mirror of
https://github.com/rasbt/python_reference.git
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mutable objects as default arguments
This commit is contained in:
rasbt
parent
be6a8db8cf
commit
f8ebfc8dd0
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@ -1,7 +1,7 @@
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{
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"metadata": {
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"name": "",
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"signature": "sha256:5c0e4a56352cc8a60aa6e2ced2611bc186078af3c849647256f0c4a810004ee9"
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"signature": "sha256:b6e7356842906c447ef3c7520aac098e7fe4f888e46fdd5ae06905f1ebe68e27"
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},
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"nbformat": 3,
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"nbformat_minor": 0,
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@ -48,7 +48,8 @@
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"- [`bool` is a subclass of `int`](#bool_int)\n",
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"- [About lambda and closures-in-a-loop pitfall](#lambda_closure)\n",
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"- [Python's LEGB scope resolution and the keywords `global` and `nonlocal`](#python_legb)\n",
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"- [When immutable Tuples aren't so immutable](#immutable_tuple)"
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"- [When immutable Tuples aren't so immutable](#immutable_tuple)\n",
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"- [List comprehensions are fast, but generators are faster!?](#list_generator)"
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]
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},
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{
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@ -966,7 +967,15 @@
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## List comprehensions are fast, but generators are faster!\n"
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"<br>\n",
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"<br>\n",
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"<a name='list_generator'></a>\n",
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"\n",
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"## List comprehensions are fast, but generators are faster!?\n",
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"\n",
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"Not, really (or significantly, see the benchmarks below). So what's the reason to prefer one over the other?\n",
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"- use lists if you want to use list methods \n",
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"- use generators when you are dealing with huge collections to avoid memory issues"
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]
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},
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{
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@ -975,30 +984,30 @@
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"input": [
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"import timeit\n",
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"\n",
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"def plainlist():\n",
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"def plainlist(n=100000):\n",
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" my_list = []\n",
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" for i in range(1,1000000):\n",
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" for i in range(n):\n",
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" if i % 5 == 0:\n",
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" my_list.append(i)\n",
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" return my_list\n",
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"\n",
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"def listcompr():\n",
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" my_list = [i for i in range(1,1000000) if i % 5 == 0]\n",
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"def listcompr(n=100000):\n",
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" my_list = [i for i in range(n) if i % 5 == 0]\n",
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" return my_list\n",
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"\n",
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"def generator():\n",
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" my_gen = (i for i in range(1,1000000) if i % 5 == 0)\n",
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"def generator(n=100000):\n",
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" my_gen = (i for i in range(n) if i % 5 == 0)\n",
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" return my_gen\n",
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"\n",
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"def generator_yield():\n",
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" for i in range(1,1000000):\n",
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"def generator_yield(n=100000):\n",
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" for i in range(n):\n",
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" if i % 5 == 0:\n",
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" yield i"
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],
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"language": "python",
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"metadata": {},
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"outputs": [],
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"prompt_number": 60
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"prompt_number": 75
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},
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{
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"cell_type": "markdown",
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@ -1027,10 +1036,13 @@
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" for i in listcompr:\n",
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" print(i)\n",
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"\n",
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"print('plain_list', end = '')\n",
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"print('plain_list: ', end = '')\n",
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"%timeit test_plainlist\n",
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"print('\\nlistcompr: ', end = '')\n",
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"%timeit test_listcompr\n",
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"print('\\ngenerator: ', end = '')\n",
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"%timeit test_generator\n",
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"print('\\ngenerator_yield: ', end = '')\n",
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"%timeit test_generator_yield"
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],
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"language": "python",
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@ -1040,28 +1052,45 @@
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"plain_list"
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"plain_list: 10000000 loops, best of 3: 26.2 ns per loop"
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]
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},
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{
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"ename": "NameError",
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"evalue": "global name 'test_plainlist' is not defined",
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"output_type": "pyerr",
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"traceback": [
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"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[0;31mNameError\u001b[0m Traceback (most recent call last)",
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"\u001b[0;32m<ipython-input-62-a2bedd84850f>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m 16\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 17\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m'plain_list'\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mend\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m''\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 18\u001b[0;31m \u001b[0mget_ipython\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mmagic\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m'timeit test_plainlist'\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m 19\u001b[0m \u001b[0mget_ipython\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mmagic\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m'timeit test_listcompr'\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 20\u001b[0m \u001b[0mget_ipython\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mmagic\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m'timeit test_generator'\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
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"\u001b[0;32m/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/IPython/core/interactiveshell.py\u001b[0m in \u001b[0;36mmagic\u001b[0;34m(self, arg_s)\u001b[0m\n\u001b[1;32m 2203\u001b[0m \u001b[0mmagic_name\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0m_\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mmagic_arg_s\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0marg_s\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mpartition\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m' '\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 2204\u001b[0m \u001b[0mmagic_name\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mmagic_name\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mlstrip\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mprefilter\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mESC_MAGIC\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 2205\u001b[0;31m \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mrun_line_magic\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmagic_name\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mmagic_arg_s\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m 2206\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 2207\u001b[0m \u001b[0;31m#-------------------------------------------------------------------------\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
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"\u001b[0;32m/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/IPython/core/interactiveshell.py\u001b[0m in \u001b[0;36mrun_line_magic\u001b[0;34m(self, magic_name, line)\u001b[0m\n\u001b[1;32m 2124\u001b[0m \u001b[0mkwargs\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;34m'local_ns'\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0msys\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_getframe\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mstack_depth\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mf_locals\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 2125\u001b[0m \u001b[0;32mwith\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mbuiltin_trap\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 2126\u001b[0;31m \u001b[0mresult\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mfn\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m*\u001b[0m\u001b[0margs\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m**\u001b[0m\u001b[0mkwargs\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m 2127\u001b[0m \u001b[0;32mreturn\u001b[0m \u001b[0mresult\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 2128\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
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"\u001b[0;32m/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/IPython/core/magics/execution.py\u001b[0m in \u001b[0;36mtimeit\u001b[0;34m(self, line, cell)\u001b[0m\n",
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"\u001b[0;32m/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/IPython/core/magic.py\u001b[0m in \u001b[0;36m<lambda>\u001b[0;34m(f, *a, **k)\u001b[0m\n\u001b[1;32m 191\u001b[0m \u001b[0;31m# but it's overkill for just that one bit of state.\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 192\u001b[0m \u001b[0;32mdef\u001b[0m \u001b[0mmagic_deco\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0marg\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 193\u001b[0;31m \u001b[0mcall\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;32mlambda\u001b[0m \u001b[0mf\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m*\u001b[0m\u001b[0ma\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m**\u001b[0m\u001b[0mk\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mf\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m*\u001b[0m\u001b[0ma\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m**\u001b[0m\u001b[0mk\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m 194\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 195\u001b[0m \u001b[0;32mif\u001b[0m \u001b[0mcallable\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0marg\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
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"\u001b[0;32m/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/IPython/core/magics/execution.py\u001b[0m in \u001b[0;36mtimeit\u001b[0;34m(self, line, cell)\u001b[0m\n\u001b[1;32m 1011\u001b[0m \u001b[0mnumber\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;36m1\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 1012\u001b[0m \u001b[0;32mfor\u001b[0m \u001b[0m_\u001b[0m \u001b[0;32min\u001b[0m \u001b[0mrange\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m10\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 1013\u001b[0;31m \u001b[0;32mif\u001b[0m \u001b[0mtimer\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mtimeit\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mnumber\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;34m>=\u001b[0m \u001b[0;36m0.2\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m 1014\u001b[0m \u001b[0;32mbreak\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 1015\u001b[0m \u001b[0mnumber\u001b[0m \u001b[0;34m*=\u001b[0m \u001b[0;36m10\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
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"\u001b[0;32m/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/timeit.py\u001b[0m in \u001b[0;36mtimeit\u001b[0;34m(self, number)\u001b[0m\n\u001b[1;32m 188\u001b[0m \u001b[0mgc\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mdisable\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 189\u001b[0m \u001b[0;32mtry\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 190\u001b[0;31m \u001b[0mtiming\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0minner\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mit\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mtimer\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m 191\u001b[0m \u001b[0;32mfinally\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 192\u001b[0m \u001b[0;32mif\u001b[0m \u001b[0mgcold\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
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"\u001b[0;32m<magic-timeit>\u001b[0m in \u001b[0;36minner\u001b[0;34m(_it, _timer)\u001b[0m\n",
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"\u001b[0;31mNameError\u001b[0m: global name 'test_plainlist' is not defined"
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"\n",
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"\n",
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"listcompr: 10000000 loops, best of 3: 26.1 ns per loop"
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]
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},
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{
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"\n",
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"\n",
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"generator: 10000000 loops, best of 3: 25.9 ns per loop"
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]
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},
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{
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"\n",
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"\n",
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"generator_yield: 10000000 loops, best of 3: 26 ns per loop"
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]
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},
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{
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"\n"
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]
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}
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],
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"prompt_number": 62
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"prompt_number": 76
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},
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{
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"cell_type": "code",
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@ -1,7 +1,7 @@
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{
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"metadata": {
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"name": "",
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"signature": "sha256:a2c062243bccabbfe46e6f62bbc9d6dd5b10fe44d091727781108ba5b87b9e28"
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"signature": "sha256:b6e7356842906c447ef3c7520aac098e7fe4f888e46fdd5ae06905f1ebe68e27"
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},
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"nbformat": 3,
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"nbformat_minor": 0,
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@ -48,7 +48,8 @@
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"- [`bool` is a subclass of `int`](#bool_int)\n",
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"- [About lambda and closures-in-a-loop pitfall](#lambda_closure)\n",
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"- [Python's LEGB scope resolution and the keywords `global` and `nonlocal`](#python_legb)\n",
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"- [When immutable Tuples aren't so immutable](#immutable_tuple)"
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"- [When immutable Tuples aren't so immutable](#immutable_tuple)\n",
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"- [List comprehensions are fast, but generators are faster!?](#list_generator)"
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]
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},
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{
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|
|
@ -967,9 +968,10 @@
|
|||
"metadata": {},
|
||||
"source": [
|
||||
"<br>\n",
|
||||
"<br>\n",
|
||||
"<a name='list_generator'></a>\n",
|
||||
"\n",
|
||||
"\n",
|
||||
"## List comprehensions are fast, but generators are faster!\n",
|
||||
"## List comprehensions are fast, but generators are faster!?\n",
|
||||
"\n",
|
||||
"Not, really (or significantly, see the benchmarks below). So what's the reason to prefer one over the other?\n",
|
||||
"- use lists if you want to use list methods \n",
|
||||
|
|
@ -1018,8 +1020,6 @@
|
|||
"cell_type": "code",
|
||||
"collapsed": false,
|
||||
"input": [
|
||||
"\n",
|
||||
"\n",
|
||||
"def test_plainlist(plain_list):\n",
|
||||
" for i in plain_list:\n",
|
||||
" print(i)\n",
|
||||
|
|
|
|||
Loading…
Reference in New Issue
Block a user