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mutable objects as default arguments

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rasbt 2014-04-15 15:44:09 -04:00
parent 6c95918f3d
commit ed255a9ad7
2 changed files with 112 additions and 2 deletions
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57
.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
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@ -1,7 +1,7 @@
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"<br>\n",
"<br>\n",
"<a name='def_mutable_func></a>\n",
"## Don't use mutable objects as default arguments for functions!"
]
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"Don't use mutable objects (e.g., dictionaries, lists, sets, etc.) as default arguments for functions! You might expect that a new list is created every time when we call the function without providing an argument for the default parameter, but this is not the case: Python will create the mutable object (default parameter) only the first time the function is called, see the following code:\n",
"\n",
"(Original source: [http://docs.python-guide.org/en/latest/writing/gotchas/](http://docs.python-guide.org/en/latest/writing/gotchas/)"
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" def_list.append(value)\n",
" return def_list\n",
"\n",
"my_list = append_to_list(1)\n",
"print(my_list)\n",
"\n",
"my_other_list = append_to_list(2)\n",
"print(my_other_list)"
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57
not_so_obvious_python_stuff.ipynb
View File

@ -1,7 +1,7 @@
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"<br>\n",
"<br>\n",
"<a name='def_mutable_func></a>\n",
"## Don't use mutable objects as default arguments for functions!"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Don't use mutable objects (e.g., dictionaries, lists, sets, etc.) as default arguments for functions! You might expect that a new list is created every time when we call the function without providing an argument for the default parameter, but this is not the case: Python will create the mutable object (default parameter) only the first time the function is called, see the following code:\n",
"\n",
"(Original source: [http://docs.python-guide.org/en/latest/writing/gotchas/](http://docs.python-guide.org/en/latest/writing/gotchas/)"
]
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"def append_to_list(value, def_list=[]):\n",
" def_list.append(value)\n",
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"my_list = append_to_list(1)\n",
"print(my_list)\n",
"\n",
"my_other_list = append_to_list(2)\n",
"print(my_other_list)"
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