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mutable objects as default arguments

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rasbt 2014-04-15 16:46:46 -04:00
parent 9483e549c3
commit 00d6839d17
2 changed files with 142 additions and 4 deletions
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73
.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
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@ -1,7 +1,7 @@
{
"metadata": {
"name": "",
"signature": "sha256:913662e78e4e0a2e83e289d74c42e197b1d5af6c2f589057de821734b0141c07"
"signature": "sha256:7eaf1c17c09445d2807a0560a73437a138201e67de0b44e98b6c853eff059061"
},
"nbformat": 3,
"nbformat_minor": 0,
@ -43,7 +43,8 @@
"- [Python reuses objects for small integers - always use \"==\" for equality, \"is\" for identity](#python_small_int)\n",
"- [Shallow vs. deep copies if list contains other structures and objects](#shallow_vs_deep)\n",
"- [Picking True values from and and or expressions](#false_true_expressions)\n",
"- [Don't use mutable objects as default arguments for functions!](#def_mutable_func)"
"- [Don't use mutable objects as default arguments for functions!](#def_mutable_func)\n",
"- [Be aware of the consuming generator](#consuming_generator)"
]
},
{
@ -466,6 +467,74 @@
],
"prompt_number": 1
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"<br>\n",
"<br>\n",
"<a name='consuming_generators'></a>\n",
"\n",
"## Be aware of the consuming generator\n",
"\n",
"Be aware using `in` checks with generators, since they won't evaluate from the beginning once a position is \"consumed\"."
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"gen = (i for i in range(5))\n",
"print('2 in gen,', 2 in gen)\n",
"print('3 in gen,', 3 in gen)\n",
"print('1 in gen,', 1 in gen) "
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"2 in gen, True\n",
"3 in gen, True\n",
"1 in gen, False\n"
]
}
],
"prompt_number": 9
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**We can circumvent this problem by using a simple list, though:**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"l = [i for i in range(5)]\n",
"print('2 in l,', 2 in l)\n",
"print('3 in l,', 3 in l)\n",
"print('1 in l,', 1 in l) "
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"2 in l, True\n",
"3 in l, True\n",
"1 in l, True\n"
]
}
],
"prompt_number": 10
},
{
"cell_type": "code",
"collapsed": false,

73
not_so_obvious_python_stuff.ipynb
View File

@ -1,7 +1,7 @@
{
"metadata": {
"name": "",
"signature": "sha256:913662e78e4e0a2e83e289d74c42e197b1d5af6c2f589057de821734b0141c07"
"signature": "sha256:7eaf1c17c09445d2807a0560a73437a138201e67de0b44e98b6c853eff059061"
},
"nbformat": 3,
"nbformat_minor": 0,
@ -43,7 +43,8 @@
"- [Python reuses objects for small integers - always use \"==\" for equality, \"is\" for identity](#python_small_int)\n",
"- [Shallow vs. deep copies if list contains other structures and objects](#shallow_vs_deep)\n",
"- [Picking True values from and and or expressions](#false_true_expressions)\n",
"- [Don't use mutable objects as default arguments for functions!](#def_mutable_func)"
"- [Don't use mutable objects as default arguments for functions!](#def_mutable_func)\n",
"- [Be aware of the consuming generator](#consuming_generator)"
]
},
{
@ -466,6 +467,74 @@
],
"prompt_number": 1
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"<br>\n",
"<br>\n",
"<a name='consuming_generators'></a>\n",
"\n",
"## Be aware of the consuming generator\n",
"\n",
"Be aware using `in` checks with generators, since they won't evaluate from the beginning once a position is \"consumed\"."
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"gen = (i for i in range(5))\n",
"print('2 in gen,', 2 in gen)\n",
"print('3 in gen,', 3 in gen)\n",
"print('1 in gen,', 1 in gen) "
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"2 in gen, True\n",
"3 in gen, True\n",
"1 in gen, False\n"
]
}
],
"prompt_number": 9
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**We can circumvent this problem by using a simple list, though:**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"l = [i for i in range(5)]\n",
"print('2 in l,', 2 in l)\n",
"print('3 in l,', 3 in l)\n",
"print('1 in l,', 1 in l) "
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"2 in l, True\n",
"3 in l, True\n",
"1 in l, True\n"
]
}
],
"prompt_number": 10
},
{
"cell_type": "code",
"collapsed": false,