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14
09_mappings/00_content.ipynb
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@ -8,7 +8,7 @@
}
},
"source": [
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Clear All Outputs*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *before* reading this notebook to reset its output. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/develop?urlpath=lab/tree/09_mappings/00_content.ipynb)."
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Clear All Outputs*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *before* reading this notebook to reset its output. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/main?urlpath=lab/tree/09_mappings/00_content.ipynb)."
]
},
{
@ -30,7 +30,7 @@
}
},
"source": [
"While [Chapter 7 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/07_sequences/00_content.ipynb) focuses on one special kind of *collection* types, namely *sequences*, this chapter introduces two more kinds: **Mappings** and **sets**. Both are presented in this chapter as they share the *same* underlying implementation.\n",
"While [Chapter 7 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/07_sequences/00_content.ipynb) focuses on one special kind of *collection* types, namely *sequences*, this chapter introduces two more kinds: **Mappings** and **sets**. Both are presented in this chapter as they share the *same* underlying implementation.\n",
"\n",
"The `dict` type (cf, [documentation <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/stdtypes.html#dict)) introduced in the next section is an essential part in a data scientist's toolbox for two reasons: First, Python employs `dict` objects basically everywhere internally. Second, after the many concepts involving *sequential* data, *mappings* provide a different perspective on data and enhance our general problem solving skills."
]
@ -56,7 +56,7 @@
"source": [
"A *mapping* is a one-to-one correspondence from a set of **keys** to a set of **values**. In other words, a *mapping* is a *collection* of **key-value pairs**, also called **items** for short.\n",
"\n",
"In the context of mappings, the term *value* has a meaning different from the *value* every object has: In the \"bag\" analogy from [Chapter 1 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/01_elements/00_content.ipynb#Value-/-%28Semantic%29-\"Meaning\"), we describe an object's value to be the semantic meaning of the $0$s and $1$s it contains. Here, the terms *key* and *value* mean the *role* an object takes within a mapping. Both, *keys* and *values*, are *objects* on their own with distinct *values*.\n",
"In the context of mappings, the term *value* has a meaning different from the *value* every object has: In the \"bag\" analogy from [Chapter 1 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/01_elements/00_content.ipynb#Value-/-%28Semantic%29-\"Meaning\"), we describe an object's value to be the semantic meaning of the $0$s and $1$s it contains. Here, the terms *key* and *value* mean the *role* an object takes within a mapping. Both, *keys* and *values*, are *objects* on their own with distinct *values*.\n",
"\n",
"Let's continue with an example. To create a `dict` object, we commonly use the literal notation, `{..: .., ..: .., ...}`, and list all the items. `to_words` below maps the `int` objects `0`, `1`, and `2` to their English word equivalents, `\"zero\"`, `\"one\"`, and `\"two\"`, and `from_words` does the opposite. A stylistic side note: Pythonistas often expand `dict` or `list` definitions by writing each item or element on a line on their own. Also, the commas `,` after the respective *last* items, `2: \"two\"` and `\"two\": 2`, are *not* a mistake although they *may* be left out. Besides easier reading, such a style has technical advantages that we do not go into detail about here (cf., [source <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://www.python.org/dev/peps/pep-0008/#when-to-use-trailing-commas))."
]
@ -550,7 +550,7 @@
}
},
"source": [
"In [Chapter 0 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/00_intro/00_content.ipynb#Isn't-C-a-lot-faster?), we argue that a major advantage of using Python is that it takes care of the memory managment for us. In line with that, we have never talked about the C level implementation thus far in the book. However, the `dict` type, among others, exhibits some behaviors that may seem \"weird\" for a beginner. To build some intuition, we describe the underlying implementation details on a conceptual level.\n",
"In [Chapter 0 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/00_intro/00_content.ipynb#Isn't-C-a-lot-faster?), we argue that a major advantage of using Python is that it takes care of the memory managment for us. In line with that, we have never talked about the C level implementation thus far in the book. However, the `dict` type, among others, exhibits some behaviors that may seem \"weird\" for a beginner. To build some intuition, we describe the underlying implementation details on a conceptual level.\n",
"\n",
"The first unintuitive behavior is that we may *not* use a *mutable* object as a key. That results in a `TypeError`."
]
@ -1176,7 +1176,7 @@
}
},
"source": [
"In [Chapter 7 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/07_sequences/00_content.ipynb#Collections-vs.-Sequences), we see how a *sequence* is a special kind of a *collection*, and that collections can be described as\n",
"In [Chapter 7 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/07_sequences/00_content.ipynb#Collections-vs.-Sequences), we see how a *sequence* is a special kind of a *collection*, and that collections can be described as\n",
"- *iterable*\n",
"- *containers*\n",
"- with a *finite* number of elements.\n",
@ -1245,7 +1245,7 @@
"Also, `dict` objects may be looped over, for example, with the `for` statement. So, in the terminology of the [collections.abc <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/collections.abc.html) module, they are `Iterable` objects.\n",
"\n",
"Regarding the *iteration order* things are not that easy, and programmers seem to often be confused about this (e.g., this [discussion](https://stackoverflow.com/questions/58413076/why-are-python-dictionaries-not-reversible-for-python3-7)). The confusion usually comes from one of two reasons:\n",
"1. The internal implementation of the `dict` type has been changed over the last couple of minor release versions, and the communication thereof in the official release notes was done only in a later version. In a nutshell, before Python 3.6, the core developers did not care about the iteration order at all as the goal was to optimize `dict` objects for computational speed, primarily regarding key look-up (cf., the \"Indexing -> Key Look-up\" section below). That meant that looping over the *same* `dict` object several times during its lifetime could have resulted in *different* iteration orders. In Python 3.6, it was discovered that it is possible to make `dict` objects remember the order in that items have been inserted *without* giving up any computational speed or memory (cf., [Raymond Hettinger](https://github.com/rhettinger)'s talk in the [Further Resources <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/08_resources.ipynb#History-of-the-dict-Type) section at the end of the chapter. However, that change was kept an *implementation detail* and *not* made official in the release notes. That was then done in Python 3.7's release notes (cf., [Python 3.7 release notes <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://www.python.org/downloads/release/python-370/)).\n",
"1. The internal implementation of the `dict` type has been changed over the last couple of minor release versions, and the communication thereof in the official release notes was done only in a later version. In a nutshell, before Python 3.6, the core developers did not care about the iteration order at all as the goal was to optimize `dict` objects for computational speed, primarily regarding key look-up (cf., the \"Indexing -> Key Look-up\" section below). That meant that looping over the *same* `dict` object several times during its lifetime could have resulted in *different* iteration orders. In Python 3.6, it was discovered that it is possible to make `dict` objects remember the order in that items have been inserted *without* giving up any computational speed or memory (cf., [Raymond Hettinger](https://github.com/rhettinger)'s talk in the [Further Resources <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/08_resources.ipynb#History-of-the-dict-Type) section at the end of the chapter. However, that change was kept an *implementation detail* and *not* made official in the release notes. That was then done in Python 3.7's release notes (cf., [Python 3.7 release notes <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://www.python.org/downloads/release/python-370/)).\n",
"2. To make order an official part of a data type, it must adhere to the `Reversible` ABC in the [collections.abc <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/collections.abc.html) module and support the [reversed() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#reversed) built-in. Even though the items' order inside a `dict` is remembered for Python 3.6 and 3.7, `dict` objects are *not* `Reversible`. That was then changed in Python 3.8, but again *not* officially communicated (cf., [Python 3.8 release notes](https://www.python.org/downloads/release/python-380/)).\n",
"\n",
"In summary, we can say that depending on the exact Python version a `dict` object *may* remember the **insertion order** of its items.\n",
@ -3541,7 +3541,7 @@
}
},
"source": [
"Analogous to `list` comprehensions in [Chapter 8 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/08_mfr/01_content.ipynb#list-Comprehensions), `dict` comprehensions are a concise literal notation to derive new `dict` objects out of existing ones.\n",
"Analogous to `list` comprehensions in [Chapter 8 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/08_mfr/01_content.ipynb#list-Comprehensions), `dict` comprehensions are a concise literal notation to derive new `dict` objects out of existing ones.\n",
"\n",
"For example, let's derive `from_words` out of `to_words` below by swapping the keys and values."
]

4
09_mappings/01_exercises_nested-data.ipynb
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@ -4,7 +4,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Run All*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *after* finishing the exercises to ensure that your solution runs top to bottom *without* any errors. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/develop?urlpath=lab/tree/09_mappings/01_exercises.ipynb)."
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Run All*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *after* finishing the exercises to ensure that your solution runs top to bottom *without* any errors. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/main?urlpath=lab/tree/09_mappings/01_exercises.ipynb)."
]
},
{
@ -18,7 +18,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"The exercises below assume that you have read the [first part <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/00_content.ipynb) of Chapter 9.\n",
"The exercises below assume that you have read the [first part <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/00_content.ipynb) of Chapter 9.\n",
"\n",
"The `...`'s in the code cells indicate where you need to fill in code snippets. The number of `...`'s within a code cell give you a rough idea of how many lines of code are needed to solve the task. You should not need to create any additional code cells for your final solution. However, you may want to use temporary code cells to try out some ideas."
]

10
09_mappings/02_content.ipynb
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@ -8,7 +8,7 @@
}
},
"source": [
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Clear All Outputs*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *before* reading this notebook to reset its output. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/develop?urlpath=lab/tree/09_mappings/02_content.ipynb)."
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Clear All Outputs*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *before* reading this notebook to reset its output. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/main?urlpath=lab/tree/09_mappings/02_content.ipynb)."
]
},
{
@ -30,7 +30,7 @@
}
},
"source": [
"After introducing the `dict` type in the [first part <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/00_content.ipynb) of this chapter, we first look at an extension of the packing and unpacking syntax that involves `dict` objects. Then, we see how mappings can help us write computationally more efficient implementations to recursive solutions of problems as introduced in [Chapter 4 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/04_iteration/00_content.ipynb#Recursion). In a way, this second part of the chapter \"finishes\" Chapter 4."
"After introducing the `dict` type in the [first part <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/00_content.ipynb) of this chapter, we first look at an extension of the packing and unpacking syntax that involves `dict` objects. Then, we see how mappings can help us write computationally more efficient implementations to recursive solutions of problems as introduced in [Chapter 4 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/04_iteration/00_content.ipynb#Recursion). In a way, this second part of the chapter \"finishes\" Chapter 4."
]
},
{
@ -52,7 +52,7 @@
}
},
"source": [
"Just as a single `*` symbol is used for packing and unpacking iterables in [Chapter 7 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/07_sequences/03_content.ipynb#Packing-&-Unpacking), a double `**` symbol implements packing and unpacking for mappings.\n",
"Just as a single `*` symbol is used for packing and unpacking iterables in [Chapter 7 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/07_sequences/03_content.ipynb#Packing-&-Unpacking), a double `**` symbol implements packing and unpacking for mappings.\n",
"\n",
"Let's say we have `to_words` and `more_words` as below and want to merge the items together into a *new* `dict` object."
]
@ -608,7 +608,7 @@
}
},
"source": [
"The *recursive* implementation of the [Fibonacci numbers <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_wiki.png\">](https://en.wikipedia.org/wiki/Fibonacci_number) in [Chapter 4 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/04_iteration/00_content.ipynb#\"Easy-at-first-Glance\"-Example:-Fibonacci-Numbers) takes long to compute for large Fibonacci numbers. For easier comparison, we show the old `fibonacci()` version here again."
"The *recursive* implementation of the [Fibonacci numbers <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_wiki.png\">](https://en.wikipedia.org/wiki/Fibonacci_number) in [Chapter 4 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/04_iteration/00_content.ipynb#\"Easy-at-first-Glance\"-Example:-Fibonacci-Numbers) takes long to compute for large Fibonacci numbers. For easier comparison, we show the old `fibonacci()` version here again."
]
},
{
@ -831,7 +831,7 @@
}
},
"source": [
"When we follow the flow of execution closely, we realize that the intermediate results represented by the left-most path in the graph above are calculated first. `fibonacci(1)`, the left-most leaf node $F(1)$, is the first base case reached, followed immediately by `fibonacci(0)`. From that moment onwards, the flow of execution moves back up the left-most path while adding together the two corresponding child nodes. Effectively, this mirrors the *iterative* implementation in that the order of all computational steps are *identical* (cf., the \"*Hard at first Glance*\" example in [Chapter 4 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/04_iteration/02_content.ipynb#\"Hard-at-first-Glance\"-Example:-Fibonacci-Numbers--(revisited))).\n",
"When we follow the flow of execution closely, we realize that the intermediate results represented by the left-most path in the graph above are calculated first. `fibonacci(1)`, the left-most leaf node $F(1)$, is the first base case reached, followed immediately by `fibonacci(0)`. From that moment onwards, the flow of execution moves back up the left-most path while adding together the two corresponding child nodes. Effectively, this mirrors the *iterative* implementation in that the order of all computational steps are *identical* (cf., the \"*Hard at first Glance*\" example in [Chapter 4 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/04_iteration/02_content.ipynb#\"Hard-at-first-Glance\"-Example:-Fibonacci-Numbers--(revisited))).\n",
"\n",
"We added a keyword-only argument `debug` that allows the caller to print out a message every time a `i` was *not* in the `memo`."
]

8
09_mappings/03_exercises_fibonacci.ipynb
View file

@ -4,7 +4,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Run All*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *after* finishing the exercises to ensure that your solution runs top to bottom *without* any errors. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/develop?urlpath=lab/tree/09_mappings/03_exercises.ipynb)."
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Run All*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *after* finishing the exercises to ensure that your solution runs top to bottom *without* any errors. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/main?urlpath=lab/tree/09_mappings/03_exercises.ipynb)."
]
},
{
@ -18,7 +18,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"The exercises below assume that you have read the [second part <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/02_content.ipynb) of Chapter 9.\n",
"The exercises below assume that you have read the [second part <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/02_content.ipynb) of Chapter 9.\n",
"\n",
"The `...`'s in the code cells indicate where you need to fill in code snippets. The number of `...`'s within a code cell give you a rough idea of how many lines of code are needed to solve the task. You should not need to create any additional code cells for your final solution. However, you may want to use temporary code cells to try out some ideas."
]
@ -38,7 +38,7 @@
}
},
"source": [
"It is considered *bad practice* to make a function and thereby its correctness dependent on a program's *global state*: For example, in the \"*Easy at second Glance: Fibonacci Numbers*\" section in [Chapter 9 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/02_content.ipynb#\"Easy-at-second-Glance\"-Example:-Fibonacci-Numbers--%28revisited%29), we use a global `memo` to store the Fibonacci numbers that have already been calculated.\n",
"It is considered *bad practice* to make a function and thereby its correctness dependent on a program's *global state*: For example, in the \"*Easy at second Glance: Fibonacci Numbers*\" section in [Chapter 9 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/02_content.ipynb#\"Easy-at-second-Glance\"-Example:-Fibonacci-Numbers--%28revisited%29), we use a global `memo` to store the Fibonacci numbers that have already been calculated.\n",
"\n",
"That `memo` dictionary could be \"manipulated.\" More often than not, such things happen by accident: Imagine we wrote two independent recursive functions that both rely on memoization to solve different problems, and, unintentionally, we made both work with the *same* global `memo`. As a result, we would observe \"random\" bugs depending on the order in which we executed these functions. Such bugs are hard to track down in practice.\n",
"\n",
@ -185,7 +185,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"The runtime of `fibonacci()` is now stable: There is no message that \"an intermediate result is being cached\" as in [Chapter 9 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/02_content.ipynb#\"Easy-at-second-Glance\"-Example:-Fibonacci-Numbers--%28revisited%29).\n",
"The runtime of `fibonacci()` is now stable: There is no message that \"an intermediate result is being cached\" as in [Chapter 9 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/02_content.ipynb#\"Easy-at-second-Glance\"-Example:-Fibonacci-Numbers--%28revisited%29).\n",
"\n",
"**Q7**: Execute the following code cells a couple of times to observe that!"
]

4
09_mappings/04_content.ipynb
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@ -8,7 +8,7 @@
}
},
"source": [
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Clear All Outputs*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *before* reading this notebook to reset its output. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/develop?urlpath=lab/tree/09_mappings/04_content.ipynb)."
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Clear All Outputs*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *before* reading this notebook to reset its output. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/main?urlpath=lab/tree/09_mappings/04_content.ipynb)."
]
},
{
@ -1407,7 +1407,7 @@
}
},
"source": [
"Python provides a literal notation for `set` comprehensions that works exactly like the one for `dict` comprehensions described in the [first part <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/00_content.ipynb#dict-Comprehensions) of this chapter except that they use a single loop variable instead of a key-value pair.\n",
"Python provides a literal notation for `set` comprehensions that works exactly like the one for `dict` comprehensions described in the [first part <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/00_content.ipynb#dict-Comprehensions) of this chapter except that they use a single loop variable instead of a key-value pair.\n",
"\n",
"For example, let's create a new `set` object that consists of the squares of all the elements of `numbers`."
]

2
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@ -8,7 +8,7 @@
}
},
"source": [
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Clear All Outputs*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *before* reading this notebook to reset its output. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/develop?urlpath=lab/tree/09_mappings/05_appendix.ipynb)."
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Clear All Outputs*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *before* reading this notebook to reset its output. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/main?urlpath=lab/tree/09_mappings/05_appendix.ipynb)."
]
},
{

4
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@ -11,7 +11,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"The questions below assume that you have read the [first <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/00_content.ipynb), [second <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/02_content.ipynb), and [third <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/04_content.ipynb) part of Chapter 9.\n",
"The questions below assume that you have read the [first <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/00_content.ipynb), [second <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/02_content.ipynb), and [third <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/04_content.ipynb) part of Chapter 9.\n",
"\n",
"Be concise in your answers! Most questions can be answered in *one* sentence."
]
@ -99,7 +99,7 @@
"source": [
"**Q6**: **Memoization** is an essential concept to know to solve problems in the real world. Together with the idea of **recursion**, it enables us to solve problems in a \"backwards\" fashion *effectively*.\n",
"\n",
"Compare the **recursive** formulation of `fibonacci()` in [Chapter 9 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/09_mappings/02_content.ipynb#\"Easy-at-second-Glance\"-Example:-Fibonacci-Numbers--(revisited)), the \"*Easy at second Glance*\" example, with the **iterative** version in [Chapter 4 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/04_iteration/02_content.ipynb#\"Hard-at-first-Glance\"-Example:-Fibonacci-Numbers-%28revisited%29), the \"*Hard at first Glance*\" example!\n",
"Compare the **recursive** formulation of `fibonacci()` in [Chapter 9 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/09_mappings/02_content.ipynb#\"Easy-at-second-Glance\"-Example:-Fibonacci-Numbers--(revisited)), the \"*Easy at second Glance*\" example, with the **iterative** version in [Chapter 4 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/04_iteration/02_content.ipynb#\"Hard-at-first-Glance\"-Example:-Fibonacci-Numbers-%28revisited%29), the \"*Hard at first Glance*\" example!\n",
"\n",
"How are they similar and how do they differ? Also consider how the flow of execution behaves when the functions are being executed."
]

2
09_mappings/08_resources.ipynb
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@ -4,7 +4,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Clear All Outputs*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *before* reading this notebook to reset its output. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/develop?urlpath=lab/tree/09_mappings/08_resources.ipynb)."
"**Note**: Click on \"*Kernel*\" > \"*Restart Kernel and Clear All Outputs*\" in [JupyterLab](https://jupyterlab.readthedocs.io/en/stable/) *before* reading this notebook to reset its output. If you cannot run this file on your machine, you may want to open it [in the cloud <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_mb.png\">](https://mybinder.org/v2/gh/webartifex/intro-to-python/main?urlpath=lab/tree/09_mappings/08_resources.ipynb)."
]
},
{