Python – Keycode

How to check the root cause of the difference between “pytest” and “python -m pytest”?

Command	Uses which Python?	Risk
`pytest`	Whatever executable is first in PATH	May run wrong environment
`python -m pytest`	The Python you explicitly called	Much safer

cat $(which pytest)

The shebang line can show which “python” that pytest uses.

python -c "import sys; print(sys.executable)"

which python

This shows the interpreter you’re explicitly invoking.

unittest setUp vs. pytest setup_class

unittest:

import unittest

class MyTest( unittest.TestCase ):
  def setUp( self ):
    self.variable = ...

pytest:

import pytest

class MyTest:
  @classmethod
  def setup_class( cls ):
    cls.variable = ...

Install pytorch cpu only

pip install torch --index-url https://download.pytorch.org/whl/cpu

Check where python packages are installed in a docker

Usually here:

/usr/local/lib/<python version>/site-packages

pip show request <package name>

Assert exception during python unit test

If using unittest:

import unittest

with self.assertRaises( Exception ) as error:
   ...

If using pytest:

import pytest

with pytest.raises( Exception ) as error:
   ...

Use ElementTree to add elements and sub-elements

import xml.etree.ElementTree as ET

root = ET.Element('Configuration')
student = ET.SubElement(root, 'student')
ET.SubElement(student, 'name').text = 'A'
ET.SubElement(student, 'years').text = '20'

# Test the result
import xml.dom.minidom
dom = xml.dom.minidom.parseString(ET.tostring(root))
print(dom.toprettyxml())

The result is below.

<?xml version="1.0" ?>
<Configuration>
	<student>
		<name>A</name>
		<years>20</years>
	</student>
</Configuration>

Pretty printing XML in Python


import xml.dom.minidom

dom = xml.dom.minidom.parse(xml_fname) 
# or 
# dom = xml.dom.minidom.parseString(xml_string)
pretty_xml_as_string = dom.toprettyxml()

Python unit test and nose test

unittest	nosetests
python -m unittest tests/test_something.py -v	nosetests tests/test_something.py -v
python setup.py test	python setup.py nosetests

Configure logging’s behavior once for all

An example Logging to multiple destinations in Logging Cookbook shows that we can configure logging‘s behavior once and then use the new behavior everywhere.

In one file LogAgent.py, we can configure logging‘s behavior as below.

// LogAgent.py

import logging

# set up logging to file - see previous section for more details
logging.basicConfig(level=logging.DEBUG,
                    format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s',
                    datefmt='%m-%d %H:%M',
                    filename='/temp/myapp.log',
                    filemode='w')
# define a Handler which writes INFO messages or higher to the sys.stderr
console = logging.StreamHandler()
console.setLevel(logging.INFO)
# set a format which is simpler for console use
formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
# tell the handler to use this format
console.setFormatter(formatter)
# add the handler to the root logger
logging.getLogger('').addHandler(console)

In another file A, we can use logging like below.

from LogAgent import *

logger1 = logging.getLogger('myapp.area1')

logger1.debug('Quick zephyrs blow, vexing daft Jim.')
logger1.info('How quickly daft jumping zebras vex.')

In another file B, we can use logging in the same way.

from LogAgent import *

logger2 = logging.getLogger('myapp.area2')

logger2.warning('Jail zesty vixen who grabbed pay from quack.')
logger2.error('The five boxing wizards jump quickly.')

Create a virtual environment

Create a virtual environment:

$ python3 -m venv myenv

Activate it:

$ source myenv/bin/activate
[myenv] $

Leave/Deactivate it:

[myenv] $ deactivate
$