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02_functions/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/02_functions/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/02_functions/00_content.ipynb)."
]
},
{
@ -30,7 +30,7 @@
}
},
"source": [
"In [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#Example:-Averaging-all-even-Numbers-in-a-List), we simply typed the code to calculate the average of the even numbers in a list of whole numbers into several code cells. Then, we executed them one after another. We had no way of *reusing* the code except for either executing cells multiple times. And, whenever we find ourselves doing repetitive manual work, we can be sure that there must be a way of automating what we are doing.\n",
"In [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#Example:-Averaging-all-even-Numbers-in-a-List), we simply typed the code to calculate the average of the even numbers in a list of whole numbers into several code cells. Then, we executed them one after another. We had no way of *reusing* the code except for either executing cells multiple times. And, whenever we find ourselves doing repetitive manual work, we can be sure that there must be a way of automating what we are doing.\n",
"\n",
"This chapter shows how Python offers language constructs that let us **define** functions ourselves that we may then **call** just like the built-in ones. Also, we look at how we can extend our Python installation with functionalities written by other people."
]
@ -307,7 +307,7 @@
}
},
"source": [
"To execute a function, we **call** it with the **call operator** `()` as shown many times in [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) and above.\n",
"To execute a function, we **call** it with the **call operator** `()` as shown many times in [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) and above.\n",
"\n",
"If we are unsure whether a variable references a function or not, we can verify that with the built-in [callable() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#callable) function.\n",
"\n",
@ -538,7 +538,7 @@
}
},
"source": [
"Notice the subtle difference compared to the behavior of the `//` operator in [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##%28Arithmetic#%29-Operators) that \"rounds\" towards minus infinity: [int() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#int) always \"rounds\" towards `0`."
"Notice the subtle difference compared to the behavior of the `//` operator in [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##%28Arithmetic#%29-Operators) that \"rounds\" towards minus infinity: [int() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#int) always \"rounds\" towards `0`."
]
},
{
@ -869,7 +869,7 @@
}
},
"source": [
"We may create so-called *user-defined* **functions** with the `def` statement (cf., [reference <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/reference/compound_stmts.html#function-definitions)). To extend an already familiar example, we reuse the introductory example 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#Best-Practices) in its final Pythonic version and transform it into the function `average_evens()` below. We replace the variable name `numbers` with `integers` for didactical purposes in the first couple of examples.\n",
"We may create so-called *user-defined* **functions** with the `def` statement (cf., [reference <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/reference/compound_stmts.html#function-definitions)). To extend an already familiar example, we reuse the introductory example 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#Best-Practices) in its final Pythonic version and transform it into the function `average_evens()` below. We replace the variable name `numbers` with `integers` for didactical purposes in the first couple of examples.\n",
"\n",
"A function's **name** must be chosen according to the same naming rules as ordinary variables since Python manages function names like variables. In this book, we further adopt the convention of ending function names with parentheses `()` in text cells for faster comprehension when reading (i.e., `average_evens()` vs. `average_evens`). These are *not* part of the name but must always be written out in the `def` statement for syntactic reasons.\n",
"\n",
@ -881,7 +881,7 @@
"\n",
"A function may specify an *explicit* **return value** (i.e., \"result\" or \"output\") with the `return` statement (cf., [reference <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/reference/simple_stmts.html#the-return-statement)): Functions that have one are considered **fruitful**; otherwise, they are **void**. Functions of the latter kind are still useful because of their **side effects**. For example, the built-in [print() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#print) function changes what we see on the screen. Strictly speaking, [print() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#print) and other void functions also have an *implicit* return value, namely the `None` object.\n",
"\n",
"A function should define a **docstring** that describes what it does in a short subject line, what parameters it expects (i.e., their types), and what it returns, if anything. A docstring is a syntactically valid multi-line string (i.e., type `str`) defined within **triple-double quotes** `\"\"\"`. Strings are covered in depth in [Chapter 6 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/06_text/00_content.ipynb#The-str-Type). Widely adopted standards for docstrings are [PEP 257 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://www.python.org/dev/peps/pep-0257/) and section 3.8 of [Google's Python Style Guide <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_gh.png\">](https://github.com/google/styleguide/blob/gh-pages/pyguide.md)."
"A function should define a **docstring** that describes what it does in a short subject line, what parameters it expects (i.e., their types), and what it returns, if anything. A docstring is a syntactically valid multi-line string (i.e., type `str`) defined within **triple-double quotes** `\"\"\"`. Strings are covered in depth in [Chapter 6 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/06_text/00_content.ipynb#The-str-Type). Widely adopted standards for docstrings are [PEP 257 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://www.python.org/dev/peps/pep-0257/) and section 3.8 of [Google's Python Style Guide <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_gh.png\">](https://github.com/google/styleguide/blob/gh-pages/pyguide.md)."
]
},
{
@ -1012,7 +1012,7 @@
"source": [
"Its value may seem awkward at first: It consists of a location showing where the function is defined (i.e., `__main__` here, which is Python's way of saying \"in this notebook\") and the signature wrapped inside angle brackets `<` and `>`.\n",
" \n",
"The angle brackets are a convention to indicate that the value may *not* be used as a *literal* (i.e., typed back into another code cell). [Chapter 11 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/11_classes/00_content.ipynb) introduces the concept of a **text representation** of an object, which is related to the *semantic* meaning of an object's value as discussed in [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-/-\"Meaning\"), and the angle brackets convention is one such way to represent an object as text. When executed, the angle brackets cause a `SyntaxError` because Python expects the `<` operator to come with an operand on both sides (cf., [Chapter 3 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/03_conditionals/00_content.ipynb#Relational-Operators))."
"The angle brackets are a convention to indicate that the value may *not* be used as a *literal* (i.e., typed back into another code cell). [Chapter 11 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/11_classes/00_content.ipynb) introduces the concept of a **text representation** of an object, which is related to the *semantic* meaning of an object's value as discussed in [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-/-\"Meaning\"), and the angle brackets convention is one such way to represent an object as text. When executed, the angle brackets cause a `SyntaxError` because Python expects the `<` operator to come with an operand on both sides (cf., [Chapter 3 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/03_conditionals/00_content.ipynb#Relational-Operators))."
]
},
{
@ -1647,7 +1647,7 @@
"source": [
"[PythonTutor <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](http://pythontutor.com/visualize.html#code=numbers%20%3D%20%5B7,%2011,%208,%205,%203,%2012,%202,%206,%209,%2010,%201,%204%5D%0A%0Adef%20average_wrong%28integers%29%3A%0A%20%20%20%20evens%20%3D%20%5Bn%20for%20n%20in%20numbers%20if%20n%20%25%202%20%3D%3D%200%5D%0A%20%20%20%20average%20%3D%20sum%28evens%29%20/%20len%28evens%29%0A%20%20%20%20return%20average%0A%0Aresult%20%3D%20average_wrong%28%5B123,%20456,%20789%5D%29&cumulative=false&curstr=0&heapPrimitives=nevernest&mode=display&origin=opt-frontend.js&py=3&rawInputLstJSON=%5B%5D&textReferences=false) is again helpful at visualizing the error interactively: Creating the `list` object `evens` eventually references takes *16* computational steps, namely two for managing the list comprehension, one for setting up an empty `list` object, *twelve* for filling it with elements derived from `numbers` in the global scope (i.e., that is the error), and one to make `evens` reference it (cf., steps 6-21).\n",
"\n",
"The frames logic shown by PythonTutor is the mechanism with which Python not only manages the names inside *one* function call but also for *many* potentially *simultaneous* calls, as revealed 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#Trivial-Example:-Countdown). It is the reason why we may reuse the same names for the parameters and variables inside both `average_evens()` and `average_wrong()` without Python mixing them up. So, as we already read in the [Zen of Python <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://www.python.org/dev/peps/pep-0020/), \"namespaces are one honking great idea\" (cf., `import this`), and a frame is just a special kind of namespace."
"The frames logic shown by PythonTutor is the mechanism with which Python not only manages the names inside *one* function call but also for *many* potentially *simultaneous* calls, as revealed 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#Trivial-Example:-Countdown). It is the reason why we may reuse the same names for the parameters and variables inside both `average_evens()` and `average_wrong()` without Python mixing them up. So, as we already read in the [Zen of Python <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://www.python.org/dev/peps/pep-0020/), \"namespaces are one honking great idea\" (cf., `import this`), and a frame is just a special kind of namespace."
]
},
{
@ -2021,7 +2021,7 @@
}
},
"source": [
"So far, we have specified only one parameter in each of our user-defined functions. In [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#%28Arithmetic%29-Operators), however, we saw the built-in [divmod() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#divmod) function take two arguments. And, the order in which they are passed in matters! Whenever we call a function and list its arguments in a comma separated manner, we say that we pass in the arguments *by position* or refer to them as **positional arguments**."
"So far, we have specified only one parameter in each of our user-defined functions. In [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#%28Arithmetic%29-Operators), however, we saw the built-in [divmod() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#divmod) function take two arguments. And, the order in which they are passed in matters! Whenever we call a function and list its arguments in a comma separated manner, we say that we pass in the arguments *by position* or refer to them as **positional arguments**."
]
},
{
@ -3012,7 +3012,7 @@
"source": [
"The main point of having functions without a reference to them is to use them in a situation where we know ahead of time that we use the function only *once*.\n",
"\n",
"Popular applications of lambda expressions occur in combination with the **map-filter-reduce** paradigm (cf., [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/00_content.ipynb#Lambda-Expressions))."
"Popular applications of lambda expressions occur in combination with the **map-filter-reduce** paradigm (cf., [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/00_content.ipynb#Lambda-Expressions))."
]
}
],