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pajannepajanne
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improve explanation of comparing objects values and references using == and is
1 parent 1092333 commit 27a7102

2 files changed

Lines changed: 111 additions & 26 deletions

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‎python_basic_2_1.ipynb‎

Lines changed: 57 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -100,7 +100,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"x = -3\n",
@@ -160,7 +162,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"gene = \"BRCA2\"\n",
@@ -187,7 +191,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"x = 11\n",
@@ -231,7 +237,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"x = -5\n",
@@ -247,9 +255,36 @@
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Python has two additional comparison operators <tt>is</tt> and <tt>is not</tt>. These compare whether two objects are the same object, whereas <tt>==</tt> and <tt>!=</tt> compare whether values are the same.\n",
258+
"Python has two additional comparison operators <tt>is</tt> and <tt>is not</tt>.\n",
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"\n",
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"These compare whether two objects are the same object, whereas <tt>==</tt> and <tt>!=</tt> compare whether values are the same.\n",
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"\n",
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"There is a simple rule of thumb to tell when to use `==` or `is`:\n",
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"- `==` is for **value** equality. Use it to check if two objects have the same value.\n",
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"- `is` is for **reference** equality. Use it to check if two references refer to the same object.\n",
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"\n",
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"As an example in Python:"
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"*Something to note*, you will get unexpected and inconsistent results if you mistakenly use `is` to compare for reference equality on integers:"
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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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"metadata": {},
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"outputs": [],
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"source": [
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"a = 500\n",
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"b = 500\n",
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"print(a == b) # True\n",
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"print(a is b) # False"
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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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"Another example with lists `x`, `y`, and `z`:\n",
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"- `y` being a copy of `x`\n",
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"- and `z` being another reference to the same object as `x`"
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]
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},
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{
@@ -262,13 +297,25 @@
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"y = x[:] # y is a copy of x\n",
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"z = x\n",
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"print(x)\n",
300+
"print(y)\n",
301+
"print(z)\n",
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"print(\"Are values of y and x the same?\", y == x)\n",
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"print(\"Are objects y and x the same?\", y is x)\n",
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"print(\"Are values of z and x the same?\", z == x)\n",
268-
"print(\"Are objects z and x the same?\", z is x)\n",
305+
"print(\"Are objects z and x the same?\", z is x)"
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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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"metadata": {},
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"outputs": [],
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"source": [
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"# Let's change x\n",
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"x[1] = 23\n",
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"print(x)\n",
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"print(y)\n",
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"print(z)\n",
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"print(\"Are values of y and x the same?\", y == x)\n",
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"print(\"Are objects y and x the same?\", y is x)\n",
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"print(\"Are values of z and x the same?\", z == x)\n",
@@ -299,7 +346,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"x = '' # An empty string\n",

‎python_basic_2_2.ipynb‎

Lines changed: 54 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -52,7 +52,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"codeList = ['NA06984', 'NA06985', 'NA06986', 'NA06989', 'NA06991']\n",
@@ -71,7 +73,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"dnaSequence = 'ATGGTGTTGCC'\n",
@@ -90,7 +94,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"rnaMassDict = {\"G\":345.21, \"C\":305.18, \"A\":329.21, \"U\":302.16}\n",
@@ -109,7 +115,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"total = 0\n",
@@ -133,7 +141,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"geneExpression = {\n",
@@ -184,7 +194,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"value = 0.25\n",
@@ -229,7 +241,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"values = [10, -5, 3, -1, 7]\n",
@@ -253,7 +267,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"geneticCode = {'TAT': 'Tyrosine', 'TAC': 'Tyrosine',\n",
@@ -316,7 +332,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"print(list(range(10)))\n",
@@ -338,7 +356,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"for x in range(8):\n",
@@ -348,7 +368,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"squares = []\n",
@@ -376,7 +398,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"letters = ['A','C','G','T']\n",
@@ -387,7 +411,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"numbered_letters = list(enumerate(letters))\n",
@@ -404,7 +430,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"city_pops = {\n",
@@ -425,7 +453,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"total = 0\n",
@@ -437,7 +467,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"pops = list(city_pops.values())\n",
@@ -464,7 +496,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"print('{:.2f}'.format(0.4567))"
@@ -473,7 +507,9 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"geneExpression = {\n",

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