Python Grymoire

Python Grymoire

Random tidbits that I need to reference every now and then. Everything is assumed python3

Exceptions

Template for custom exception stuff

class CustomError(Error):
    """Raised when there is a custom error"""
    pass

# The following all work
raise CustomError("Error message!")
raise CustomError()
raise CustomError

Printing full exception traceback

import traceback

try:
    1/0
except:
    traceback.print_exc()

Logging

import logging
logging.basicConfig(level=logging.DEBUG)
logger = logging.getLogger()

logger.debug()
logger.info()
logger.warning()
logger.error()
logger.critical()

For alternative methods of setting logger levels, look at the following. However, it appears that this is overwritten by logging.basicConfig

logger.setLevel(logging.DEBUG)
logger.getEffectiveLevel()

Regex

Don’t use re.match is anchored at the start of string. Use re.search

import re

match = re.search('meow', 'meow woof meow')
# only returns the first match
# match.group() to see thae matching object
# 'meow woof meow'[match.start(), match.end()] == 'meow'
# match is not None


match = re.search('meow', 'woof')
# match == None

match = re.findall('meow', 'meow woof meow')
# match == ['meow', 'meow']

Typing

from typing import Dict, List, Sequence, Tuple, Any
def example(
   first: str,
   second: str=None,
   third: Dict[str, str],
   fourth: Tuple[int, int],
   fifth: Any,
) -> str:

Unit Testing

Patching is difficult, and difficult to get right.

from unittest.mock import MagicMock, patch
patcher = patch(THE.REAL.STUFF, spec=True)
mock_the_real_stuff = patcher.start()
patcher.stop()


# or maybe
patcher.stopall()

patch vs patch.object

The former is a string path, and patch.object is an actual reference

type encoding

a = 'hello world'
b = a.encode # utf8 to binary
b.decode # binary to utf8

ord('v') == 118
chr(118) == 'v'