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06_text/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/06_text/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/06_text/00_content.ipynb)."
]
},
{
@ -30,7 +30,7 @@
}
},
"source": [
"In this chapter, we continue the study of the built-in data types. The next layer on top of numbers consists of **textual data** that are modeled primarily with the `str` type in Python. `str` objects are more complex than the numeric objects in [Chapter 5 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/05_numbers/00_content.ipynb) as they *consist* of an *arbitrary* and possibly large number of *individual* characters that may be chosen from *any* alphabet in the history of humankind. Luckily, Python abstracts away most of this complexity from us. However, after looking at the `str` type in great detail, we briefly introduce the `bytes` type at the end of this chapter to understand how characters are modeled in memory."
"In this chapter, we continue the study of the built-in data types. The next layer on top of numbers consists of **textual data** that are modeled primarily with the `str` type in Python. `str` objects are more complex than the numeric objects in [Chapter 5 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/05_numbers/00_content.ipynb) as they *consist* of an *arbitrary* and possibly large number of *individual* characters that may be chosen from *any* alphabet in the history of humankind. Luckily, Python abstracts away most of this complexity from us. However, after looking at the `str` type in great detail, we briefly introduce the `bytes` type at the end of this chapter to understand how characters are modeled in memory."
]
},
{
@ -137,7 +137,7 @@
"source": [
"As seen before, a `str` object evaluates to itself in a literal notation with enclosing **single quotes** `'`.\n",
"\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/develop/01_elements/00_content.ipynb#Value-/-(Semantic)-\"Meaning\"), we specify the double quotes `\"` convention this book follows. Yet, single quotes `'` and double quotes `\"` are *perfect* substitutes. We could use the reverse convention, as well. As [this discussion <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_so.png\">](https://stackoverflow.com/questions/56011/single-quotes-vs-double-quotes-in-python) shows, many programmers have *strong* opinions about such conventions. Consequently, the discussion was \"closed as not constructive\" by the moderators."
"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-/-(Semantic)-\"Meaning\"), we specify the double quotes `\"` convention this book follows. Yet, single quotes `'` and double quotes `\"` are *perfect* substitutes. We could use the reverse convention, as well. As [this discussion <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_so.png\">](https://stackoverflow.com/questions/56011/single-quotes-vs-double-quotes-in-python) shows, many programmers have *strong* opinions about such conventions. Consequently, the discussion was \"closed as not constructive\" by the moderators."
]
},
{
@ -290,7 +290,7 @@
}
},
"source": [
"As an alternative to the literal notation, we may use the built-in [str() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/stdtypes.html#str) constructor to cast non-`str` objects as `str` ones. As [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) reveals, basically any object in Python has a **text representation**. Because of that we may also pass `list` objects, the boolean `True` and `False`, or `None` to [str() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/stdtypes.html#str)."
"As an alternative to the literal notation, we may use the built-in [str() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/stdtypes.html#str) constructor to cast non-`str` objects as `str` ones. As [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) reveals, basically any object in Python has a **text representation**. Because of that we may also pass `list` objects, the boolean `True` and `False`, or `None` to [str() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/stdtypes.html#str)."
]
},
{
@ -456,7 +456,7 @@
}
},
"source": [
"As shown in the \"*Guessing a Coin Toss*\" 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/03_content.ipynb#Example:-Guessing-a-Coin-Toss), the built-in [input() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#input) function displays a prompt to the user and returns whatever is entered as a `str` object. [input() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#input) is in particular valuable when writing command-line tools."
"As shown in the \"*Guessing a Coin Toss*\" 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/03_content.ipynb#Example:-Guessing-a-Coin-Toss), the built-in [input() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#input) function displays a prompt to the user and returns whatever is entered as a `str` object. [input() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#input) is in particular valuable when writing command-line tools."
]
},
{
@ -571,7 +571,7 @@
}
},
"source": [
"[open() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#open) returns a **[proxy <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_wiki.png\">](https://en.wikipedia.org/wiki/Proxy_pattern)** object of type `TextIOWrapper` that allows us to interact with the file on disk. `mode='r'` shows that we opened the file in read-only mode and `encoding='UTF-8'` is explained in detail in the [The `bytes` Type <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/01_content.ipynb#The-bytes-Type) section at the end of this chapter."
"[open() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#open) returns a **[proxy <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_wiki.png\">](https://en.wikipedia.org/wiki/Proxy_pattern)** object of type `TextIOWrapper` that allows us to interact with the file on disk. `mode='r'` shows that we opened the file in read-only mode and `encoding='UTF-8'` is explained in detail in the [The `bytes` Type <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/01_content.ipynb#The-bytes-Type) section at the end of this chapter."
]
},
{
@ -1010,7 +1010,7 @@
}
},
"source": [
"Using syntax familiar from [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#The-try-Statement) to explain what the `with open(...) as file:` does above, we provide an alternative formulation with a `try` statement below: The `finally`-branch is *always* executed, even if an exception is raised inside the `for`-loop. Therefore, `file` is sure to be closed too. However, this formulation is somewhat less expressive."
"Using syntax familiar from [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#The-try-Statement) to explain what the `with open(...) as file:` does above, we provide an alternative formulation with a `try` statement below: The `finally`-branch is *always* executed, even if an exception is raised inside the `for`-loop. Therefore, `file` is sure to be closed too. However, this formulation is somewhat less expressive."
]
},
{
@ -1373,7 +1373,7 @@
}
},
"source": [
"A **sequence** is yet another *abstract* concept (cf., the \"*Containers vs. Iterables*\" section 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#Containers-vs.-Iterables)).\n",
"A **sequence** is yet another *abstract* concept (cf., the \"*Containers vs. Iterables*\" section 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#Containers-vs.-Iterables)).\n",
"\n",
"It unifies *four* [orthogonal <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_wiki.png\">](https://en.wikipedia.org/wiki/Orthogonality) (i.e., \"independent\") concepts into one bigger idea: Any data type, such as `str`, is considered a sequence if it\n",
"\n",
@ -1382,11 +1382,11 @@
"3. can be **iterated** over\n",
"4. in a *predictable* **order**.\n",
"\n",
"[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) formalizes these concepts in great detail. Here, we keep our focus on the `str` type that historically received its name as it models a **[string of characters <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_wiki.png\">](https://en.wikipedia.org/wiki/String_%28computer_science%29)**. *String* is simply another term for *sequence* in the computer science literature.\n",
"[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) formalizes these concepts in great detail. Here, we keep our focus on the `str` type that historically received its name as it models a **[string of characters <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_wiki.png\">](https://en.wikipedia.org/wiki/String_%28computer_science%29)**. *String* is simply another term for *sequence* in the computer science literature.\n",
"\n",
"Another example of a sequence is the `list` type. Because of that, `str` objects may be treated like `list` objects in many situations.\n",
"\n",
"Below, the built-in [len() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#len) function tells us how many characters make up `text`. [len() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#len) would not work with an \"infinite\" object. As anything modeled in a program must fit into a computer's finite memory, there cannot exist truly infinite objects; however, [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#Iterators-vs.-Iterables) introduces specialized iterable data types that can be used to model an *infinite* series of \"things\" and that, consequently, have no concept of \"length.\""
"Below, the built-in [len() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#len) function tells us how many characters make up `text`. [len() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#len) would not work with an \"infinite\" object. As anything modeled in a program must fit into a computer's finite memory, there cannot exist truly infinite objects; however, [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#Iterators-vs.-Iterables) introduces specialized iterable data types that can be used to model an *infinite* series of \"things\" and that, consequently, have no concept of \"length.\""
]
},
{
@ -1605,7 +1605,7 @@
}
},
"source": [
"As `str` objects are *ordered* and *finite*, we may **index** into them to obtain individual characters with the **indexing operator** `[]`. This is analogous to how we obtained individual elements of a `list` object 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/03_content.ipynb#Who-am-I?-And-how-many?)."
"As `str` objects are *ordered* and *finite*, we may **index** into them to obtain individual characters with the **indexing operator** `[]`. This is analogous to how we obtained individual elements of a `list` object 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/03_content.ipynb#Who-am-I?-And-how-many?)."
]
},
{
@ -2292,9 +2292,9 @@
}
},
"source": [
"Whereas elements of a `list` object *may* be *re-assigned*, as shortly hinted at 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/03_content.ipynb#Who-am-I?-And-how-many?), this is *not* allowed for the individual characters of `str` objects. Once created, they can *not* be changed. Formally, we say that `str` objects are **immutable**. In that regard, they are like the numeric types in [Chapter 5 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/05_numbers/00_content.ipynb).\n",
"Whereas elements of a `list` object *may* be *re-assigned*, as shortly hinted at 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/03_content.ipynb#Who-am-I?-And-how-many?), this is *not* allowed for the individual characters of `str` objects. Once created, they can *not* be changed. Formally, we say that `str` objects are **immutable**. In that regard, they are like the numeric types in [Chapter 5 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/main/05_numbers/00_content.ipynb).\n",
"\n",
"On the contrary, objects that may be changed after creation, are called **mutable**. We already saw 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/03_content.ipynb#Who-am-I?-And-how-many?) how mutable objects are more difficult to reason about for a beginner, in particular, if more than one variable references it. Yet, mutability does have its place in a programmer's toolbox, and we revisit this idea in the next chapters.\n",
"On the contrary, objects that may be changed after creation, are called **mutable**. We already saw 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/03_content.ipynb#Who-am-I?-And-how-many?) how mutable objects are more difficult to reason about for a beginner, in particular, if more than one variable references it. Yet, mutability does have its place in a programmer's toolbox, and we revisit this idea in the next chapters.\n",
"\n",
"The `TypeError` indicates that `str` objects are *immutable*: Assignment to an index or a slice are *not* supported."
]
@ -3377,7 +3377,7 @@
}
},
"source": [
"As mentioned 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#Operator-Overloading), the `+` and `*` operators are *overloaded* and used for **string concatenation**. They always create *new* `str` objects. That has nothing to do with the `str` type's immutability, but is the default behavior of operators."
"As mentioned 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#Operator-Overloading), the `+` and `*` operators are *overloaded* and used for **string concatenation**. They always create *new* `str` objects. That has nothing to do with the `str` type's immutability, but is the default behavior of operators."
]
},
{
@ -3447,7 +3447,7 @@
}
},
"source": [
"The *relational* operators also work with `str` objects, another example of operator overloading. Comparison is done one character at a time in a pairwise fashion until the first pair differs or one operand ends. However, `str` objects are sorted in a \"weird\" way. For example, all upper case characters come before all lower case characters. The reason for that is given in the \"*Characters are Numbers with a Convention*\" sub-section in 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/06_text/02_content.ipynb#Characters-are-Numbers-with-a-Convention) of this chapter."
"The *relational* operators also work with `str` objects, another example of operator overloading. Comparison is done one character at a time in a pairwise fashion until the first pair differs or one operand ends. However, `str` objects are sorted in a \"weird\" way. For example, all upper case characters come before all lower case characters. The reason for that is given in the \"*Characters are Numbers with a Convention*\" sub-section in 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/06_text/02_content.ipynb#Characters-are-Numbers-with-a-Convention) of this chapter."
]
},
{
@ -3857,7 +3857,7 @@
}
},
"source": [
"The `%` operator that we saw in the context of modulo division 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) is overloaded with string interpolation when its first operand is a `str` object. The second operand consists of all expressions to be filled in. Format specifiers work with a `%` instead of curly braces and according to a different set of rules referred to as **[printf-style string formatting <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting)**. So, `{:.2f}` becomes `%.2f`.\n",
"The `%` operator that we saw in the context of modulo division 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) is overloaded with string interpolation when its first operand is a `str` object. The second operand consists of all expressions to be filled in. Format specifiers work with a `%` instead of curly braces and according to a different set of rules referred to as **[printf-style string formatting <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting)**. So, `{:.2f}` becomes `%.2f`.\n",
"\n",
"This way of string interpolation is the oldest and originates from the [C language <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_wiki.png\">](https://en.wikipedia.org/wiki/C_%28programming_language%29). It is still widely spread, but we should use one of the other two ways instead. We show it here mainly for completeness sake."
]
@ -3894,7 +3894,7 @@
}
},
"source": [
"To insert more than one expression, we must list them in order and between parenthesis `(` and `)`. As [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#The-tuple-Type) reveals, this literal syntax creates an object of type `tuple`. Also, to format an expression as text, we use the format specifier `%s`."
"To insert more than one expression, we must list them in order and between parenthesis `(` and `)`. As [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#The-tuple-Type) reveals, this literal syntax creates an object of type `tuple`. Also, to format an expression as text, we use the format specifier `%s`."
]
},
{