cfb7a-1697-4bd4-bd78-edd8b5ab8afb",
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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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"[Person(lastname='Zosimo', firstname='Alice', age=43),\n",
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" Person(lastname='Leibovitch', firstname='Aaron', age=31),\n",
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" Person(lastname='Leibovitch', firstname='Robert', age=49),\n",
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" Person(lastname='Zosimo', firstname='Alice', age=25)]"
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]
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},
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"execution_count": 24,
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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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"people = [\n",
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" Person(firstname='Alice', lastname='Zosimo', age=43),\n",
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" Person(firstname='Aaron', lastname='Leibovitch', age=31),\n",
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" Person(firstname='Robert', lastname='Leibovitch', age=49),\n",
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" Person(firstname='Alice', lastname='Zosimo', age=25),\n",
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"]\n",
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"people"
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]
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},
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{
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"cell_type": "markdown",
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"id": "bcf35d6a-596b-4c00-8584-9ba0319d1b10",
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"metadata": {},
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"source": [
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"We can no use Python's `sorted` function to sort the people in this list according to lastname, firstname and age."
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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": 23,
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"id": "82693535-6016-483d-8676-6e87105db263",
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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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"[Person(lastname='Leibovitch', firstname='Aaron', age=31),\n",
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" Person(lastname='Leibovitch', firstname='Robert', age=49),\n",
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" Person(lastname='Zosimo', firstname='Alice', age=25),\n",
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" Person(lastname='Zosimo', firstname='Alice', age=43)]"
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]
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},
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"execution_count": 23,
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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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"sorted(people)"
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]
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},
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{
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"cell_type": "markdown",
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"id": "b7bf5733-4938-4953-9bff-58132ced8c7d",
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"metadata": {},
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"source": [
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"Equality is also based on the object's attributes."
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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": "b84b2436-9a82-4872-a087-71fd4cbe5de4",
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"execution_count": 25,
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"id": "aec2338b-eb7b-4af9-af75-d3c0cf6f62e5",
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"metadata": {},
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"outputs": [],
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"source": []
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"source": [
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"alice1 = Person(firstname='Alice', lastname='Zosimo', age=43)\n",
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"alice2 = Person(firstname='Alice', lastname='Zosimo', age=43)\n",
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"alice3 = Person(firstname='alice', lastname='zosimo', age=43)"
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]
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},
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{
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"cell_type": "markdown",
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"id": "90d4fee2-79c6-430f-9b7b-99c49e87c083",
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"metadata": {},
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"source": [
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"`alice1` has the same attributes as `alice2`, but they are distinct objects nevertheless."
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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": 26,
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"id": "e700a830-20e4-4d95-82d8-17faf8208878",
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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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"True"
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]
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},
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"execution_count": 26,
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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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"alice1 == alice2"
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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": 27,
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"id": "8a90a20b-f421-4744-a536-06eb8892c41e",
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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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"False"
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]
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},
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"execution_count": 27,
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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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"alice1 is alice2"
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]
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},
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{
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"cell_type": "markdown",
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"id": "d32a45c8-0d4e-4f0e-bef8-5e7f1f05751f",
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"metadata": {},
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"source": [
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"`alice3` is different from `alice1`"
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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": 28,
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"id": "ff732001-18bd-44c9-a874-50179a4e9ff1",
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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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"False"
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]
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},
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"execution_count": 28,
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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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"alice1 == alice3"
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]
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}
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],
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"metadata": {

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