Text Processing
===============


Regex
-----

https://docs.python.org/3/library/re.html#regular-expression-syntax

find all instances of a single match - All adverbs

.. code-block:: python

    import re

    s = "I am fully, and totally confident that" \
    "programming and developing software is completely my thing"
    adverbs = re.findall(r"\w{2,}ly", s)
    print(adverbs)

``re.search()`` matches the first occurrence of a pattern in a string

find the first pattern match from the beginning of the string, so the second email before is never found

?? for non-greedy matching

.. code-block:: python

    import re

    s = "my work email is mk@plataux.com, and that is my work email, mk.mahfouz@gmail.com"

    m = re.search(r"(\w+)@(\w+\.\w+)", s)

    # the two matched groups in parentheses
    print("sub-groups: ", m.groups())
    print("email: ", m.group())
    print("user: ", m.group(1))
    print("domain: ", m.group(2))

``re.match()`` find the first pattern match from the beginning of the string
Multi-group capturing can be used

.. code-block:: python

    s = "781-521-4520 is my phone number"
    m = re.match(r"^(\d{3,4}[-\s]??){3}", s)
    print(m.group())

    # We can also match a phone number in three groups
    m = re.match(r"^(\d{3})([-\s])(\d{3})\2(\d{4})", s)

    print(m.groups())


Use group capturing Grab keys and values from a single level JSON string using match groups

.. code-block:: python

    import re

    s = """{
      "a": "apples",
      "b": "berries","c": "cherries",
      "pi": 3.14,
      "x": "Xenon"
    }"""

    m = re.findall(r'\"(\w+)\":\s*(\"?)([\w\d.]+)\2', s)
    d = {mx[0]: mx[2] if mx[1] else float(mx[2]) for mx in m}
    print(d)


Text Formatting
---------------

Format Specification Mini-Language
https://docs.python.org/3/library/string.html#formatstrings

.. code-block::

    format_spec     ::=  [[fill]align][sign][#][0][width][grouping_option][.precision][type]
    fill            ::=  <any character>
    align           ::=  "<" | ">" | "=" | "^"
    sign            ::=  "+" | "-" | " "
    width           ::=  digit+
    grouping_option ::=  "_" | ","
    precision       ::=  digit+
    type            ::=  "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"


Text formatting can be done with several constructs

* ``format(value, fmt_str)`` builtin function. It can only one value and format it
* ``"{}, {}, {}".format(1, 2, 3)`` the ``str.format(*vars)`` function that can format multiple arguments
* ``f"{x}, {y}, {z}"`` modern f-strings
* ``"%d, %d, %d" % (2,4,8)`` old-style (C-style) format strings with modulo iterable parameters


Floating Number Formatting
**************************

.. code-block:: python

    print(f"{2345.491:_^-20,.2f}")
    # or
    print(format(2345.491,"_^-20,.2f"))


This format spec breakdown

* ``_`` underscore padded
* ``^`` Centered within the given width
* ``-`` means sign only appears for negative numbers
* ``20`` the total width of the string
* ``,`` the separator to be a comma
* ``.2`` precision
* ``f`` the type of the value


.. code-block:: python

    # the speed of light in km/sec
    format(3 * 10**8, ".3E")

This format spec breakdown

* ``.3`` decimal places precision
* ``E`` scientific notation with a capital E


Integer Formatting
******************

.. code-block:: python

    format(1020, "b")
    format(1020, "X")

* ``b`` for binary representation
* ``X`` for Hexadecimal representation, with Capital Letters


Datetime Formatting
*******************

https://docs.python.org/3/library/datetime.html#strftime-and-strptime-format-codes

.. code-block:: python

    import datetime as dtx
    from zoneinfo import ZoneInfo

    now = dtx.datetime.now()
    print(format(now, '%A'))
    print(f"{now:%A %d-%m-%Y}")


    now = dtx.datetime.now(tz=ZoneInfo("localtime"))

    print("right now it is weekday {0:%A} and "
      "in two days it will be weekday "
      "{1:%A} timezone {0:%Z}".format(now, now + dtx.timedelta(days=2)))