# Buggy code
def read(self, filenames):
    from coverage.optional import toml

    # RawConfigParser takes a filename or list of filenames, but we only
    # ever call this with a single filename.
    assert isinstance(filenames, path_types)
    filename = filenames
    if env.PYVERSION >= (3, 6):
        filename = os.fspath(filename)

    try:
        with io.open(filename, encoding="utf-8") as fp:
            toml_text = fp.read()
    except IOError:
        return []
    if toml:
        toml_text = substitute_variables(toml_text, os.environ)
        try:
            self.data = toml.loads(toml_text)
        except toml.TomlDecodeError as err:
            raise TomlDecodeError(*err.args)
        return [filename]
    else:
        has_toml = re.search(r"^\[tool\.coverage\.", toml_text, flags=re.MULTILINE)
        if self.our_file or has_toml:
            # Looks like they meant to read TOML, but we can't read it.
            msg = "Can't read {!r} without TOML support. Install with [toml] extra"
            raise CoverageException(msg.format(filename))
        return []


# Traceback (KeyError)
Traceback (most recent call last):
...
File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/coverage/control.py", line 195, in __init__
self.config = read_coverage_config(
File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/coverage/config.py", line 530, in read_coverage_config
config_read = config.from_file(fname, our_file=our_file)
File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/coverage/config.py", line 275, in from_file
files_read = cp.read(filename)
File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/coverage/tomlconfig.py", line 32, in read
from coverage.optional import toml
File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/coverage/optional.py", line 51, in <module>
import toml
File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/toml/__init__.py", line 6, in <module>
from toml import encoder
File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/toml/encoder.py", line 4, in <module>
from decimal import Decimal
File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/decimal.py", line 3, in <module>
from _decimal import *
KeyError: 'numbers'

# Fixed code
def read(self, filenames):
    # RawConfigParser takes a filename or list of filenames, but we only
    # ever call this with a single filename.
    assert isinstance(filenames, path_types)
    filename = filenames
    if env.PYVERSION >= (3, 6):
        filename = os.fspath(filename)

    try:
        with io.open(filename, encoding="utf-8") as fp:
            toml_text = fp.read()
    except IOError:
        return []
    if toml:
        toml_text = substitute_variables(toml_text, os.environ)
        try:
            self.data = toml.loads(toml_text)
        except toml.TomlDecodeError as err:
            raise TomlDecodeError(*err.args)
        return [filename]
    else:
        has_toml = re.search(r"^\[tool\.coverage\.", toml_text, flags=re.MULTILINE)
        if self.our_file or has_toml:
            # Looks like they meant to read TOML, but we can't read it.
            msg = "Can't read {!r} without TOML support. Install with [toml] extra"
            raise CoverageException(msg.format(filename))
        return []