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mutable objects as default arguments

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rasbt 2014-04-15 15:50:39 -04:00
parent 19e5613f57
commit 0bab1bbca1
2 changed files with 15 additions and 10 deletions
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15
.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
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@ -1,7 +1,7 @@
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@ -40,9 +40,10 @@
"- [The C3 class resolution algorithm for multiple class inheritance](#c3_class_res)\n",
"- [The behavior of += for lists](#pm_in_lists)\n",
"- [`True` and `False` in the datetime module](#datetime_module)\n",
"- [Python reuses objects for small integers](#python_small_int)\n",
"- [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)"
"- [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)"
]
},
{
@ -189,10 +190,12 @@
"<br>\n",
"<br>\n",
"<a name='python_small_int'></a>\n",
"## Python reuses objects for small integers \n",
"## Python reuses objects for small integers - always use \"==\" for equality, \"is\" for identity\n",
"\n",
"This oddity occurs, because Python tends to stores small integers as the same object, but not so for larger ones! \n",
"(*I received a comment that this is in fact a CPython artefact and must not necessarily be true in all implementations of Python!*)"
"(*I received a comment that this is in fact a CPython artefact and must not necessarily be true in all implementations of Python!*)\n",
"\n",
"So the take home message is: always use \"==\" for equality, \"is\" for identity!"
]
},
{
@ -335,7 +338,7 @@
"source": [
"<br>\n",
"<br>\n",
"<a name='def_mutable_func></a>\n",
"<a name='def_mutable_func'></a>\n",
"## Don't use mutable objects as default arguments for functions!"
]
},

10
not_so_obvious_python_stuff.ipynb
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@ -1,7 +1,7 @@
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@ -40,7 +40,7 @@
"- [The C3 class resolution algorithm for multiple class inheritance](#c3_class_res)\n",
"- [The behavior of += for lists](#pm_in_lists)\n",
"- [`True` and `False` in the datetime module](#datetime_module)\n",
"- [Python reuses objects for small integers](#python_small_int)\n",
"- [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)"
@ -190,10 +190,12 @@
"<br>\n",
"<br>\n",
"<a name='python_small_int'></a>\n",
"## Python reuses objects for small integers \n",
"## Python reuses objects for small integers - always use \"==\" for equality, \"is\" for identity\n",
"\n",
"This oddity occurs, because Python tends to stores small integers as the same object, but not so for larger ones! \n",
"(*I received a comment that this is in fact a CPython artefact and must not necessarily be true in all implementations of Python!*)"
"(*I received a comment that this is in fact a CPython artefact and must not necessarily be true in all implementations of Python!*)\n",
"\n",
"So the take home message is: always use \"==\" for equality, \"is\" for identity!"
]
},
{