Programming languages

The simplest way of getting the current time as np.datetime64 object is to combine datetime.datetime.now() and the np.datetime64() constructor:

from datetime import datetime
import numpy as np

dt_now = np.datetime64(datetime.now())

print(dt_now)

Or use this function for convenience:

from datetime import datetime
import numpy as np

def datetime64_now():
    return np.datetime64(datetime.now())

dt_now = datetime64_now()
print(dt_now)

datetime64_now() is also available on my library UliEngineering.
Install using sudo pip3 install -U UliEngineering, then use like this:

from UliEngineering.Utils.NumPy import datetime64_now

dt_now = datetime64_now()
print(dt_now)

Usually you can list all attributes and functions of a Python object using __dir__:

from collections import namedtuple
nt = namedtuple("Foo", [])
print(nt.__dict__) # Prints attributes and functions of nt.

This can be very useful to find out e.g. which functions you can call on an object:

However for some objects like datetime.datetime this doesn’t work. Attempting to run

from datetime import datetime
dt = datetime.now()
print(dt.__dict__)

will result in

Traceback (most recent call last):
  File "test.py", line 3, in <module>
AttributeError: 'datetime.datetime' object has no attribute '__dict__'

So how can you find out which attributes your datetime.datetime object has and what function you can call on it?

Use dir():

from datetime import datetime
dt = datetime.now()
print(dir(dt))

This will print e.g.

['__add__', '__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__ne__', '__new__', '__radd__', '__reduce__', '__reduce_ex__', '__repr__', '__rsub__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', 'astimezone', 'combine', 'ctime', 'date', 'day', 'dst', 'fold', 'fromordinal', 'fromtimestamp', 'hour', 'isocalendar', 'isoformat', 'isoweekday', 'max', 'microsecond', 'min', 'minute', 'month', 'now', 'replace', 'resolution', 'second', 'strftime', 'strptime', 'time', 'timestamp', 'timetuple', 'timetz', 'today', 'toordinal', 'tzinfo', 'tzname', 'utcfromtimestamp', 'utcnow', 'utcoffset', 'utctimetuple', 'weekday', 'year']

Minimal example with one positional parameter (param):

#!/usr/bin/env python3
import argparse

if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("param")
    args = parser.parse_args()
    # Your code goes here!
    print(args.param)

Minimal example with one argument (-p, --param):

#!/usr/bin/env python3
import argparse

if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("-p", "--param")
    args = parser.parse_args()
    # Your code goes here!
    print(args.param)

Here’s a minimal example for a custom class that is iterable similar to a generator:

class MyIterable(object):
    def __init__(self):
        pass # ... Your code goes here!

    def __iter__(self):
        # Usually there is no need to modify this!
        return self

    def __next__(self):
        # To indicate no further values, use: raise StopIteration
        return "test" # Return the next value here. Return n

Usage example:

it = MyIterable()
print(next(it)) # Prints "test"
print(next(it)) # Prints "test"

In case you want to read more about how to create your own iterators, I recommend this tutorial.

In this example, we’ll use the UliEngineering library to convert between the three most commonly used units of temperature: Celsius (°C), Fahrenheit (°F) and Kelvin (K)

In order to install UliEngineering (a Python 3 library) run:

sudo pip3 install -U UliEngineering

We can now use the following functions from the UliEngineering.Physics.Temperature package to convert between the units of temperature:

• celsius_to_kelvin(temperature)
• kelvin_to_celsius(temperature)
• fahrenheit_to_kelvin(temperature)
• fahrenheit_to_celsius(temperature)

Tip: You can pass both numbers (like 120) or strings (like 120 °C or 0.01 °F) to most UliEngineering functions. SI prefixes like k and m are automatically decoded.

Example:

from UliEngineering.EngineerIO import auto_print
from UliEngineering.Physics.Temperature import *

# Convert to celsius and store in variable
temp = fahrenheit_to_celsius("120 °F") # temp = 48.88888888888897

# Automatically format value & print. Prints "48.9 °C"
auto_print(fahrenheit_to_celsius, "120 °F")

Additionally, UliEngineering provides normalize_temperature_celsius(temp, default_unit="°C") which takes a string and automatically recognizes the unit (if there is no unit given, the default_unit is assumed).

Examples:

• normalize_temperature_celsius("120 °C") == 120.0
• normalize_temperature_celsius("120") == 120.0
• normalize_temperature_celsius(120) == 120.0
• normalize_temperature_celsius("120 °F") == 48.88888888888897
• normalize_temperature_celsius("120 K") == -153.14999999999998
• auto_print(normalize_temperature_celsius, "120 K") prints -153.15 °C

Note that while °K is recognized by UliEngineering‘s functions, K is correctly used without a degree symbol.

Also there is normalize_temperature(temp, default_unit="°C") which is equivalent to normalize_temperature_celsius() except it returns the temperature in Kelvin instead of degrees Celsius.

Problem:

You want to test a Python package e.g. using python setup.py test.  However, you see the following error message:

usage: setup.py [global_opts] cmd1 [cmd1_opts] [cmd2 [cmd2_opts] ...]
   or: setup.py --help [cmd1 cmd2 ...]
   or: setup.py --help-commands
   or: setup.py cmd --help

error: option --rednose not recognized

Solution:

Rednose is a Python package that you need to install:

sudo pip3 install rednose

or, if you don’t have pip3, try

sudo pip install rednose