deyield.py

#!/usr/bin/env python3
""" Process .py file with nosetests assert_true etc for pytest

It does a fairly crude (regexp) job of taking lines nosetests lines like::

    yield assert_true, 1 == 2

and replacing them with::

    assert 1 == 2

suitable for pytest.

It will attempt to deal with multiline tests::

    yield assert_equal, 1 * 2 * 3, \
            2 * 3

should become::

    assert (1 * 2 * 3,
            2 * 3)

Use at your own risk!   Check the diff!
"""

from pathlib import Path

from argparse import ArgumentParser, RawDescriptionHelpFormatter

import re


YIELDER = re.compile(
    r'^(\s+)yield\s+(assert_[a-z_]+|pytest\.raises)\s*,\s*(.*)\s*\\?\s*$')


def proc_contents(contents):
    state = 'search'
    newline = '\n' if contents.endswith('\n') else ''
    sb = ''
    out_lines = []
    for line in contents.splitlines():
        line = line.rstrip()
        if state == 'search':
            if (match := YIELDER.match(line)):
                state = 'search'
                indent, asserter, args = match.groups()
                if asserter.startswith('('):
                    state = 'backslashed'
                    asserter = asserter[1:]
                elif line.endswith('\\'):
                    state = 'backslashed'
                sb = '(' if state in ('bracketed' or 'backslashed') else ''
                eb = '' if state == 'backslashed' else ')'
                if asserter == 'assert_true':
                    line = f'{indent}assert {sb}{args}'
                elif asserter == 'assert_false':
                    line = f'{indent}assert not {sb}{args}'
                elif asserter == 'assert_equal':
                    before, after = re.split(',\s*', args, 1)
                    line = f'{indent}assert {sb}{before} == {after}'
                elif asserter == 'pytest.raises':
                    line = f'{indent}pytest.raises({args}{eb}'
                else:
                    line = f'{indent}{asserter}({args}{eb}'
        elif state == 'backslashed':
            if not line.endswith('\\'):
                state = 'search'
                line += ')'
        elif state == 'bracketed':
            if line.endswith(')'):
                state = 'search'
        out_lines.append(line)
    return '\n'.join(out_lines) + newline


def process_py_file(py_file):
    py_file = Path(py_file)
    contents = py_file.read_text()
    fixed = proc_contents(contents)
    py_file.write_text(fixed)


def get_parser():
    parser = ArgumentParser(description=__doc__,  # Usage from docstring
                            formatter_class=RawDescriptionHelpFormatter)
    parser.add_argument('py_file',
                        help='Python filename')
    return parser


def main():
    parser = get_parser()
    args = parser.parse_args()
    process_py_file(args.py_file)


if __name__ == '__main__':
    main()