Category: Python

Sometimes, we want to change backends in matplotlib and Python.

In this article, we’ll look at how to change backends in matplotlib and Python.

How to change backends in matplotlib and Python?

To change backends in matplotlib and Python, we call use and then reload.

For instance, we write

import matplotlib

matplotlib.use('agg')

matplotlib = reload(matplotlib)
matplotlib.use('cairo.png')

to call matplotlib.use to set the back end.

And then we call reload with matplotlib and set the returned object back to matplotlib to reload the object.

And then we call use again to change the backend.

Conclusion

To change backends in matplotlib and Python, we call use and then reload.

Sometimes, we want to plot multiple bars with Python matplotlib.

In this article, we’ll look at how to plot multiple bars with Python matplotlib.

How to plot multiple bars with Python matplotlib?

To plot multiple bars with Python matplotlib, we can call bar to multiple times.

For instance, we write

import matplotlib.pyplot as plt
from matplotlib.dates import date2num
import datetime

x = [
    datetime.datetime(2021, 1, 4, 0, 0),
    datetime.datetime(2021, 1, 5, 0, 0),
    datetime.datetime(2021, 1, 6, 0, 0)
]
x = date2num(x)

y = [4, 9, 2]
z = [1, 2, 3]
k = [11, 12, 13]

ax = plt.subplot(111)
ax.bar(x-0.2, y, width=0.2, color='b', align='center')
ax.bar(x, z, width=0.2, color='g', align='center')
ax.bar(x+0.2, k, width=0.2, color='r', align='center')
ax.xaxis_date()

plt.show()

to create the x list with some dates.

Then we call date2num with x to convert the dates to values that can be plotted.

Next, we create a subplot with subplot.

And we call ax.bar to plot the bars with diffent x and y values.

We also set the color of the bars to different colors and change the alignment of them by setting align.

And we call xaxis_date to render the x-axis labels as dates.,

Conclusion

To plot multiple bars with Python matplotlib, we can call bar to multiple times.

Sometimes, we want to access a dictionary element in a Django template with Python.

In this article, we’ll look at how to access a dictionary element in a Django template with Python.

How to access a dictionary element in a Django template with Python?

To access a dictionary element in a Django template with Python, we can use the items property to get the key-value pairs.

For instance, if we have

choices = {'key1':'val1', 'key2':'val2'}

Then we can render the key-value pairs in the template with

<ul>
{% for key, value in choices.items %} 
  <li>{{key}} - {{value}}</li>
{% endfor %}
</ul>

We get the key-value pairs with choices.items.

And then we render the values with the for loop.

Conclusion

To access a dictionary element in a Django template with Python, we can use the items property to get the key-value pairs.

Sometimes, we want to run Django filter queryset __in for every item in list with Python.

In this article, we’ll look at how to run Django filter queryset __in for every item in list with Python.

How to run Django filter queryset __in for every item in list with Python?

To run Django filter queryset __in for every item in list with Python, we can use the itertools.reduce method.

For instance, we write

from operator import and_
from django.db.models import Q

categories = ["holiday", "summer"]
res = Photo.filter(reduce(and_, [Q(tags__name=c) for c in categories]))

to call reduce with the and_ operator and the list of querysets [Q(tags__name=c) for c in categories] to combine them with logical AND.

Then we call filter with the combined query set returned by reduce.

Conclusion

To run Django filter queryset __in for every item in list with Python, we can use the itertools.reduce method.

Sometimes, we want to fix Python app does not print anything when running detached in Docker.

In this article, we’ll look at how to fix Python app does not print anything when running detached in Docker.

How to fix Python app does not print anything when running detached in Docker?

To fix Python app does not print anything when running detached in Docker, we run python with the -u flag in our Dockerfile.

For instance, we write

CMD ["python","-u","main.py"]

to run main.py with -u to use unbuffered output.

conclusion

To fix Python app does not print anything when running detached in Docker, we run python with the -u flag in our Dockerfile.