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lambda update

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rasbt 2014-04-16 00:29:44 -04:00
parent 69b2774301
commit ac689dac1c
2 changed files with 27 additions and 29 deletions

29
.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb

@ -1,7 +1,7 @@
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@ -404,6 +404,10 @@
"\n", "\n",
"If both values of in a `or` expression are True, Python will select the first one, and the second one in `and` expressions\n", "If both values of in a `or` expression are True, Python will select the first one, and the second one in `and` expressions\n",
"\n", "\n",
"Or - as a reader suggested - picture it as \n",
"`a or b == a if a else b` \n",
"`a and b == b if a else a` \n",
"\n",
"(Original source: [http://gistroll.com/rolls/21/horizontal_assessments/new](http://gistroll.com/rolls/21/horizontal_assessments/new))" "(Original source: [http://gistroll.com/rolls/21/horizontal_assessments/new](http://gistroll.com/rolls/21/horizontal_assessments/new))"
] ]
}, },
@ -427,13 +431,6 @@
], ],
"prompt_number": 9 "prompt_number": 9
}, },
{
"cell_type": "markdown",
"metadata": {},
"source": [
"And a fun fact"
]
},
{ {
"cell_type": "markdown", "cell_type": "markdown",
"metadata": {}, "metadata": {},
@ -448,7 +445,7 @@
"cell_type": "markdown", "cell_type": "markdown",
"metadata": {}, "metadata": {},
"source": [ "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", "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) the first time the function is defined - not when it is called, see the following code:\n",
"\n", "\n",
"(Original source: [http://docs.python-guide.org/en/latest/writing/gotchas/](http://docs.python-guide.org/en/latest/writing/gotchas/)" "(Original source: [http://docs.python-guide.org/en/latest/writing/gotchas/](http://docs.python-guide.org/en/latest/writing/gotchas/)"
] ]
@ -599,9 +596,11 @@
"\n", "\n",
"## About lambda and closures-in-a-loop pitfall\n", "## About lambda and closures-in-a-loop pitfall\n",
"\n", "\n",
"The following example illustrates how the (last) `lambda` is being reused:\n", "Remember the [\"consuming generators\"](consuming_generators)? This example is somewhat related, but the result might still come unexpected. \n",
"\n", "\n",
"(Original source: [http://openhome.cc/eGossip/Blog/UnderstandingLambdaClosure3.html](http://openhome.cc/eGossip/Blog/UnderstandingLambdaClosure3.html))" "(Original source: [http://openhome.cc/eGossip/Blog/UnderstandingLambdaClosure3.html](http://openhome.cc/eGossip/Blog/UnderstandingLambdaClosure3.html))\n",
"\n",
"In the first example below, where we call a `lambda` function in a list comprehension, the value `i` is dereferenced every time we call `lambda` within the scope of the list comprehension. Since the list is already constructed when we `for-loop` through the list, it is set to the last value 4."
] ]
}, },
{ {
@ -627,13 +626,13 @@
] ]
} }
], ],
"prompt_number": 24 "prompt_number": 11
}, },
{ {
"cell_type": "markdown", "cell_type": "markdown",
"metadata": {}, "metadata": {},
"source": [ "source": [
"**Here, a generator can save you some pain:**" "This, however, does not apply to generators:"
] ]
}, },
{ {
@ -659,7 +658,7 @@
] ]
} }
], ],
"prompt_number": 25 "prompt_number": 9
}, },
{ {
"cell_type": "markdown", "cell_type": "markdown",
@ -985,7 +984,7 @@
"\n", "\n",
"**A. Jesse Jiryu Davis** has a nice explanation for this phenomenon (Original source: [http://emptysqua.re/blog/python-increment-is-weird-part-ii/](http://emptysqua.re/blog/python-increment-is-weird-part-ii/))\n", "**A. Jesse Jiryu Davis** has a nice explanation for this phenomenon (Original source: [http://emptysqua.re/blog/python-increment-is-weird-part-ii/](http://emptysqua.re/blog/python-increment-is-weird-part-ii/))\n",
"\n", "\n",
"If we try to extend the list via `+=` *\"then the statement executes STORE_SUBSCR, which calls the C function PyObject_SetItem, which checks if the object supports item assignment. In our case the object is a tuple, so PyObject_SetItem throws the TypeError. Mystery solved.\"*" "If we try to extend the list via `+=` *\"then the statement executes `STORE_SUBSCR`, which calls the C function `PyObject_SetItem`, which checks if the object supports item assignment. In our case the object is a tuple, so `PyObject_SetItem` throws the `TypeError`. Mystery solved.\"*"
] ]
}, },
{ {

27
not_so_obvious_python_stuff.ipynb

@ -1,7 +1,7 @@
{ {
"metadata": { "metadata": {
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"nbformat": 3, "nbformat": 3,
"nbformat_minor": 0, "nbformat_minor": 0,
@ -404,6 +404,10 @@
"\n", "\n",
"If both values of in a `or` expression are True, Python will select the first one, and the second one in `and` expressions\n", "If both values of in a `or` expression are True, Python will select the first one, and the second one in `and` expressions\n",
"\n", "\n",
"Or - as a reader suggested - picture it as \n",
"`a or b == a if a else b` \n",
"`a and b == b if a else a` \n",
"\n",
"(Original source: [http://gistroll.com/rolls/21/horizontal_assessments/new](http://gistroll.com/rolls/21/horizontal_assessments/new))" "(Original source: [http://gistroll.com/rolls/21/horizontal_assessments/new](http://gistroll.com/rolls/21/horizontal_assessments/new))"
] ]
}, },
@ -427,13 +431,6 @@
], ],
"prompt_number": 9 "prompt_number": 9
}, },
{
"cell_type": "markdown",
"metadata": {},
"source": [
"And a fun fact"
]
},
{ {
"cell_type": "markdown", "cell_type": "markdown",
"metadata": {}, "metadata": {},
@ -448,7 +445,7 @@
"cell_type": "markdown", "cell_type": "markdown",
"metadata": {}, "metadata": {},
"source": [ "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", "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) the first time the function is defined - not when it is called, see the following code:\n",
"\n", "\n",
"(Original source: [http://docs.python-guide.org/en/latest/writing/gotchas/](http://docs.python-guide.org/en/latest/writing/gotchas/)" "(Original source: [http://docs.python-guide.org/en/latest/writing/gotchas/](http://docs.python-guide.org/en/latest/writing/gotchas/)"
] ]
@ -599,9 +596,11 @@
"\n", "\n",
"## About lambda and closures-in-a-loop pitfall\n", "## About lambda and closures-in-a-loop pitfall\n",
"\n", "\n",
"The following example illustrates how the (last) `lambda` is being reused:\n", "Remember the [\"consuming generators\"](consuming_generators)? This example is somewhat related, but the result might still come unexpected. \n",
"\n", "\n",
"(Original source: [http://openhome.cc/eGossip/Blog/UnderstandingLambdaClosure3.html](http://openhome.cc/eGossip/Blog/UnderstandingLambdaClosure3.html))" "(Original source: [http://openhome.cc/eGossip/Blog/UnderstandingLambdaClosure3.html](http://openhome.cc/eGossip/Blog/UnderstandingLambdaClosure3.html))\n",
"\n",
"In the first example below, where we call a `lambda` function in a list comprehension, the value `i` is dereferenced every time we call `lambda` within the scope of the list comprehension. Since the list is already constructed when we `for-loop` through the list, it is set to the last value 4."
] ]
}, },
{ {
@ -627,13 +626,13 @@
] ]
} }
], ],
"prompt_number": 24 "prompt_number": 11
}, },
{ {
"cell_type": "markdown", "cell_type": "markdown",
"metadata": {}, "metadata": {},
"source": [ "source": [
"**Here, a generator can save you some pain:**" "This, however, does not apply to generators:"
] ]
}, },
{ {
@ -659,7 +658,7 @@
] ]
} }
], ],
"prompt_number": 25 "prompt_number": 9
}, },
{ {
"cell_type": "markdown", "cell_type": "markdown",