Advanced python CoP

Table of contents:

• TDD
• Doctest
• Live coding

All you need to know about TDD in one picture:

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<img src=https://upload.wikimedia.org/wikipedia/commons/thumb/0/0b/TDD_Global_Lifecycle.png/2560px-TDD_Global_Lifecycle.png> 
</img>

Doctest - write simple unit tests in doc strings

def divide(a, b):
    """
    >>> divide(4,2)
    2.0
    >>> divide(2/0)
    Traceback (most recent call last):
      ...
    ZeroDivisionError: division by zero
    >>> a = 10
    >>> b = 5
    >>> divide(a,b)
    2.0
    """
    return a / b

Aaand that's all you need to know about writing doctests.

During development it's best to use IDE runner, but you can programatically run doctests from current file

import doctest
doctest.testmod(verbose=True)

Trying:
    divide(4,2)
Expecting:
    2.0
ok
Trying:
    divide(2/0)
Expecting:
    Traceback (most recent call last):
      ...
    ZeroDivisionError: division by zero
ok
1 items had no tests:
    __main__
1 items passed all tests:
   2 tests in __main__.divide
2 tests in 2 items.
2 passed and 0 failed.
Test passed.

TestResults(failed=0, attempted=2)

In automated tests you may use doctest discovery from pytest to find and run all doctests in module recursively

! pip install pytest --user

! pytest --doctest-modules

Live coding

import io
import re
from typing import Dict, Union

filename = "file.vbf"


def _remove_commented_lines(header_body: str) -> str:
    """
    >>> header = "before\\n // comment\\nafter"
    >>> _remove_commented_lines(header)
    'before\\n after'

    """
    return re.sub(r"//[^\n]+\n", "", header_body)


def _read_until(fp: io.BytesIO, pattern: str) -> None:
    """
    >>> file = io.BytesIO("trash header  {real_body".encode())
    >>> _read_until(file, r"header\s*{")
    >>> file.read().decode()
    'real_body'
    """
    value = ""
    while not re.search(pattern, value):
        value += fp.read(1).decode()


def extract_header_body(fp: io.BytesIO) -> str:
    """
    >>> extract_header_body(io.BytesIO("trash \\n header { body} other trash".encode()))
    "body"
    """
    _read_until(fp, r"header\s*{")
    # TODO: not finished
    return fp.read().decode()


def parse_vbf_header(header_body: str) -> Dict[str, Union[str, int]]:
    pass


with open(filename, "rb") as file:
    header_body = extract_header_body(file)
header = parse_vbf_header(header_body)