Tips and Tricks

Get nested attribute with dot notation

Interesting application for the reduce function is to access attribute of nested objects:

import functools

def get_attr(obj, attr):
    return functools.reduce(getattr, attr.split('.'), obj)

import dataclasses

@dataclasses.dataclass
class Address:
    city: str

@dataclasses.dataclass
class User:
    name: str
    address: Address

Now if we want to access the city of the user, we acually need to access the address of the user and than the city of the address. Expressed in dot notation we want to access address.city :

>>> address = Address('Sofia')
>>> user = User('john', address)
>>> print(get_attr(user, 'address.city'))
Sofia

Trying to access missing attribute results in AttributeError error:

>>> address = Address('Sofia')
>>> user = User('john', address)
>>> print(get_attr(user, 'floor'))
Traceback (most recent call last):
...
AttributeError: 'Address' object has no attribute 'floor'

This function has been included in pygems.core.shortcuts module.

Capture function execution time

The pygems.core.timer.Timer class implements the decorator protocol. You can capture the execution time of a function using the pygems.core.timer.Timer class as decorator.

from pygems.core.timer import Timer

@Timer(stop_func=lambda t: print(f'{t.elapsed}s'))
def slow_function():
    # do your work here
    pass

Each time the slow_functoin() is called, the elapsed time for the function execution is printed to the console.

>> slow_function()
3.1e-06s

The pygems.core.timer.Timer calls the passed stop_func function when the function has finished its execution.

In the above example we pass a lambda function which simply prints the elapsed seconds.

You could make the timer to log a message:

import logging
from pygems.core.timer import Timer

logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

def stop_func(t:Timer, *args):
    logger.info(f'{t.name}: elapsed {t.elapsed}s')


@Timer(name='slow_function', stop_func=stop_func)
def slow_function():
    # do your work here
    pass

Now when the slow_function is called a message is added to the log which includes the name of the timer and the elapsed time.

>> slow_function()
INFO:__main__:slow_function: elapsed 6.499999983589078e-06s

Capture the execution time of Python block

pygems.core.timer.Timer implements the context manager protocol. This can be used to capture the time required to execute a block of code in Python.

You can pass any function as stop_func argument to the Timer class. The function will be called at the end of the block with the timer instance as first argument.

>>> from pygems.core.timer import Timer
>>> with Timer(name='slow-block', stop_func=lambda t: print(f'{t.name}: {t.elapsed}s')):
>>>     # run your code here
>>>     pass
slow-block: 3.999999989900971e-06s

Similarly the execution time of the block could be logged using Python’s logging module:

>>> import logging
>>> from pygems.core.timer import Timer
>>> logging.basicConfig(level=logging.INFO)
>>> with Timer(name='slow-block', stop_func=lambda t: logging.info(f'{t.name}: {t.elapsed}s')):
>>>     # run your code here
>>>     pass
INFO:root:slow-block: 1.5699999948992627e-05s